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Auto Focus Accuracy and Precision for the D800/D800e

GiantTristan

Stamford, US
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GiantTristan Silver Member Nikonian since 08th Jan 2006
Wed 15-Aug-12 04:03 PM

Some of you might be interested in Lloyd Chambers' take on the above subject matter: 08/11/12 blog, http://www.digilloyd.com
I believe that Mr. Chambers is one of the more competent Internet Gurus, and his thoughts are definitely worth considering.

Just a personal disclaimer - I don't own a D800/800e and probably never will.

Tristan

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Skyco

Roanoke Island, US
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#1. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 0

Skyco Silver Member Nikonian since 12th Mar 2012
Wed 15-Aug-12 09:16 PM

>Some of you might be interested in Lloyd Chambers' take on
>the above subject matter: 08/11/12 blog,
>http://www.digilloyd.com
>I believe that Mr. Chambers is one of the more competent
>Internet Gurus, and his thoughts are definitely worth
>considering.
>
>Just a personal disclaimer - I don't own a D800/800e and
>probably never will.

I read what Lloyd Chambers had to say about the D800/D800e and other Nikons as well- he does include other Nikon cameras.

What he says does not fit with my D800 - or for that matter other Nikons I have used. He said Nikon has unreliable auto focus. My experience with my D800 has been excellent. If you never get a D800 you will be missing out on way more than just 36 mp. Its an awesome and fantastic camera!

Mr. Chambers comments on the D800 and Nikon cameras (he talks about his wife's Nikon remember) just do not ring true for me. I can not take him seriously.

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infamily

Petaluma, US
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#2. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 1

infamily Silver Member Donor Ribbon awarded for his support to the Fundraising Campaign 2014 Nikonian since 10th Sep 2009
Thu 16-Aug-12 12:31 AM

I agree. My d800 is simply awesome and focus is right on.

Why take the trouble to read and post if you are not planning to buy these cameras?

Sandeep B
So much to learn, so little time.

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my Nikonians gallery.

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ShaoLynx

Tienen, BE
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#3. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 0

ShaoLynx Gold Member Nikonian since 17th Aug 2010
Thu 16-Aug-12 04:03 AM

Indeed,
I understand that in your country, the US that is, freedom of speech also means that you can lie and insinuate your ass off. That's were that freedom goes too far. Abuse of freedom (for the wrong reasons, obviously) is just wrong.
Where I live, there is freedom of speech, too. And we also have social media, in which you get crucified for blogs or websites like Lloyds'. In the US you have that, too.

For the record: I myself have both the D700 and the D800, and let me tell you: the D800 is so much better. No, no focus problem, neither left, right or in the middle, and yes, I do use all of the focus points in order to get the right compo with focus spot on. And no, the pop-up flash does not rattle if I hold my camera (nor when I shake it), and there is no light leak either, so I don't need duct tape,... Oh wait, that's for...

I do apologize to the honorable people here on Nikonians if my rant was a bit harsh, but that website and this OP really struck a nerve to my sense of righteousness.

Garrett Hayes

Lucan, Ireland, IE
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#4. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 1

Garrett Hayes Gold Member Nikonian since 03rd Nov 2004
Thu 16-Aug-12 04:20 AM

I agree with the comments here. In my experience, the focusing has been excellent and I have posted a number of pictures on the D800 facebook page which give the lie to these comments.

Bias comes from all quarters for various reasons

GH

AreBee

Inverness, UK
531 posts

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#5. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 0

AreBee Registered since 27th Apr 2008
Thu 16-Aug-12 10:51 AM

To those claiming perfect focus from the camera's Phase Detect autofocus system, if this were true 100% of the time then there would be no requirement for the Contrast Detect autofocus sysem which is slower but consistently more accurate.

Rob
www.robbuckle.co.uk

ericbowles

Atlanta, US
10631 posts

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#6. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 0

ericbowles Moderator Awarded for his in-depth knowledge and high level skills in various areas, especially Landscape and Wildlife Photoghraphy Writer Ribbon awarded for for his article contributions to the community Donor Ribbon awarded for his very generous support to the Fundraising Campaign 2015 Nikonian since 25th Nov 2005
Thu 16-Aug-12 11:18 AM | edited Thu 16-Aug-12 11:23 AM by ericbowles

Thanks for sharing the link to Lloyd's comments.

Lloyd is one of the most critical people around - and a real techie who compares things to highest end glass and medium format bodies. For perspective, I think he would find fault with any piece of gear made by Nikon (or Canon) over the past 10 years. His standard is well beyond that of full time commercial photographers. Lloyd does make a good distinction between precision of focus and accuracy of focus.

My understanding is the way he uses the term Precision would technically be referred to as the standard deviation of the focus errors. In other words, if 75% of the AF attempts are perfect, but it misses badly a few times in both directions, that is a problem.

AF accuracy would be the mean AF error - and if on average you are getting errors, you would fine tune for the lens to move the average closer to perfect AF.

The blog at LensRentals.com covered this in a discussion of lenses AF not the camera body. Some lenses have wider variation or a greater standard deviation than others. And no lens is perfect - there is variation in all AF systems just as there is variation in Manual Focus.

I'm not sure why you would test an 85mm lens at a distance of 80 feet. It's a wonderful portrait lens and great for distances of 20 feet and less. That's like testing a macro lens for the landscape. Again, lensrentals.com had a very recent blog post that reported test results for the Nikon 105 at a distance of 15 feet vs. macro distance. The lens tested much better at macro distance. And they attributed focus quality to be a lens attribute.

I do think it is worth taking a look at AF precision. What LensRentals found is there is variation in all lenses, but in general AF was pretty close unless these was a mechanical problem - which was uncommon. They took hundreds of shots and displayed summary data in the blog. The testing using FoCal does something similar.

The conclusion of LensRentals - and I agree - is that focus errors are normal whether you focus manually or using AF. The AF systems of today are a lot better than earlier systems - and better than manual focus for many situations. And we need to understand that there are tolerances for AF that involve both the lens and the camera.

I have found that the ability to pixel peep on the D800 means we are much more aware of focus errors that would not show up at all in a file resized to a D700 or D3 size.

Eric Bowles
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Skyco

Roanoke Island, US
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#7. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 3

Skyco Silver Member Nikonian since 12th Mar 2012
Thu 16-Aug-12 11:25 AM

Hello Geert,

>I do apologize to the honorable people here on Nikonians if my
>rant was a bit harsh, but that website and this OP really
>struck a nerve to my sense of righteousness.

Your good. You don't need to apologize in my opinion. I agree with your every word!

The people who I think should apologize to the honorable people here on Nikonians are the ones who have no interest in owning a D800 - but post complaints about the camera and repeat lies and nonsense of the Brand X trolls and clowns.

I was so angry after reading the OP and link that it took me a while to calm down before replying. Even then I deleted a lot of what I had written.

Well Wishes,

Ken

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RECONLEY

Marietta, US
585 posts

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#8. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 5

RECONLEY Silver Member Nikonian since 18th Jun 2012
Thu 16-Aug-12 12:46 PM

>To those claiming perfect focus from the camera's Phase
>Detect autofocus system, if this were true 100% of the time
>then there would be no requirement for the Contrast Detect
>autofocus sysem which is slower but consistently more
>accurate
.
For a start there is not now nor has there ever been a camera with "Perfect" auto focus. What we have had is good enough that continues to get better with each new generation of camera body. This is true with all camera manufacturers.

Also, there is a need (at least a perceived need) by many that use the LV for composition, as well as, AF.

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jerry r

US
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#9. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 6

jerry r Registered since 08th Oct 2008
Thu 16-Aug-12 01:10 PM

Eric,

Well written.

I always respect your posts. They are informative, helpful and to the point.

Jerry

rplst8

Johnstown, US
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#10. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 5

rplst8 Silver Member Nikonian since 18th Dec 2008
Thu 16-Aug-12 01:16 PM

We don't have CDAF because it's more accurate. In fact, there are many situations where CDAF might be less accurate.

The reason we have CDAF is because since the mirror is locked up during live view or video shooting, the PDAF system is inoperable.

CDAF may, on average, be more accurate but that's not why we have it.

--
RL

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rplst8

Johnstown, US
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#11. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 6

rplst8 Silver Member Nikonian since 18th Dec 2008
Thu 16-Aug-12 01:39 PM | edited Thu 16-Aug-12 01:42 PM by rplst8

>My understanding is the way he uses the term Precision would
>technically be referred to as the standard deviation of the
>focus errors. In other words, if 75% of the AF attempts are
>perfect, but it misses badly a few times in both directions,
>that is a problem.
>
>AF accuracy would be the mean AF error - and if on average you
>are getting errors, you would fine tune for the lens to move
>the average closer to perfect AF.


I don't think this correctly describes accuracy or precision for any application.

If I initiate autofocus 100 times, and 99 times it is out of focus, but by the exact same amount, the AF system is precise but not accurate. This is the prefered situation, as a simple offset value (AF fine tune) will center the result on the proper point.

If I initiate autofocus 100 times and 99 times it is out of focus, but it is out of focus by small amount in either direction of the correct focus point by an equal emount, this is said to be accurate (but not precise). This is more difficult to fix because a simple offset will not help.

In my experience the D800 is very very precise (as are other cameras made by Nikon) at a given focus point. However, its accuracy varies per selected focus point. Some focus points are dead nuts on, others are not.

If the variation between all the focus points is averaged, it may turn out that the camera (on average) is neither accurate nor precise. This would negatively affect focus tracking modes.

>The blog at LensRentals.com covered this in a discussion of
>lenses AF not the camera body. Some lenses have wider
>variation or a greater standard deviation than others. And no
>lens is perfect - there is variation in all AF systems just as
>there is variation in Manual Focus.
>
>I'm not sure why you would test an 85mm lens at a distance of
>80 feet. It's a wonderful portrait lens and great for
>distances of 20 feet and less.


For normal (not macro) lenses, this shouldn't matter. The DoF increases with distance. Therefore, it should be easy to design optics that are accurate at close range (shallow DoF) and remain accurate at distance (due to more allowable slop).

Macro lenses are much different IMO as there is extention involved and other optical tricks.

>I do think it is worth taking a look at AF precision. What
>LensRentals found is there is variation in all lenses, but in
>general AF was pretty close unless these was a mechanical
>problem - which was uncommon. They took hundreds of shots and
>displayed summary data in the blog. The testing using FoCal
>does something similar.
>
>The conclusion of LensRentals - and I agree - is that focus
>errors are normal whether you focus manually or using AF. The
>AF systems of today are a lot better than earlier systems -
>and better than manual focus for many situations. And we need
>to understand that there are tolerances for AF that involve
>both the lens and the camera.


I agree that there is variation and allowable tolerance - but it shouldn't change (by much) depending on which AF point you use, other than which subjects are acceptable (i.e. outer focus points only detect vertical detail while center points are cross type).

>I have found that the ability to pixel peep on the D800 means
>we are much more aware of focus errors that would not show up
>at all in a file resized to a D700 or D3 size.


This is where I disagree. Maybe compared to the D700 or D3 resolution but not with the D300. The D800 is in a lot of ways similar to the D300 and D300s. They both have 51 point AF sensors. Both of their AF sensor arrays cover only the DX frame. They also only differ by about 15% in resolution over the DX frame (2800 lines for the D300 and 3200 lines for the D800).

Yet the D300 had NO percieved or real auto focus problems. PDAF was accurate, fast, and worked very well (even for photos cropped at 100%). The number of lines of resolution under a given AF sensor are nearly the same for the D300 and D800. A 15% change in resolution is not enough to make a picture go from "in focus" to "out of focus".

As I've demonstrated in another thread, even at 1/4 the resolution (equivalent of 2.3 MP) missed focus shots with the left AF sensor still appear out of focus. This is NOT a pixel peeping problem. This is a QC and calibration problem.

--
RL

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ericbowles

Atlanta, US
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#12. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 11

ericbowles Moderator Awarded for his in-depth knowledge and high level skills in various areas, especially Landscape and Wildlife Photoghraphy Writer Ribbon awarded for for his article contributions to the community Donor Ribbon awarded for his very generous support to the Fundraising Campaign 2015 Nikonian since 25th Nov 2005
Thu 16-Aug-12 04:08 PM

<I don't think this correctly describes accuracy or precision for any application.

<If I initiate autofocus 100 times, and 99 times it is out of focus, but by the exact same amount, the AF system is precise but not accurate. This is the prefered situation, as a simple offset value (AF fine tune) will center the result on the proper point.

<If I initiate autofocus 100 times and 99 times it is out of focus, but it is out of focus by small amount in either direction of the correct focus point by an equal emount, this is said to be accurate (but not precise). This is more difficult to fix because a simple offset will not help.>

The author, Lloyd Chambers - linked to a Wikipedia article for his definition of precision and accuracy. Variation / standard deviation is a measure of precision while accuracy is measured by looking at the average. The author specifically refers to accuracy errors being corrected through fine tuning, but the lack of precision or variation - as measured by standard deviation - cannot be addressed. It is essentially random error that is outside of his acceptable tolerances.

He's not talking about the left sensor issues at all and my comments are not about the left sensor. We've covered that issue in other threads. For those that have the issue - and I do - it is significant with that one sensor but other sensors that I use much more often are just fine.

Here's a link to one of the LensRentals.com articles. They have graphed the focus precision (Lloyd's term) and used standard deviation across Canon DSLR bodies. The Nikon DSLR bodies are probably similar.
http://www.lensrentals.com/blog/2012/08/autofocus-reality-part-3b-canon-cameras

The focus variation issue has been there for every Canon DSLR - and is generally improving. I have no reason to think Nikon is different but have not seen any data either way. I would love to see LensRentals test the Nikon DSLR lineup the way they tested Canon as it would confirm or contradict Lloyd's experience.

I would expect every AF sensor would have some possibility of variation. Certainly the cross sensors and center sensor are different. Add to that, the variation created by the electronic mechanism that focuses the lens, and you have many ways for AF to miss focus.

As far as focus quality variation is concerned, we've seen differences based on focal length of zoom lenses, target distance, exposure value, ISO, and even white balance. All those are without consideration of the camera or the lens.



Eric Bowles
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AreBee

Inverness, UK
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#13. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 8

AreBee Registered since 27th Apr 2008
Thu 16-Aug-12 05:16 PM

Roy,

>For a start there is not now nor has there ever been a camera with "Perfect" auto focus.<

I never claimed there was.

>What we have had is good enough that continues to get better with each new generation of camera body. This is true with all camera manufacturers.<

Good enough for whom, exactly? How would you know what I or others consider to be "good enough"? What makes you think I or others settle for "good enough"?

We each have different standards, so "good enough" cannot possibly be acceptable to everyone.

>Also, there is a need (at least a perceived need) by many that use the LV for composition, as well as, AF.<

Not sure what you are tying to convey here.

Rob
www.robbuckle.co.uk

AreBee

Inverness, UK
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#14. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 10

AreBee Registered since 27th Apr 2008
Thu 16-Aug-12 05:24 PM

Ryan,

>The reason we have CDAF is because since the mirror is locked up during live view or video shooting, the PDAF system is inoperable.<

Thank you for the correction.

Rob
www.robbuckle.co.uk

rplst8

Johnstown, US
150 posts

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#15. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 12

rplst8 Silver Member Nikonian since 18th Dec 2008
Thu 16-Aug-12 05:37 PM

I don't take issue with Wikipedia or the Lensrentals.com blog descriptions.

I take issue with your description:

>In other words, if 75% of the AF attempts are perfect, but it misses badly a few times in both directions, that is a problem.

I don't think this is a good example of precise/accurate or imprecise/inaccurate behavior.

--
RL

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GiantTristan

Stamford, US
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#16. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 15

GiantTristan Silver Member Nikonian since 08th Jan 2006
Thu 16-Aug-12 07:35 PM | edited Thu 16-Aug-12 09:35 PM by GiantTristan

>>In other words, if 75% of the AF attempts are perfect,
>but it misses badly a few times in both directions, that is a
>problem.

>
>I don't think this is a good example of precise/accurate or
>imprecise/inaccurate behavior.

Maybe one should look at the data this way: 75% of the shots are "in focus" or within the control limits for the AF. Assuming normal error distribution, the AF is in spec about one standard deviation (66%). This obviously is totally unacceptable. The precision should be at least two SD or 95% , probably more like three SD or about 99% in spec. Since the AF misses in both directions, the accuracy is apparently ok.

Tristan

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TomCurious

Bay Area, US
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#17. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 0

TomCurious Registered since 03rd Jan 2007
Fri 17-Aug-12 01:45 AM

A few comments:

1. From knowing Lloyd personally and having been on a shoot with him testing some lenses, I am sure he would not lie to drive traffic to his site or for any other reason.

2. He works painstakingly detail-oriented and looks for the smallest issues and reports them. While being on a shoot with him, there were times when he saw a focus issue, and I did not, and only after he pointed it out to me while looking at the LCD at 100% and with a loupe attached, I could see it. I would never have found such issues if I were on my own. That's not to say that some issues he reports on may not be big and obvious, but he reports every issue, however small. This can be very useful, you just need to know about it (and read the details on his paid section).

3. The blog that was referred to in the OP notes that the focus precision issues are for a very specific scenario: Shooting a target about 80ft away and with a lens set to f/1.4. I've never had such scenario in my life, ever. At f/1.4 I shoot portraits only.

I hope this will put this issue to rest.

Tom
Bay Area Nikonian


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Clint S

Chula Vista, US
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#18. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 0

Clint S Silver Member Nikonian since 02nd Jan 2011
Fri 17-Aug-12 05:18 AM

I do not see much worth in Lloyd Chambers' comments. How do they relate to real life? Real life being the final product.


All things have variances in precision and accuracy. The higher the
level of precision the more costly the product. The higher the level of accuracy, the more costly the product. Because there is no perfect, there must be case of "good enough" for the associated cost.


Good enough in the clarity of a photograph is often described in the depth of field, which is ultimately based on the final product.
Since Depth of field is computed based on the Circle of Confusion, which is based on the final product - until you define the latter there is no logical discussion that can be meaningful. I did not see that in Lloyd Chambers' writings.


And then terminology needs to be clearly understood, average does not necessarily equal the means and vice vera. A standard deviation or Sigma is often misunderstood. When dealing with variances, understanding what standard deviation is, and when it is proper to use (and maybe even more important when not to use) standard deviations are significantly important. A standard deviation is not a means of measurement but a representative number of the variance(s) involved. And without enough samplings, a determined standard deviation is worthless.


It is all too easy to say things should be more accurate or have more precision, but till those are defined in real world outcomes and results, stating levels of precision and accuracy without knowledge in the affects is detrimental. Accuracy and precision can both be improved, but it comes at a cost!


Lloyd Chambers comments may represent his data truthfully, but his data by itself is not significant enough to base any theories or determinations on.

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pic

US
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#19. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 5

pic Silver Member Charter Member
Fri 17-Aug-12 07:45 AM

In testing my lenses for focus in both modes, I discovered that on certain older screw-focus models, the CDAF consistently overdrove the lens past the desired focus point. In such cases, the PDAF was consistently better and virtually indistinguishable from live view manual focus.

This is why it is so important to test your equipment and know its behavior under various conditions.

ericbowles

Atlanta, US
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#20. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 16

ericbowles Moderator Awarded for his in-depth knowledge and high level skills in various areas, especially Landscape and Wildlife Photoghraphy Writer Ribbon awarded for for his article contributions to the community Donor Ribbon awarded for his very generous support to the Fundraising Campaign 2015 Nikonian since 25th Nov 2005
Fri 17-Aug-12 09:16 AM

Tristan has the right idea. The amount of the standard deviation is as important as a more arbitrary measure of how many standard deviations are used to measure acceptable performance. We don't have any data on the size and frequency of focus errors. Lensrentals.com found a significant reduction in the standard deviation for Canon -meaning the amount of variation was reduced with each new generation. In contrast, Lloyd believes that the standard deviation is abnormally large on the D800. Even though he can correct for accuracy with fine tuning, he can't do anything about random missed focus. And if the miss is large it means a discarded image.

I have not seen the wide variation with the center sensor that Lloyd describes, but I also have not done rigorous testing.

Eric Bowles
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lukaswerth

Lahore, PK
576 posts

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#21. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 18

lukaswerth Registered since 24th May 2012
Fri 17-Aug-12 09:37 AM

I have not subscribed to Chambers' website, but I read a bit of his free stuff and his blog. His website seems to be on a much higher level than, for instance, Rockwell's stuff - much of it seems to be, however, for technical freaks. I have the lenses I want to use in the coming time, why should I learn about the performance of every lens there is?
With regard to focus issues: I like to try my gear myself and see whether it performs well for me, for my needs. It is my experience that every gear has weaknesses, there is never such a thing as perfectness. A photographer must know what can and what cannot be done with her/his gear, and ways to work around some issues (focusing manually when the situation demands it??). This is part of her/his craft.

Lukas

Trying to be a keeper of the light

Ferguson

Cape Coral, US
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#22. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 0

Ferguson Silver Member Fellow Ribbon awarded for the generous sharing of his high level expertise in the spirit of Nikonians Nikonian since 19th Aug 2004
Fri 17-Aug-12 11:46 AM

I have a D800 and like it, but a lot of Lloyd's comments ring true. One aspect of the D800 is more "chatter" from the AF system than my D300 ever had, I commented on it here in another thread. It rarely seems to quite settle in, even in good light and normal subjects if you watch and listen, you hear it continually making tiny adjustments.

"But that's normal" is what most answer, and that's a true statement also, but a question of degree -- the D800 chatters more than any other camera I have had (including the D4). It seems like their algorithm and/or control is not adequately damped; on perfectly stationary objects and camera it still thinks it needs to change, then change again. These small changes may also come from imprecision -- it is taking multiple measurements, and if they are not the same, it assumes a need to adjust focus again.

I'm sure that is over-simplified, but as I said -- the comments ring true.

Is it imprecise enough to matter? I'm happy with its precision. I get enough keepers to be satisfied, except with my 85/1.4 where the jury is still out. But Lloyd's handling of "precision" and "accuracy" were right on. They are well defined engineering terms and not matters of opinion, and nice to see them used properly. Is Canon significantly different? Who knows.

But to all the people who show an in-focus shot and say "see, he's wrong" -- just remember, a stopped clock is perfectly accurate twice a day, and is perfectly precise all the time.

It's not just about the results of testing, it's about the images you capture, and there I am happy with the D800. It's off getting the left focus fixed, but that's a very different issue.


Linwood

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rplst8

Johnstown, US
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#23. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 22

rplst8 Silver Member Nikonian since 18th Dec 2008
Fri 17-Aug-12 02:04 PM

>I have a D800 and like it, but a lot of Lloyd's comments ring
>true. One aspect of the D800 is more "chatter" from
>the AF system than my D300 ever had, I commented on it here in
>another thread. It rarely seems to quite settle in, even in
>good light and normal subjects if you watch and listen, you
>hear it continually making tiny adjustments.


Are you using AF-C mode? I have never seen my D800 make any tiny adjustments in AF-S mode. Any chattering in AF-C could be due to any number of issues, movement of the subject, changing light, movement of the photographer, or even atmosphereic conditions (haze, heat etc.).

When I focus on any target with my D800 in AF-S, no matter how many times I defocus and focus, or just continually press the AF-ON button. The camera rarely makes an adjustment unless something has moved.

Try this sometime - put the camera on a sturdy tripod, turn on live view, and zoom in so the focus point takes up about half the screen. Observe how much movement there is when you put your hand on the grip to take a picture.

>I'm sure that is over-simplified, but as I said -- the
>comments ring true.
>
>Is it imprecise enough to matter? I'm happy with its
>precision. I get enough keepers to be satisfied, except with
>my 85/1.4 where the jury is still out.

I have noticed that after taking several shots in succession, each after a defocus-focus operation, that when viewing at 100% there are small variations. Are any of them out of focus? Yes, they all are. Nothing is ever in perfect focus. That said, are they what I would *perceptually* call out of focus? No, they are all acceptable. This is possibly where the D800s increased resolution may matter. The small, nearly imperceptible shot-to-shot differences that were once masked, are now becoming observable at 100%. This is all of course after having fine tuned the lens to a particular focus point. I don't think that this variation is increased from what older cameras produced, I just think it's more apparent.

Whether that percieved variation reduces the usefulness of a high resolution sensor, I'm not sure. At small apertures, it certainly does not. Wide open, maybe. But if you are shooting wide open, you aren't as concerned with image sharpness as you are shooting at f/5.6 or f/8 where the DoF will easily mask small shot-to-shot variation.

--
RL

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Hawk Eyes

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#24. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 0

Hawk Eyes Registered since 09th Jun 2012
Fri 17-Aug-12 03:35 PM | edited Fri 17-Aug-12 04:01 PM by Hawk Eyes

Haa haa, I challenge any one in the world who thinks the D800/D800E has any Auto focus Accuracy or precision Issues. Lets breakout out the action photos. I shoot the hardest sports in the world when it comes to shooting photos with my D800E, and I like how he throws the 1.4 prime in there haa haa to funny. Lloyd , Floyd , Fred , Ned bring them all on. Only thing is, I have photos to back my BS =)

ericbowles

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#25. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 24

ericbowles Moderator Awarded for his in-depth knowledge and high level skills in various areas, especially Landscape and Wildlife Photoghraphy Writer Ribbon awarded for for his article contributions to the community Donor Ribbon awarded for his very generous support to the Fundraising Campaign 2015 Nikonian since 25th Nov 2005
Fri 17-Aug-12 03:59 PM

I think it's a good idea, but let's create a separate thread for action photos with the D800/E.

This one started by Tristan is specifically about Lloyd Chambers comments.


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Hawk Eyes

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#26. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 25

Hawk Eyes Registered since 09th Jun 2012
Fri 17-Aug-12 04:08 PM | edited Fri 17-Aug-12 04:21 PM by Hawk Eyes

Good idea about starting the action thread. There are some good action shooters here in the D800 forum. I saw the hole article, it does not matter if it is a 1.4 prime or any prime I own now. I disagree completely.

Ferguson

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#27. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 23

Ferguson Silver Member Fellow Ribbon awarded for the generous sharing of his high level expertise in the spirit of Nikonians Nikonian since 19th Aug 2004
Fri 17-Aug-12 07:08 PM

>>I have a D800 and like
>it, but a lot of Lloyd's comments ring
>>true. One aspect of the D800 is more "chatter"
>from
>>the AF system than my D300 ever had, I commented on it
>here in
>>another thread. It rarely seems to quite settle in, even
>in
>>good light and normal subjects if you watch and listen,
>you
>>hear it continually making tiny adjustments.

>
>Are you using AF-C mode? I have never seen my D800 make any
>tiny adjustments in AF-S mode. Any chattering in AF-C could
>be due to any number of issues, movement of the subject,
>changing light, movement of the photographer, or even
>atmosphereic conditions (haze, heat etc.).

Yes, but try it, don't take my word for it. Put it on a tripod and focus on a tree trunk in daylight. I'm not suggesting it should never happen (it should), but compare it to a D300 or something. It's more pronounced. Is it wrong? I do not know. I just said his comments rung true.

Does it make a practical problem? I don't think so, am quite happy.

>That said, are they what I would *perceptually* call out of
>focus? No, they are all acceptable.

I agree also (though "all" is perhaps an exaggeration). I said, I am happy. I just said that the issue with precision matches my experience, which is not the same as saying it causes me a problem.

>Wide open, maybe. But if you are
>shooting wide open, you aren't as concerned with image
>sharpness as you are shooting at f/5.6 or f/8 where the DoF
>will easily mask small shot-to-shot variation.

Let's say you shouldn't expect the same sharpness, I won't give you that I am not concerned. To be precise, I want as accurate of a focus as I can get.



Linwood

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lukaswerth

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#28. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 26

lukaswerth Registered since 24th May 2012
Sat 18-Aug-12 07:43 AM

Well, coming to think of it: I read the extensive reviews on luminous landscape and dpreview, and they did not find any issues; particularly the LL one found praising words (and images to show!) for the d800's AF.

Lukas

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ljordan316

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#29. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 6

ljordan316 Silver Member Nikonian since 10th Feb 2010
Sat 18-Aug-12 08:06 AM | edited Sat 18-Aug-12 08:08 AM by ljordan316

While AF fine tuning all of my Nikon lens with two of my D800/E bodies, I also captured the AF consistency using the FoCal software. The results are shown below.

Click on image to view larger version


Note that consistency was really good for all lens, but it did drop some when I installed the 1.4x TC, probably due to mirror slap vibration.

Attachment#1 (jpg file)

Larry Jordan

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Ferguson

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#30. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 29

Ferguson Silver Member Fellow Ribbon awarded for the generous sharing of his high level expertise in the spirit of Nikonians Nikonian since 19th Aug 2004
Sat 18-Aug-12 10:22 AM

>While AF fine tuning all of my Nikon lens with two of my
>D800/E bodies, I also captured the AF consistency using the
>FoCal software. The results are shown below.

I recall you posting that before, and I had run that routine as well (but don't have access to my results now, on the road).

What is the thing being measured here? I.e. what is the 96.7% on the first. The consistency run does multiple images at the same scenario, defocusing and refocusing each time, and measures a quality of focus number on each. So you get (say) 10 numbers. How are you (or it?) turning it into a percentage in terms of the math?

Not taking issue with the numbers -- been saying it works well for me. But would be curious to see the same measurements with a D300 or D700, have you tried that?

But am asking about the math - I usually view precision as measured by something like standard deviation not percentage, so not sure how to interpret the number.

Linwood

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ljordan316

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#31. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 30

ljordan316 Silver Member Nikonian since 10th Feb 2010
Sat 18-Aug-12 11:05 AM

I agree re standard deviation about a norm for statistical work. I always used that during tests when I did that kind of engineering work.

The Focal 1.5.1 manual says the AF Consistency Test (available only in the Pro version) "allows you to review the consistency of the AF system of the camera across a number of identical shots."

You are allowed to change settings for the test:
- Defocus method (between each shot to ensure AF runs the full cycle)
- Test ISO
- Number of test shots

You can also select to run the test for a single AF Fine Tuning (FoCal calls it AFMA)or for a range of AFMA values that you choose. I ran all of my tests at the AFMA that I made during the AF Fine Tuning procedure. I really don't know why you want to do otherwise.

You can also choose to lock the mirror up during the tests. I did not check that box which may have resulted in my lower results with TC installed. I did not check the Mirror Lockup box because I seldom shot that way.

In another settings table, you can select to have the target image optimised. That eliminates any target movement cause by actual target movement or camera/lens movement. I did not select for target optimization. That might have increased my results for the longer lens and with TC installed.

The percentage value they provide at the end of the test is a peak-to-mean Quality of Focus (QoF) ratio expressed as a percentage. They take the mean QoF from all shots and divide by the best QoF taken during the series of shots. By comparing the mean to the best QoF, FoCal is eliminating the influence of lighting and quality of target as well as distance to target. The percentage is a relative number.

Because of the way they calculate the AF Consistency, the results would become more accurate as you increase the number of test shots. I always used 10 because that is their default value.

The manual gives an example that has an AF Consistency of 98.3% which they describe as good. The report you can save shows that Consistency of Focus score, but it does not rate the score as excellent, good, bad etc. I guess you have to decide for yourself what it means.

You can see the results on a graph which shows the QoF of each shot taken. You get to see the results of each shot so you calculate your own mean and standard deviation from those numbers. I did not do that.

I had already sold both of my D300 bodies before I started using FoCal, so I could not compare the results with non-D800 bodies. I believe Pete Beckett did compare results between D800 and D4 bodies. Maybe he will share his results.

One caveat with comparing results from different bodies however. Rich at FoCal says the FoCal results are not currently designed for body-to-body comparison...in an absolute quality sense. Apparently, that will be available in version 2.0 sometime next year.

Larry Jordan

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ericbowles

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#32. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 29

ericbowles Moderator Awarded for his in-depth knowledge and high level skills in various areas, especially Landscape and Wildlife Photoghraphy Writer Ribbon awarded for for his article contributions to the community Donor Ribbon awarded for his very generous support to the Fundraising Campaign 2015 Nikonian since 25th Nov 2005
Sat 18-Aug-12 11:36 AM

Larry's work with FoCal helps to illustrate the challenges with Lloyd's comments.

Based on the chart of FoCal results, the D800 appears to be more consistent than the D800E. But in the subsequent discussion and evaluation, that's not the full story.

Consistency does not measure quality of focus. If you were able to measure a higher resolution on the D800E, the test would have the ability to resolve more detail and report lower consistency but at a higher level of sharpness. If your complaint is precision - as is Lloyd's comment - sharpness was not the issue.

One of the uses of FoCal is to fine tune a lens. I would expect the chart reflects a lens calibrated on both cameras. In theory, calibration might or might not affect consistency depending on the amount and direction of the fine tuning. Another use of FoCal is to measure accuracy by sensor - and they are all a little different with the highest quality in the center on most lenses.

We've got a couple of good threads that discuss the FoCal system and results. But it does point out the separate dimensions of quality that are involved. Ideally you want a tight distribution of AF results with small and infrequent missed focus, you want the average focus to be correct - neither front or back focused, and you want the highest resolution possible.

By the way - I've read some recent articles on the accuracy of Phase Detect vs. Live View. While Live View is more accurate, there has been a trend toward improving Phase Detect to the point where the difference in accuracy vs. Live View is minimal.


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Ferguson

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#33. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 31

Ferguson Silver Member Fellow Ribbon awarded for the generous sharing of his high level expertise in the spirit of Nikonians Nikonian since 19th Aug 2004
Sat 18-Aug-12 12:44 PM

>The percentage value they provide at the end of the test is a
>peak-to-mean Quality of Focus (QoF) ratio expressed as a
>percentage. They take the mean QoF from all shots and divide
>by the best QoF taken during the series of shots. By comparing
>the mean to the best QoF, FoCal is eliminating the influence
>of lighting and quality of target as well as distance to
>target. The percentage is a relative number.

Thank you. That's an excellent example of why this stuff is hard. I faked some data by way of an example. The left column is perfect, the next shows a case where one shot is a wild outlier, the next shows a very good consistency but not perfect.

Both give 95% by Focal's technique, but the middle shows a case of operating outside of a control limits, and the other is operating inside control limits. I think from a real world application standpoint, one might label the right more precise than the middle, as it is consistently good.

I do not mean to imply that the camera is doing either one of these things, just that how complicated comparing ones experiences and testing are, how easily a specific aggregation or result total can mislead.


Test 1101010
Test 210109
Test 3101010
Test 410109
Test 510510
Test 610109
Test 7101010
Test 810109
Test 9101010
Test 1010109

Mean109.59.5
Peak101010
Mean/Peak100%95%95%
Std Dev0.01.50.5


I continue to say I am generally happy with the D800 performance, my one challenge (other than calibration on the left side) is with the 85/1.4G, where I do feel like it is pretty inconsistent. I wish I still had my D300 to test again. I can try against the D4, but it's got a very similar AF system.

Linwood

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ljordan316

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#34. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 32

ljordan316 Silver Member Nikonian since 10th Feb 2010
Sat 18-Aug-12 03:18 PM

>Based on the chart of FoCal results, the D800 appears to be
>more consistent than the D800E. But in the subsequent
>discussion and evaluation, that's not the full story.
>
>Consistency does not measure quality of focus. If you were
>able to measure a higher resolution on the D800E, the test
>would have the ability to resolve more detail and report lower
>consistency but at a higher level of sharpness. If your
>complaint is precision - as is Lloyd's comment - sharpness was
>not the issue.

You are right. While the AF consistency was a little lower with the D800E bodies than the D800, the reported Quality of Focus (QoF) or sharpness was about 45% higher across all apertures with the same lens on the D800E bodies than the D800 body, but keep in mind that Rich at Reikan says such body-to-body QoF comparisons are not valid with ver 1.5.1 of FoCal. IMHO, I believe it is a good indicator of body-to-body focus quality if you keep all test conditions constant even if the FoCal tests are not currently designed for that purpose.

>One of the uses of FoCal is to fine tune a lens. I would
>expect the chart reflects a lens calibrated on both cameras.

I ran the AFMA calibration on a body for a lens and immediately ran the Aperture Sharpness and AF Consistency test with that same body/lens. Thus, the results of those tests were the best the body could do with that lens under the target conditions at that time.

>In theory, calibration might or might not affect consistency
>depending on the amount and direction of the fine tuning.

I believe that is why you have an option of running the AF Consistency test at multiple AF Fine Tune settings. By doing that test, you could see where you get the most consistent focus. I would think the results of that test would be consistent with the AFMA calibration, but I never did that comparison.

>Another use of FoCal is to measure accuracy by sensor - and
>they are all a little different with the highest quality in
>the center on most lenses.

All of my AF Consistency tests were run using the center sensor. However, my Multi Point Sensor Test actually showed another sensor as being slightly better. For all three bodies I tested, the best sensor was at or near number 35...left and above center.

Larry Jordan

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ljordan316

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#35. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 33

ljordan316 Silver Member Nikonian since 10th Feb 2010
Sat 18-Aug-12 03:32 PM

I looked at the QoF data for several body/lens combinations and concluded that standard deviation calculations would not tell you anything for FoCal results unless you relate that number back to the mean QoF. The reason I say that is because Rich at Reikan says the QoF numbers are meant to be used as relative measures for a single body/lens/target combination. If you calculated the standard deviation for a set of AF consistency QoF points, you could only say that the deviation was for that test because the QoF results are relative.

If you divided the standard deviation by the mean QoF and quoted that as a percentage, then you would have a valid number because the division accomplishes the same thing the AF Consistency percentage accomplishes. It would show the deviation percentage from the mean regardless of the actual mean QoF. That would allow you to compare consistency results between camera bodies that produce different QoF results under identical target conditions. (Am I thinking straight here Pete?)

Larry Jordan

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critidoc

Kingsville, US
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#36. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 28

critidoc Silver Member Nikonian since 27th Feb 2007
Sat 18-Aug-12 05:04 PM

I am on my second D800 with the focus sensor problem. This time the right side is worse than the left. Nikon service suggests either exchanging it or trying to fix this one after they looked at the photos and reikan focal sensor map.
DSoes anyopne know if the D800E has these problems, hate to exchange it for another D800 with the same issue

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ljordan316

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#37. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 36

ljordan316 Silver Member Nikonian since 10th Feb 2010
Sat 18-Aug-12 05:06 PM

The D800E bodies I received from Adorama and Samy's do not have off-center focus issues. The sensors are not all the same, but none are below acceptable. I can send you my FoCal 51-point sensor test results if you want to see them.

Larry Jordan

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ljordan316

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#38. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 30

ljordan316 Silver Member Nikonian since 10th Feb 2010
Sat 18-Aug-12 05:46 PM

I just did a spreadsheet for the AF Consistency number I recoirded for my 50mm f/1.8. FoCal reported a Consistency of Focus of 98.4% on one of my D800E bodies. Using statistical analysis, the mean QoF for the lens was 1169.3 with a St Dev of 9.4 which is 0.8% of 1169.3.

For my 24-70mm set at 50mm, FoCal reported a Consistency of Focus os 96.7. The mean QoF was 1459.9 with a St Dev of 43.7 which is 2.9% of the mean.

From these two samples, it appears the Consistency of Focus results are a good indicator of the standard deviation you would get from the data. I am thinking you could calculate either for all of your lens on a given body and come to the same conclusions regardless of which method you use. The Consistency of Focus is probably easier for most folks to grasp since they can relate it directly to 100% being perfect.

From either method, I know my 50mm is more consistence in AF than my 24-70mm.

At what point would I declare a lens unfit? That is the question.

My 200-400mm had the lowest score of 93.7% on any D800/E body without target optimization turned on. I probably would have guessed that from the results I get in the field. I doubt I will get rid of the lens based on either the test or the field results. I know some shots will not be in focus, but most are.

If I had test results on a lens that showed an AF Consistency of 70% and I had problems getting crisp images in the field, I would probably dump it quick. Fortunately, my good Nikon glass does not show such an issue.

Larry Jordan

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ericbowles

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#39. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 38

ericbowles Moderator Awarded for his in-depth knowledge and high level skills in various areas, especially Landscape and Wildlife Photoghraphy Writer Ribbon awarded for for his article contributions to the community Donor Ribbon awarded for his very generous support to the Fundraising Campaign 2015 Nikonian since 25th Nov 2005
Sat 18-Aug-12 07:25 PM

Interesting, Larry.

I think I interpret those results to mean there is more variability with the 24-70, but even with 3 standard deviations in a negative direction (covering 99% of the time), QOF is better on the 24-70 than the 50. So even though the 50 is more consistent, it's not as sharp. Of course there are other reasons to use it.

That's not exactly true as you have previously reported that you can't truly compare lenses and cameras.

Am I interpreting the results properly?

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ljordan316

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#40. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 39

ljordan316 Silver Member Nikonian since 10th Feb 2010
Sat 18-Aug-12 08:01 PM

Yes. If everything were constant except the change from 50mm to 24-70mm lens (e.g. lighting on target and distance to target) and QoF is higher for the 24-70mm even with more variability of AF results, then I would prefer to use the 24-70mm because the FoCal tests show higher sharpness than the 50mm even when focus is not perfect. I have validated that difference in sharpness by looking at the target images that are captured by FoCal.

However, Rich at Reikan says that when you switch lens on the same body with all else held constant, you are still changing the target conditions...and thus cannot compare the results. Since I do not see how his tests actually operate in the software, I cannot comment on the validity of his statement. He may be splitting hairs while I am splitting logs.

When I see a 20-40% difference in QoF results when nothing changed but the lens, then I believe there is fire where I see this smoke. I felt the same when nothing changed but the body between a D800 and D800E. Thus, I sold my D800 and bought another E. When Rich finishes version 2.0 of FoCal next year, someone will invariably run the same test I ran and tell me whether I wasted my time and money switching bodies.

Since it only cost me a few hundred $$ to sell my D800 and I had used it for three months, I don't care how the body-to-body tests come out with ver 2.0. I know the E will not be less sharp than the D800.

Larry Jordan

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Lthole

Evergreen, US
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#41. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 0

Lthole Gold Member Nikonian since 16th Feb 2006
Sun 19-Aug-12 06:23 PM

I have found this to be a very interesting thread all in all it has covered most of the possible with the later half bring up the "real world" conditions. Using a 85 at 80 feet at 1.4 really, that is to me like using a 600 at a mile away hillside critter and wondering why some images missed. I also question using the lcd on the camera to make judgements. They are camera created jpgs not pure data.
On the precision side if you were doing product images or perhaps scientific imaging some of these repetitive issues might come into play, but don't all photographers in those fields check there work? Also just checking a dof app the 84 1.4 at 80ft show around 25 ft so what is point it trying to question a red bracket in the viewfinder vs the field of view and dof?

Dave

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Ferguson

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#42. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 41

Ferguson Silver Member Fellow Ribbon awarded for the generous sharing of his high level expertise in the spirit of Nikonians Nikonian since 19th Aug 2004
Sun 19-Aug-12 07:19 PM

>Using a 85 at 80
>feet at 1.4 really, that is to me like using a 600 at a mile
>away hillside critter and wondering why some images missed. I

Also just checking a dof app the 84
>1.4 at 80ft show around 25 ft so what is point it trying to
>question a red bracket in the viewfinder vs the field of view
>and dof?

I'm still confused why people have a negative reaction to the 85 at 80'. Why can't one decide, say for street photography or concerts, to use a 1.4/85 at 80'. It's not a portrait, but it seems a great application to me. With 25' DOF, imagine being face on to the concert stage, that nicely covers all the musicians, and even from the side gets one or two nicely in focus. When Flash is banned, with poor stage lights, that seems like an ideal combination. If it had consistent focus (which mine does not seem to -- I really need to try the D4 in this circumstance, will as soon as there's an outdoor concert!)

If my math is right, the 85 on an FX body at 80' gives you 28' high by 43' wide. Kind of big for a stage, but get down to 40-50' and it's just about perfect. Or crop -- there's plenty of pixels.

Everyone thinks "F1.4 - must be portraits". I think "need more light". I loved it with my D300, I have yet to get happy with the D800 and using it. Will see when the D800 comes back.

This is about a half frame crop on the D800, 85/1.4 @ 1.4, guestimate the distance at 35' or so, ISO 1600. If I had used the 70-200 @ 2.8 instead (a more normal choice), I would have been able to use more of the frame, but my ISO would have been 6400, and a lot less clean.




Linwood

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nikonus

Southern California, US
503 posts

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#43. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 0

nikonus Gold Member Donor Ribbon awarded for his generous support to the Fundraising Campaign 2014 Nikonian since 04th Feb 2007
Sun 19-Aug-12 11:10 PM

Back to just settings , I think some haven't set the AF from single to continuos . Page 92 in the manual . I've talked to a few who thought all they had was manual or AF with the lever under the lens .

Hans K.

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ljordan316

Inverness, US
830 posts

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#44. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 37

ljordan316 Silver Member Nikonian since 10th Feb 2010
Thu 23-Aug-12 10:32 AM

I can see from a note I just received that contains a FoCal 51-point sensor test report that some of you have trouble reading and understanding that FoCal report. When you look at one of those reports, remember that every sensor will not have the same QoF. Some will produce higher results that others. Also, keep in mind that the QoF values are meant to be relative numbers...not absolute readings of your focus sensor capabilities.

I understand from a note I received a few weeks ago from Rich at FoCal that his plans are to have a more robust QoF capability in version 2.0 and beyond which may happen in early 2013. If he can achieve that capability, then you will be able to compare camera bodies based on his QoF results. Right now the QoF can change easily as you change target lighting, distance to target or other variables. He plans to remove some or all of the QoF dependence on such variables.

I applaud Rich's pursuit. I understand that the Software Development Kits (SDK) from Nikon and Canon are not fully supported kits. That means the vendors do not provide full documentation for them, and could change their functionality without notice. People like Rich who build on those SDKs are taking some risk that Nikon or Canon could pull the rug out from under them at any time. So far, I do not believe that has happened, but it could.

IMHO, I believe Nikon and Canon will enhance their support of the SDKs in the future as more software companies start to use them for AF as well as other work. I believe Lightroom uses the SDKs functionality to perform tethered operations.

Pressure from users like you could result in enhanced support by Nikon for their SDK.

Larry Jordan

D800E, D500, 14-24, 16-35, 24-70, 70-180 Micro, 80-400mm AF-S, 500mm AF-S II

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moizes

Brooklyn, US
1322 posts

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#45. "RE: Auto Focus Accuracy and Precision for the D800/D800e" | In response to Reply # 18

moizes Silver Member Nikonian since 19th May 2006
Fri 24-Aug-12 09:09 AM

>I do not see much worth in Lloyd Chambers' comments. How do
>they relate to real life? Real life being the final product.
>
>
>All things have variances in precision and accuracy. The
>higher the
>level of precision the more costly the product. The higher the
>level of accuracy, the more costly the product. Because there
>is no perfect, there must be case of "good enough"
>for the associated cost.
>
>
>Good enough in the clarity of a photograph is often described
>in the depth of field, which is ultimately based on the final
>product.
>Since Depth of field is computed based on the Circle of
>Confusion, which is based on the final product - until you
>define the latter there is no logical discussion that can be
>meaningful. I did not see that in Lloyd Chambers' writings.
>
>
>And then terminology needs to be clearly understood, average
>does not necessarily equal the means and vice vera. A standard
>deviation or Sigma is often misunderstood. When dealing with
>variances, understanding what standard deviation is, and when
>it is proper to use (and maybe even more important when not to
>use) standard deviations are significantly important. A
>standard deviation is not a means of measurement but a
>representative number of the variance(s) involved. And without
>enough samplings, a determined standard deviation is
>worthless.
>
>
>It is all too easy to say things should be more accurate or
>have more precision, but till those are defined in real world
>outcomes and results, stating levels of precision and
>accuracy without knowledge in the affects is detrimental.
>Accuracy and precision can both be improved, but it comes at a
>cost!
>
>
>Lloyd Chambers comments may represent his data truthfully, but
>his data by itself is not significant enough to base any
>theories or determinations on.
>
Indeed. Agreed with every word, without reservations. That is what I wanted to say, unneccessary now! Yes, reality is the best judge of everything, including photography. THX! Dimitri.

G