nikonians

Even though we ARE Nikon lovers,we are NOT affiliated with Nikon Corp. in any way.

| |
Go to a  "printer friendly" view of this message which allow an easy print Print Go to the page which allows you to send this topic link and a message to a friend Email this topic to a friend
Forums Lobby GET TO KNOW YOUR CAMERA & MASTER IT Nikon D90/D80/D70 (Public) topic #6258
View in linear mode

Subject: "D80 Backfocus (fixed)" Previous topic | Next topic
kocho Basic MemberWed 22-Nov-06 03:13 AM
1756 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
"D80 Backfocus (fixed)"


Metro DC, US
          

My brand new D80 had significant backfocus out of the box. Luckily, it is adjustable in what seems to be exactly the same way as the D70/D70s, so I was able to bring it to normal easily.

Just thought I'd share. You can search on the D70 forum here or on DPReview more on the issue if you need details.

My PBase Gallery Favorites

  

Alert Print | Reply | Quote | Top

Replies to this topic
Subject Author Message Date ID
Reply message RE: D80 Backfocus (fixed)
markscamera
23rd Nov 2006
1
Reply message RE: D80 Backfocus (fixed)
kocho
23rd Nov 2006
2
Reply message RE: D80 Backfocus (fixed)
bclaff Silver Member Awarded for multiple contributions for the Resources
23rd Nov 2006
3
Reply message RE: D80 Backfocus (fixed)
kocho
23rd Nov 2006
4
Reply message RE: D80 Backfocus - are you sure?
Len Shepherd Gold Member
24th Nov 2006
5
Reply message Len...
kocho
16th Jan 2008
15
     Reply message RE: Len...
bclaff Silver Member Awarded for multiple contributions for the Resources
25th Nov 2006
6
     Reply message Bill...
kocho
16th Jan 2008
          Reply message RE: Bill...
bclaff Silver Member Awarded for multiple contributions for the Resources
27th Nov 2006
8
          Reply message Update - backfocus is there.
kocho
28th Nov 2006
10
          Reply message RE: Bill...
bclaff Silver Member Awarded for multiple contributions for the Resources
27th Nov 2006
9
     Reply message "Real life" test
kocho
25th Nov 2006
7
Reply message RE: D80 Backfocus UPDATE
kocho
04th Dec 2006
11
Reply message RE: D80 Backfocus UPDATE
Len Shepherd Gold Member
05th Dec 2006
12
     Reply message Len,
kocho
16th Jan 2008
16
          Reply message RE: Len does listen
Len Shepherd Gold Member
07th Dec 2006
13
               Reply message RE: Glad to hear it :)
kocho
07th Dec 2006
14

markscamera Registered since 06th Aug 2006Thu 23-Nov-06 01:25 AM
1614 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#1. "RE: D80 Backfocus (fixed)"
In response to Reply # 0


Morristown, US
          

I have a D80 and I'm interested in the back focus adjustment. I don't think I have a problem but if I do I'd like to know more about it. Is this a DIY fix?
Mark
D80, D50, F100, F80s, N90s, F3HP, FM2n

Mark
east TN Nikonian

  

Alert Print | Reply | Quote | Top

    
kocho Basic MemberThu 23-Nov-06 03:00 AM
1756 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#2. "RE: D80 Backfocus (fixed)"
In response to Reply # 1


Metro DC, US
          

>I have a D80 and I'm interested in the back focus
>adjustment. I don't think I have a problem but if I do I'd
>like to know more about it. Is this a DIY fix?
>Mark
>D80, D50, F100, F80s, N90s, F3HP, FM2n

Search for backfocus and Leon Goodman. He has pictures of the D70 adjustment. It appears the D80 is the same. Read his write-up and the gotchas. He uses tape instead of the MLU fucntion to hold the mirror up - I think this way the mirror is up and the shutter is still closed, so less dust can enter to the censor compared to MLU method. Up to you I guess...

Theoretically very easy to do - just rotate little by little one 2mm hex screw that is behind the mirror (use MLU to lift the mirror). To compensate for backfocus you rotate up (when canera is in normal landscape position), for front focus - down. In practice, you need to have good target and patience as it is a trial and error process. Easiest to do it with the camera tethered to a computer so that you can see the results better and faster.

My PBase Gallery Favorites

  

Alert Print | Reply | Quote | Top

bclaff Silver Member Awarded for multiple contributions for the Resources Nikonian since 26th Oct 2004Thu 23-Nov-06 03:55 AM
9681 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#3. "RE: D80 Backfocus (fixed)"
In response to Reply # 0


Vancouver (WA USA not Canada), US
          

Mihail,

That's interesting news! I've never seen the insides of a D80.

You've probably seen what I did to my D70 (AF Sensor Nerdvana Achieved) following similar instructions.

Regards,
Bill

Visit me at My site

  

Alert Print | Reply | Quote | Top

    
kocho Basic MemberThu 23-Nov-06 04:25 PM
1756 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#4. "RE: D80 Backfocus (fixed)"
In response to Reply # 3


Metro DC, US
          

>Mihail,
>
>That's interesting news! I've never seen the insides of a
>D80.
>
>You've probably seen what I did to my D70
>(AF
>Sensor Nerdvana Achieved>) following similar instructions.
>
>Regards,
>Bill

Yes, about the same look and location of the two hex screws. Anyway, I will be exchanging the set I got as it is an early version with the worse amp glow problem. So I'll have the "pleasure" to test another sample probably tomorrow...

My PBase Gallery Favorites

  

Alert Print | Reply | Quote | Top

Len Shepherd Gold Member Nikonian since 09th Mar 2003Fri 24-Nov-06 05:15 PM
12722 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#5. "RE: D80 Backfocus - are you sure?"
In response to Reply # 0


Yorkshire, UK
          

If you were using a 45 degree test target or one of the 6 types of target where Nikon say AF may not work well the chances are probably higher than 99% you did not have back focus.
Over the last 5 months I have seen no allegations using good AF targets - and 101 using unsuitable for testing AF targets.
Over the years I have seen 2 proven cases due to a faulty AF block in early D2x which adjusting the cams would not sort out.
As yet I have seen no back focus issue with a D70, D70s, D200, or D80 using a reliable back focus detection method.
Yours might be the first using a reliable test method. If so perhaps you can post an image or explain how you did the test.

Photography is a bit like archery. A technically better camera, lens or arrow may not hit the target as often as it could if the photographer or archer does not practice enough.

Len Shepherd

  

Alert Print | Reply | Quote | Top

    
kocho Basic MemberWed 16-Jan-08 02:11 PM
1756 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#15. "Len..."
In response to Reply # 5


Metro DC, US
          

>If you were using a 45 degree test target or one of the 6
>types of target where Nikon say AF may not work well the
>chances are probably higher than 99% you did not have back
>focus.
>Over the last 5 months I have seen no allegations using good
>AF targets - and 101 using unsuitable for testing AF
>targets.
>Over the years I have seen 2 proven cases due to a faulty AF
>block in early D2x which adjusting the cams would not sort
>out.
>As yet I have seen no back focus issue with a D70, D70s,
>D200, or D80 using a reliable back focus detection method.
>Yours might be the first using a reliable test method. If so
>perhaps you can post an image or explain how you did the
>test.

Len,

If you want you can tell me (privately if you whish) what test specifically you would like me to do and I can retest. I returned my D80 as it turned out it was an early model with the tripple-source amp-glow that I did not like. I am on order for another one that will come early next week. When it is here I will be testing it anyway, so I might just follow your instructions to make sure I get good results.

For the very detailed test with many lenses on the D1x and D70s I deleted the images already. I actually started with a target that I used previously with good success with mid and telephoto lenses: a Mobil 1 Oil bottle with focus on the large print on the front - placed well infront of other objects. With the wider lenses however I thought that I might be leaving room for error as the edges of the bottle are tapered and I thought that it might be possible in some cases the camera to pick the contrast b/w the side of the bottle (which is 1/4 inch behind the front) and the dark background rather than the front label type. So I switched the target to the one described below that is essentially flat and not 3-D, but I got the similar results.

I also use the 45 degree test target that you can see below. Printed on a 11x17 inch paper. A larger size crop that is easier to see is here:

http://www.pbase.com/kocho/image/69905452/original

I find it very accurate and I know that my center censor is about 10% lower than it should be and that it extends about double the width of the central square in the viewfinder on the D70s. In focus-lock mode, I can only lock focus on the center line - just above or below it and it hunts on the white area around the line. I understand this target's limitations, so I always do a parallel target test if I have doubts. This particular shot below shows the 180mm AF-D I have when my D70s body was adjusted for it (all other lenses had relative backfocus on the same target or on the more precise parallel target tests). After adjusting the focus for the other lenses, the 180 AF-D started to front-focus as much so that I need at least F/5.6 or a little more to get the rear of the DOF to begin to cover the test target.

For the "more conclusive" test I used a 25cm by 25cm foam tile from a kids "learn the alphabet" mat. Colorful with good contrast b/w the letter and the surrounding area of the tile. It has a large colored number in the middle ocupying more than half the tile (I think I used the "O" or "S" or something like that so that the central censor had more than one spot to measure). The tile also has a decent texture plus some scratches from chairs and use, so it is easy to see whether it is sharp or not. The tile was parallel to the sensor, the camera was level to the center of the tile and the tile occupied almost the entire frame. The tile was placed so that it was about 3 feet infront of any other objects behind it. The tile was illuminated from about 50cm by a 250 watt fluorescent light so it was bright and the background was much darker. Took autofocus in AF-C mode (thru AF-ON button) then let go off the AF-ON button, and shot. Moved the camera back a little (on a tripod), then shot again without refocusing and so on. This was done for several lenses and the two bodies to make sure they behave consistently.

Once I was satisfied that things do look consistent, I was not really moving the camera back and fourth anymore. Instead relied more on the DOF position relative to the teeth of a big-toothed saw I have placed by the side of the tile and that was close to the edge of the frame (well outside of the central focus area which was the only one used). That is what I have listed in the "log" I posted earlier. Shots were from at least a couple of feet beyond the minimum focus distance of the lenses tested. Camera was positioned so that I got approximately the same frame coverage from the tile so that autofocus and detail would be very close (e.g. at 50mm the 18-200 VR was approximately 3-4 feet away, the 50mm AF-D about a foot or more farther away, the 180mm AF-D about 8-10 feet or so, the Sigma 10-20 was pretty close to the target, etc.)

I think the test was accurate because the D1x and the D70s showed very close performance in terms of focus with each lens tested, e.g. the D1x had slight backfocus with most lenses and showed slight front focus with the 180mm AF-D. My D70s things were just shifted back - the 180 was fine and all other lenses backfocused quite a bit but by similar pattern as they did with the D1x, just offset to the back more since it was already set to backfocus to compensate for the 180mm front focusing.

Finally, there is one more "quick and dirty" test target I made-up from a mail coupon and my daughter's sheet music under it. I think it is good as there is nothing else to lock focus on and the large print is good contrast and parallel enough to the sensor.

This is the entire frame, if I recall. This was shot from the 18-200 VR at 135mm, 1/100s, F/5.6 after adjusting my D70s for my other lenses (it now front focuses with the 180 AF-D but is fine with all others). The center crop from the same image is here:

http://www.pbase.com/kocho/image/70322923/original


Regards,
Kocho

My PBase Gallery Favorites

Attachment #1, (jpg file)
Attachment #2, (jpg file)

  

Alert Print | Reply | Quote | Top

        
bclaff Silver Member Awarded for multiple contributions for the Resources Nikonian since 26th Oct 2004Sat 25-Nov-06 05:15 AM
9681 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#6. "RE: Len..."
In response to Reply # 15


Vancouver (WA USA not Canada), US
          

Mihail,

I don't know if they are "Len approved" but here is a link to a couple of non-angled tests: RE: Sigma 30 1.4 focus errors.

FWIW, I think an angled test can work, they are just much more prone to error; but you seem to have taken a great deal of care in your test.

Regards,
Bill

Visit me at My site

  

Alert Print | Reply | Quote | Top

            
kocho Basic MemberWed 16-Jan-08 02:11 PM
1756 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
"Bill..."


Metro DC, US
          

Bill,

Thanks for the reply. I remember your threads, even though I did not go as far as to measure the standard deviation.

I got a replacement D80 today, this time with the 18-135 lens as kit. This one also seems to be backfocusing some. I'll be posting my findings in more detail once I get a chance to test more thoroughtly, but here is what it looks like with the "golden apple" test (that sounds good to me ). Got very similar results with three lenses on this quick test, so chances are the more careful testing would confirm this, but we'll see...

Thoughts?

Full frame and 100% crop are shown here (look at the stamps book edge), plus one more "visual" from a 45 degree test, where it is easier to see.

Am I doing it wrong? My test is IMO as good as it needs to be. Even if I'm not perfectly square, I'm still within the margin of error - the DOF shift is much more than any "non-squaredness" would cause. Plus by repeating it several times with different lenses at different focal lengts and getting similarly consistent results I think it is "good enough"...

Thanks!


>Mihail,
>
>I don't know if they are "Len approved" but here is a link
>to a couple of non-angled tests:
>RE:
>Sigma 30 1.4 focus errors>.
>
>FWIW, I think an angled test can work, they are just much
>more prone to error; but you seem to have taken a great deal
>of care in your test.
>
>Regards,
>Bill

My PBase Gallery Favorites

Attachment #1, (jpg file)
Attachment #2, (jpg file)
Attachment #3, (jpg file)

  

Alert Print | Reply | Quote | Top

                
bclaff Silver Member Awarded for multiple contributions for the Resources Nikonian since 26th Oct 2004Mon 27-Nov-06 09:44 PM
9681 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#8. "RE: Bill..."
In response to Reply # 0


Vancouver (WA USA not Canada), US
          

Mihail,

Assuming that the target was square with the camera then it looks like a slight back focus.
I'm not you but I think I would find this result acceptable.

Regards,
Bill

Visit me at My site

  

Alert Print | Reply | Quote | Top

                    
kocho Basic MemberTue 28-Nov-06 05:00 AM
1756 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#10. "Update - backfocus is there."
In response to Reply # 8


Metro DC, US
          

>Mihail,
>
>Assuming that the target was square with the camera then it
>looks like a slight back focus.
>I'm not you but I think I would find this result acceptable.
>
>Regards,
>Bill

I agree and my second test confirmed my casual observation - slight backfocus is present.

See this post for the image and details.

http://www.nikonians.org/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=19463&forum=DCForumID6

Used your standard deviation method (I hope correctly) to better judge the relative sharpness b/w images, but it is also obvious with careful pixel peeping which is the sharpest. My numbers may be off by one or so depending on where I measure but the relative results are valid.

Thanks,
Mihail

My PBase Gallery Favorites

  

Alert Print | Reply | Quote | Top

                
bclaff Silver Member Awarded for multiple contributions for the Resources Nikonian since 26th Oct 2004Mon 27-Nov-06 10:50 PM
9681 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#9. "RE: Bill..."
In response to Reply # 0


Vancouver (WA USA not Canada), US
          

Mihail,

Off Topic (OT) but take note of the following Opanda dump of the first image you provided in post#9.
The red values are wrong values reported by Opanda.
The green values are correct values.
On lines with only red or green then the other color is blank.
Curly braces are sued in the place of square braces due to the way Nikonians handles posts
The reason is one of several bugs in various version of Nikon Capture.
In this case the Makernote is incorrectly written.
So, beware!

Regards,
Bill

{Image}
Make = NIKON CORPORATION
Model = NIKON D80
Orientation = top/left
Software = Nikon Capture Editor 4.3.2 W
Date Time = 2006-11-27 13:13:07

{Camera}
Exposure Time = 1/200"
F Number = F5.6
Exposure Program = Manual
ISO Speed Ratings = 100
Exif Version = Version 2.21
Date Time Original = 2006-11-27 12:33:06
Date Time Digitized = 2006-11-27 12:33:06
Exposure Bias Value = ±0EV
Max Aperture Value = F5.66
Metering Mode = CenterWeightedAverage
Light Source = Flash
Flash = Flash fired, auto mode, return light detected
Focal Length = 135mm
Maker Note = 886 Byte
User Comment =
Subsec Time = 0.30"
Flashpix Version = Version 1.0
Color Space = sRGB
Exif Image Width = 799
Exif Image Height = 535
Sensing Method = One-chip color area sensor
File Source = DSC
Scene Type = A directly photographed image

{Thumbnail}
Thumbnail = 160 x 107

{MakerNote (Nikon)}
Makernote Version = 0210
ISO Speed Used = 100
Colour Mode = COLOR
Quality = H FINE
White Balance = FLASH
Sharpening = AUTO
Focus Mode = AL AF-C
Flash Setting = NORMAL
Auto Flash Mode = Built-in,TTL
White Balance Bias Value = 0
White Balance Red, Blue Coefficients = 10000000/1, 1/1, 1/0, 169873184/0
000D = 00, 01, 06, 00
Exposure Diff = CE, 01, 0C, 00
ThumbOffset = 868
Flash Compensation = 00, 01, 06, 00
ISO Speed Requested = 100
Photo corner coordinates = 1, 0, 0, 39040,0,3872,2582
AE Bracket Compensation Applied = +97803.96EV0
001B = 0, 12339, 12596, 13875, 49, 21825, 20308
001D = 3041361
001E = 1sRGB
Tone Compensation (Contrast) = AUTO
Lens Type = Nikon D series Lens
Lens Min/Max Focal Length, Max Aperture = 1/35, 10/56, 10/1162104653, 538992945/134761676818,135,7/2,28/5
Flash Used = Flash Fired
Auto Focus Area = 00, 00, 00, 01
Bracketing & Shooting Mode = 8
008A = 2
008B = 40, 01, 0C, 00
Colour Mode = EEDLIGHT MODE1a
Lighting Type = OFF SPEEDLIGHT
Hue Adjustmen = 0
Noise Reduction = OFF
009A = 100/0, 0/0121/20,121/20
009E = 0, 0, 0, 0, 20302, 19794, 19521, 0, 12592, 12336
00A2 = 29423
00A3 = 0
Total Number of Shutter Releases for Camera = 38
Image optimisation = NORMAL
Digital Vari-Program =
00B0 = 00, 00, 00, 00, 4E, 69, 6B, 6F, 6E, 20, 43, 61, 70, 74, 75, 72
00B1 = 0
0E08 = 1
0E10 = 962

Visit me at My site

  

Alert Print | Reply | Quote | Top

        
kocho Basic MemberSat 25-Nov-06 05:23 AM
1756 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#7. ""Real life" test"
In response to Reply # 15


Metro DC, US
          

Finally, this is what it looks in "real life" test. This of course is a target that one may argue is prong to errors and it is. I know that the DOF distribution you see here is reperesentative of the relative front-focus of the 180mm AF-D compared to, in this case, the 18-200 VR and is shown just for illustration, not as a conclusive test (the previous post describes how I did a more conclusive test).

These are full-sized images at about 700KB each, so they may be slow to load for some.

First photo:
18-200 VR at 200mm. DOF is distributed both infront and behind the center chimney. You can trace the DOF extending forward along the rooftop as well as on the roof behind the chimney where there is good sharpness as well. This is how it should be more or less, even though it is more to the back than I think the 1/3 vs. 2/3 roule specifies.
http://www.pbase.com/kocho/image/70719836/original

Second photo:
180mm AF-D at F/6.3. The rear of the DOF covers the target (the chimney in the front). But most of the DOF is infront of the chimney. You can trace the sharp area in the DOF extending forward along the rooftop all the way to the right of the frame (the black tin rail is sharp to the edge on the right).
http://www.pbase.com/kocho/image/70719839/original

Third photo:
For comparison, the same shot at F/2.8 with the 180mm AF-D. The DOF is now entirely infront of the target chimney (see the front shingles and the rail towards the right get sharper).
http://www.pbase.com/kocho/image/70719842/original

My PBase Gallery Favorites

  

Alert Print | Reply | Quote | Top

kocho Basic MemberMon 04-Dec-06 06:39 AM
1756 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#11. "RE: D80 Backfocus UPDATE"
In response to Reply # 0


Metro DC, US
          

Rather than repeat, here is the link to my post on the subject at DPReview:

http://forums.dpreview.com/forums/read.asp?forum=1034&message=21129453

The main question I have is, why did three out of three D80 bodies have some backfocus (I think I have reasonably ensured it is not due to user error). Is this something Nikon would do on purpose or just poor QC, or did I very consistently screw-up my countless tests every time?

My PBase Gallery Favorites

  

Alert Print | Reply | Quote | Top

    
Len Shepherd Gold Member Nikonian since 09th Mar 2003Tue 05-Dec-06 08:53 PM
12722 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#12. "RE: D80 Backfocus UPDATE"
In response to Reply # 11


Yorkshire, UK
          

Looking at the "real world" results in reply 8 none of the 3 pictures are likely to AF reliably according to Nikon's guidance on page 59 of the D200 instruction. My conclusion based on these examples of unreliable AF test targets homes in on
> or did I very
>consistently screw-up my countless tests every time?
Sorry - on the evidence of these tests you probably did screw up the testing

Photography is a bit like archery. A technically better camera, lens or arrow may not hit the target as often as it could if the photographer or archer does not practice enough.

Len Shepherd

  

Alert Print | Reply | Quote | Top

        
kocho Basic MemberWed 16-Jan-08 02:11 PM
1756 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#16. "Len,"
In response to Reply # 12


Metro DC, US
          

>Looking at the "real world" results in reply 8 none of the 3
>pictures are likely to AF reliably according to Nikon's
>guidance on page 59 of the D200 instruction. My conclusion
>based on these examples of unreliable AF test targets homes
>in on
>> or did I very
>>consistently screw-up my countless tests every time?
>Sorry - on the evidence of these tests you probably did
>screw up the testing

Len,

The "real world" shots were an illustration that most of the time I am able to get the focus where I want it after the adjustment. I would never trust these for a definitive evaluation of correct autofocus.

I would still disagree that the "tomato and scotch tape" test is bad - the tape box is a high contrast parallel target of sufficient size with nothing around it to confuse autofocus. The tomato handles just show how the DOF is about evenly distributed inforont and back (left tomato is slightly forward of the tape box and the right is slightly behind it).

For focus tests, I used the target shown below and moved the camera back till I got the best sharpness. After adjustment I was able to get the best sharpness straight out from autofocus. This target is mounted so it swivels to a 45 degree position after I focus in the parallel position. This way I can also observe the amount of autofocus in a more "lazy" manner without moving the camera back if I chose to do so.

The above mentioned shots were taken just to confirm that autofocus works on stuff that looks like what I might be shooting normally, rather than a flat target.

Finally, I recently got a Tamron and a Sigma lens to evaluate (f/2 versions). Both had consistent front focus relative to the 18-135 lens on the same body, using the same targets. My results are repeatable in both the front and backfocus on the same targets as long as I use different lenses on the same body and the same settings otherwise. So this is a good indication that my testing methodology is sound - if it were skewed, I would be getting either inconsistent or all backfocus results... In fact it is pretty sensitive as it distingwuishes the small amount of front/backfocus b/w the three lenses pretty clearly: the 18-135 focuses most towards the back, the Sigma is in the middle, the Tamron - most on the front. My 180mm AFD is yet a little further to the front, but that lens is defective and awaiting service for this problem.

Regards,
Mihail

My PBase Gallery Favorites

Attachment #1, (jpg file)
Attachment #2, (jpg file)

  

Alert Print | Reply | Quote | Top

            
Len Shepherd Gold Member Nikonian since 09th Mar 2003Thu 07-Dec-06 10:57 PM
12722 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#13. "RE: Len does listen"
In response to Reply # 16


Yorkshire, UK
          

- and notes the 2 test targets in your last post (due to very fine and limited detail at the centre of the frame) are ones where all recent DSLR body instructions and wide angle DX lenses say AF may not work well.
As you have ignored Nikon's advice on selecting reliable AF targets I remain 100% unconvinced. Send me similar results based on a good AF target and I will happily acknowledge yours is the first of 109 similar claims I have seen in the last 6 months supported to testing with good AF targets.

Digressing - dof of field varies from equal both sides of the point of focus in close up to infinitely more behind the focus point depending on subject magnification, viewing conditions, aperture, and to a lesser extent focal length. Where depth of field falls is not itself an indicator of front or back focus.

Photography is a bit like archery. A technically better camera, lens or arrow may not hit the target as often as it could if the photographer or archer does not practice enough.

Len Shepherd

  

Alert Print | Reply | Quote | Top

                
kocho Basic MemberThu 07-Dec-06 11:35 PM
1756 posts Share on Facebook Share on Twitter Share on Linkedin    Click to send email to this author Click to send private message to this authorClick to view this author's profile
#14. "RE: Glad to hear it :)"
In response to Reply # 13


Metro DC, US
          

>Len does listen - and notes the 2 test targets in your last post (due to
>very fine and limited detail at the centre of the frame) are
>ones where all recent DSLR body instructions and wide angle
>DX lenses say AF may not work well.

How fine is fine enough to confuse the sensor? Remember, this is a full-frame photo of the target, not a center crop. It is pretty big in the viewfinder and you can't find a place in it where focus hunts at any autofocus setting and any sensor.

There are four large circles and the inside semi-circles on the right are pretty fat. Remember that this is a parallel target, not a slanted test, so as long as there are enough wide and contrasty areas to lock focus reliably, it should work.

I hate to refer to authority as they are often wrong, but I'll do it anyway . This is an enlarged central portion of a standard resolution chart so it is designed to focus well on. It has detail on the diagonal direction and it is not straight lines only. The "fine detail" I put in to help with quickly evaluating DOF position - as far as I understand how focus works, this is only icing on the cake for the sensor, as the lines are fatter than 1 pixel and exceed the resolution of the camera/lens. The four circles are fuzzy and pixelated on purpose, the rest of the target has sharp edges.

With the center censor on wide setting there is plenty of large detail IMO.

The consistency of my results is what counts however. Whether this target resembles what Nikon states is a poor target is very questionable IMO - it might if it were shot from 10 feet at 17mm. It does not if shot from 4 feet at 50mm.

Just today, I had a chance to test another new used lens I just got for travel (Sigma 70-300 APO DG) and it happens to focus in the same way the 18-135 and the 50mm do, while the Tamron and the Sigma front-focus slightly, the Tamron a little more than the Sigma.

>As you have ignored Nikon's advice on selecting reliable AF
>targets I remain 100% unconvinced. Send me similar results
>based on a good AF target and I will happily acknowledge
>yours is the first of 109 similar claims I have seen in the
>last 6 months supported to testing with good AF targets.
>
OK. What should be the size of the target, the shape of the target, the distance from the target and the focal length of the lens so that it fits your definition of a "good" target? I'll happily snap a shot to see if I'm still on-target

>Digressing - dof of field varies from equal both sides of
>the point of focus in close up to infinitely more behind the
>focus point depending on subject magnification, viewing
>conditions, aperture, and to a lesser extent focal length.
>Where depth of field falls is not itself an indicator of
>front or back focus.
True. At near the minimum focus distance DOF should be more or less equally distributed front/back and the rear portion grows relative to the front portion as distance from the target increases.

My PBase Gallery Favorites

  

Alert Print | Reply | Quote | Top

Forums Lobby GET TO KNOW YOUR CAMERA & MASTER IT Nikon D90/D80/D70 (Public) topic #6258 Previous topic | Next topic