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Subject: "another back focus question" Previous topic | Next topic
micro Silver Member Nikonian since 30th Mar 2008Thu 09-May-13 11:18 PM
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"another back focus question"


walkertown, US
          

let me start by saying that this is not a complaint or a rant. I'm just trying to get some understanding. I do not understand why all cameras that have focus fine tune actually need to be tuned with almost all lenses in existence but cameras that don't seem to be spot on with the same lenses. what do all the people that do not have really nice, very sturdy tripods do to be able to adjust focus and use their new camera? Is there a method to use that does not require a tripod? My tamron 70-200mm is extremely sharp from one end to the other on both of my d-80's.on my d-7000, I seldom get a keeper. Is there a specific reason that these cameras do not focus perfectly out of the box? Thanks, Troy

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Subject Author Message Date ID
Reply message RE: another back focus question
doppler_fto
10th May 2013
1
Reply message RE: another back focus question
JosephK Silver Member
10th May 2013
2
Reply message RE: another back focus question
km6xz Moderator
10th May 2013
3
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Escaladieu Silver Member
10th May 2013
4
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micro Silver Member
10th May 2013
5
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DaveSoderlund Silver Member
10th May 2013
6
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micro Silver Member
11th May 2013
7
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FLRuckman
12th May 2013
8
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briantilley Moderator
12th May 2013
9
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FLRuckman
13th May 2013
10
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briantilley Moderator
13th May 2013
11
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FLRuckman
13th May 2013
12
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km6xz Moderator
15th May 2013
15
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chuhsi
15th May 2013
13
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briantilley Moderator
15th May 2013
14
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micro Silver Member
15th May 2013
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micro Silver Member
27th May 2013
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doppler_fto Registered since 23rd Mar 2013Fri 10-May-13 03:43 AM
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#1. "RE: another back focus question"
In response to Reply # 0


US
          

>let me start by saying that this is not a complaint or a
>rant. I'm just trying to get some understanding. I do not
>understand why all cameras that have focus fine tune actually
>need to be tuned with almost all lenses in existence but
>cameras that don't seem to be spot on with the same lenses.

I'm not entirely sure what you mean here, but I don't think it changes the answer much:

There are two primary methods of autofocus: phase-detect AF, and contrast-detect AF.

For phase-detect AF, the camera has a separate autofocus sensor (which usually lives below the mirror-box). These cameras will also have a mirror which does double duty. The mirror reflects light upward to the optical viewfinder, and also downward toward the AF sensor.

Because the AF sensor lives in a different spot than the sensor, it's possible for the AF sensor to believe that the image is focused, when the image is actually slightly out-of-focus at the sensor. AF fine-tune tells the AF sensor to adjust its measurement of "in-focus" to match the actual location of the sensor.

For contrast-detect AF, the camera uses image-processing techniques on the image sensor itself to determine when the subject is in focus. Because it's using the data straight from the sensor, if the image "appears" in focus (and it's not just the algorithm messing up), then the image is necessarily in focus. There's only one place to check focus rather than two.

There are some cameras with hybrid AF. These cameras often have phase-detection AF sites on the image sensor, plus they will also use some contrast-detect AF algorithms. Theoretically, this allows them to rack focus quickly (with phase-detection), and then assure accurate focus (with contrast-detection). Plus, since the phase-detection sites actually live on the image sensor, these kinds of cameras shouldn't require AF fine-tuning.

Finally, it seems you may be talking about DSLRs that do not feature AF fine-tune, but which do use phase-detect AF. If they are not hybrid systems, then they will be susceptible to small autofocus errors. It's just that you can't correct them.

>what do all the people that do not have really nice, very
>sturdy tripods do to be able to adjust focus and use their new
>camera? Is there a method to use that does not require a
>tripod? My tamron 70-200mm is extremely sharp from one end to
>the other on both of my d-80's.on my d-7000, I seldom get a
>keeper. Is there a specific reason that these cameras do not
>focus perfectly out of the box? Thanks, Troy

Do you have a specific example of what kind of problems you're seeing? "I seldom get a keeper" isn't a very precise description, and it's not much to go on as far as troubleshooting is concerned.

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JosephK Silver Member Nikonian since 17th Apr 2006Fri 10-May-13 06:02 AM
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#2. "RE: another back focus question"
In response to Reply # 0


Seattle, WA, US
          

Here is a good article that will give you an idea about what is going on:
http://www.lensrentals.com/blog/2008/12/this-lens-is-soft-and-other-myths

---------+---------+---------+---------+---------+
Joseph K
Seattle, WA, USA

D700, D200, D70S, 24-70mm f/2.8, VR 70-200mm f/2.8 II,
50mm f/1.4 D, 70-300mm f/4.5-5.6 VR, 18-70mm f/3.5-4.5 DX

  

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km6xz Moderator Awarded for his in-depth knowledge in various areas, including Portraits and Urban Photography Nikonian since 22nd Jan 2009Fri 10-May-13 06:11 AM
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#3. "RE: another back focus question"
In response to Reply # 0


St Petersburg, RU
          

Before giving advice on how to improve your keeper rate, can you post some typical photos that display the focus problem?
Most often the cause of AF inaccuracies with new cameras is getting used to the settings and how the camera responds. Do you notice the same problem with other lenses?
Stan
St Petersburg Russia

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Escaladieu Silver Member Nikonian since 18th Apr 2010Fri 10-May-13 07:49 AM
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#4. "RE: another back focus question"
In response to Reply # 0


Artiguemy, FR
          

>let me start by saying that this is not a complaint or a
>rant. I'm just trying to get some understanding. I do not
>understand why all cameras that have focus fine tune actually
>need to be tuned with almost all lenses in existence but
>cameras that don't seem to be spot on with the same lenses.
>what do all the people that do not have really nice, very
>sturdy tripods do to be able to adjust focus and use their new
>camera? Is there a method to use that does not require a
>tripod? My tamron 70-200mm is extremely sharp from one end to
>the other on both of my d-80's.on my d-7000, I seldom get a
>keeper. Is there a specific reason that these cameras do not
>focus perfectly out of the box? Thanks, Troy


Maybe your shutter speed is too low - you can quickly test if your lens / body combination needs adjustment by taking a few shots with flash - images should be sharp - if they are, its likely your technique (without flash) that is at fault, if not then perhaps adjustment is needed - investigate further.

Personal Blog
www.gasconyphoto.net

  

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micro Silver Member Nikonian since 30th Mar 2008Fri 10-May-13 10:19 AM
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#5. "RE: another back focus question"
In response to Reply # 4


walkertown, US
          

let me re-phrase my question. does a d-7000 use a different way of focusing compared to a d-80 causing the need to fine tune focus? my other question was, do I need a very nice,sturdy, more costly, higher end tripod in order to perform fine tune adjustments? thanks, Troy

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DaveSoderlund Silver Member Nikonian since 29th May 2010Fri 10-May-13 01:05 PM
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#6. "RE: another back focus question"
In response to Reply # 5


Geneva, US
          

Troy,

Let me take crack at your two re-phrased questions.

First, the ability to perform focus fine tuning in the camera requires the ability to compare the performance of the autofocus sensor and Live View focusing at the camera sensor itself. If I remember correctly, the D80 does not have Live View focusing, so the only way to tell if a D80 or similar camera is exhibiting focus tuning problems with a particular lens is to set it up with a series of focus targets, focus on them, inspect the image, and decide if the sharpest part of the image corresponds to the nominal point of focus.

Second, you don't need a "big, expensive tripod" to do this. All you need is absolutely rock-solid camera support (and a remote release) to ensure that camera shake is removed from the analysis. An ancient but sturdy tripod would work fine, as would a 3-lb bag of rice on a table.

The high pixel density of the D7000 and later cameras is very unforgiving, because the sensor will detect camera movement that lower density sensors could not. Many folks here at Nikonians who moved to the newest generation of cameras (esp. D7000, D7100 and D800) have reported the need to use higher shutter speeds (even with VR) and the best hand-holding techniques to eliminate the camera movement that had been undetectable previously with their old cameras. My brief experience, so far, of moving from the D90 to the D7100 confirms this -- as long as I don't get too greedy by trying to hand-hold at low shutter speeds I get very sharp pictures.

Finally, the article from LensRentals that is linked above is really helpful. I particularly appreciate the observation that the need for focus fine tuning becomes really obvious with fast prime lenses shot wide open, where the plane of focus is extremely thin. I haven't rigorously tested my D7100 with either of my fast prime lenses (35mm f/1.8; 50 mm f/1.8) to see if there is any discrepancy between autofocus sensor and Live View focusing.

Dave

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micro Silver Member Nikonian since 30th Mar 2008Sat 11-May-13 11:55 AM
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#7. "RE: another back focus question"
In response to Reply # 6


walkertown, US
          

Thanks everyone for your replies and that link to lens rentals. I'm getting a better understanding about how it all works. It's hard to test and adjust when I do not understand just how it all works together. I need to upgrade my tripod some day as the one I have is basically worthless. very unstable. I've noticed that just someone walking around in my house causes vibrations up thru my tripod into the camera. I will look for a beanbag or bag of rice for now. Thanks again for the help, Troy

there is no problem to big or small that can't be fixed with brute strength and ignorance visit my gallery

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FLRuckman Registered since 02nd Apr 2013Sun 12-May-13 12:51 PM
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#8. "RE: another back focus question"
In response to Reply # 6


Collinsville, US
          

First, I'm not a highly experienced photographer. Recently sold my D80/18-200 combo and replaced with D7100 and better glass (35 and 50mm 1.8 primes and preowned 12-24 f4). I've thoroughly enjoyed the low-light capabilities of these primes when shooting my new grandson indoors. But, I frequently find that each lens will occasionally focus hunt even though the lighting seems adequate. Is this an indication that fine tuning is needed? Or, something else? Thanks!

  

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briantilley Moderator Deep knowledge of bodies and lens; high level photography skills Nikonian since 26th Jan 2003Sun 12-May-13 01:09 PM
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#9. "RE: another back focus question"
In response to Reply # 8


Paignton, GB
          

Focus hunting is not something that AF Fine Tune can help with.

Hunting can be caused by insufficient light - though in your case it sounds like that's not a problem - by using an AF target with low contrast, or by selecting inappropriate AF settings for the type of subject.

Another possibility is that the lack of VR on your three current lenses is allowing the scene to "dance around" a little in the viewfinder, so making it more difficult for AF to lock on.

Brian
Welsh Nikonian

  

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FLRuckman Registered since 02nd Apr 2013Mon 13-May-13 07:44 PM
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#10. "RE: another back focus question"
In response to Reply # 9


Collinsville, US
          

Thanks...I suspect you are right that subject movement might
be the cause.  I'll pay more attention next time.  Regarding
AF fine tuning, is this something that is recommended for all
lenses?  And, if yes, can you point me to a method for doing
so?

  

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briantilley Moderator Deep knowledge of bodies and lens; high level photography skills Nikonian since 26th Jan 2003Mon 13-May-13 08:22 PM
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#11. "RE: another back focus question"
In response to Reply # 10


Paignton, GB
          

I didn't mean that the subject was moving - although it may well be - but rather that, because it seems that you were used to a lens with VR and now your lenses don't have that feature, you may not be holding the camera steady enough for the focus system to get a clear lock on the target.

Some folks seem to enjoy employing AF Fine Tune on every lens, perhaps to make sure that everything is working at its peak. For myself, I have three cameras with that feature and quite a few lenses, and I've never needed to use it even once. It's really intended for use if you can clearly see a consistent focus problem in actual shooting.

You'll find quite a few discussions on AF Fine Tune using a variety of techniques and tools over in our D800 Forum - because a few examples of that camera had a particular problem with AF.

Brian
Welsh Nikonian

  

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FLRuckman Registered since 02nd Apr 2013Mon 13-May-13 08:41 PM
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#12. "RE: another back focus question"
In response to Reply # 11


Collinsville, US
          

At 64, the hands aren't as steady as they used to be. But, I have the new Nikon 80-400 (with VR of course) and am getting some great shots. Nikon seems to be slow in introducing VR in some of their inexpensive primes such as the 35 and 50mm.
Thanks again for your comments.
Hoping to visit your beautiful country next year for the first time.

  

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km6xz Moderator Awarded for his in-depth knowledge in various areas, including Portraits and Urban Photography Nikonian since 22nd Jan 2009Wed 15-May-13 09:11 AM
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#15. "RE: another back focus question"
In response to Reply # 11


St Petersburg, RU
          


>
>Some folks seem to enjoy employing AF Fine Tune on every lens,
>perhaps to make sure that everything is working at its peak.
>For myself, I have three cameras with that feature and quite a
>few lenses, and I've never needed to use it even once. It's
>really intended for use if you can clearly see a consistent
>focus problem in actual shooting
.

Brian makes a very good point. Lenses, cameras and lighting all interact to create differing results when any or all are changed. If a lens/camera combination are consistently focusing off, in all light color temperature and intensity, it is worth checking into more rigorous testing. But if it is noticed or suspected in just certain conditions or even many conditions AF Tuning will possibly make it worse by assuring those conditions where it was consistent will be consistently off after adjustment.
If the focus is predictably off all the time to the same degree in all light levels and color temperatures, an adjustment can be of benefit.
Test charts indoors are not the answer to whether your real world photos will be off or on. Many cameras compensate more than others for incandescent light temperatures by shifting focus more than others but they all do to a degree. You might make it worse by optimizing it for that indoor lighting.
CA for example is caused by the same refraction shift with color but in the case of the focusing sensor, that change with color is a real factor in what it detects as "in-phase", not just fringing on edges seen by the image sensor.
There is no perfect setting, the camera software makes a lot of informed nudges of mechanical systems to attempt to compensate for the changes with color so the optimum settings are those which are the best compromise in the widest range of conditions. Altering that balance of competing issues can hurt more than help.

Your first indication that testing should be done is seeing it in real work images over a wide range of conditions, not testing to see if there is a problem before seeing one in real photos.


Stan
St Petersburg Russia

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chuhsi Registered since 12th Mar 2013Wed 15-May-13 03:27 AM
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#13. "RE: another back focus question"
In response to Reply # 6


US
          

do you recommend any particular guidelines for shutter speed to minimize shake effets?

  

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briantilley Moderator Deep knowledge of bodies and lens; high level photography skills Nikonian since 26th Jan 2003Wed 15-May-13 08:06 AM
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#14. "RE: another back focus question"
In response to Reply # 13


Paignton, GB
          

With a high-MP DX camera like the D7000 and D7100, It's a good idea to keep the shutter speed at least twice the reciprocal of the focal length in use - in other words, if the focal length is 200mm (and you're not using VR), I'd try to use 1/400th as a minimum.

Brian
Welsh Nikonian

  

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micro Silver Member Nikonian since 30th Mar 2008Wed 15-May-13 10:27 PM
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#16. "RE: another back focus question"
In response to Reply # 14


walkertown, US
          

OK,so, I did lots of inside and outside testing with 3 different lenses. My Nikon 18-55mm VR focuses perfect and is very sharp. My sigma 24-70 F2.8 (older style) focuses perfect and is very sharp. My tamron 70-200mm F2.8 (which is my most favorite lens) consistently back focuses a lot and wont auto focus at all in live view. My other lenses work in live view so for that reason it is on it's way to tamron in NY. I also mentioned the back focus problem so they should at least check it's specs and hopefully I wont have to mess with fine tuning it,hope,hope,hope.It is still under warranty so no worries there. wish me luck. Troy

there is no problem to big or small that can't be fixed with brute strength and ignorance visit my gallery

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micro Silver Member Nikonian since 30th Mar 2008Mon 27-May-13 12:15 AM
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#17. "RE: another back focus question"
In response to Reply # 16


walkertown, US
          

Got my lens back. It is tack sharp again and works in live view. I,m guessing that it was not communicating properly with my D-7000 since it worked fine on my D-80's. It took me a while to figure out whether the issue was the new camera, the lens, or myself. Now I can get out and enjoy my new camera with my most favorite lens. Troy

there is no problem to big or small that can't be fixed with brute strength and ignorance visit my gallery

Visit my Nikonians gallery.

Visit my Nikonians gallery.

  

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