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I am floored!!! I actually do have backfocus!!! (Large test pic)

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snriley

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I was one of those who have been laughing and joking about the so called backfocus issues.

Well, I guess what comes around goes around. When I got home I tested my D70 using http://www.photo.net/learn/focustest/ and it turns out that I have backfocus!!!

Here is my test:



I don't know what to do - I bought my camera from B&H back in the middle/end of March - so it has been more than two weeks. And they don't have any anyways. What should I do???

Help,
Steve

P.S. Sorry to those that I ever doubted, really sorry...
 
an angled subject which AF systems have trouble with...try to use a focus target that is flat and parallel and with high contrast vertical and horizontal features. I'll try to find the URL, but in the article I read, they stated that you'll think you have back focus if you use an angled subject to focus upon.

I think this is an important point! The two positions are very different and one is likely to be the way to go. Phil uses the parallel subject method FWIW.

AX
 
Well, please find that article for me because I really haven't thought any of my photos were very sharp - not like ones I have seen posted on this site.

Then I test and bam - I have backfocus...

Please find that URL!!!

Thanks,
Steve
msport said:
an angled subject which AF systems have trouble with...try to use a
focus target that is flat and parallel and with high contrast
vertical and horizontal features. I'll try to find the URL, but in
the article I read, they stated that you'll think you have back
focus if you use an angled subject to focus upon.

I think this is an important point! The two positions are very
different and one is likely to be the way to go. Phil uses the
parallel subject method FWIW.

AX
Click to expand...
 
Here's an example showing the camera aimed at a subject that is parallel. And with a ruler in the scene to act as the reference and not ALSO as the subject. Apparently that matters per some.



AX
 
Tripod? Cable release or from computer, tethered? Lens? Focusing distance? Angle to the target?and... try focusing manually.
--
no text
 
for that URL and will post if/when I find it. In the mean time, I have posted an example of a slightly different test method. (below) In this case, the camera/lens is AFed onto a subject with good contrast and at a certain distance and in parallel. An angled ruler THAT IS NOT FOCUSSED UPON is also in the scene so that you can gage the focus position. In a perfect world I think you're supposed to wind up with about 1/3 DOF in frot and 2/3 behind the subject.

You see, when you focus on something that is on an angle and use a AF sensor that has a size to it, some of the sensor sees the subject close and some further at the same time. In the real world if you run into this a manual focus or and AF and recompose might make sense.

AF is not perfect. Even different colors seem to affect it.

AX
 
msport said:
In a perfect world I think you're
supposed to wind up with about 1/3 DOF in frot and 2/3 behind the
subject.
Click to expand...
Not for short focusing distances.
msport said:
You see, when you focus on something that is on an angle and use a
AF sensor that has a size to it, some of the sensor sees the
subject close and some further at the same time.
Click to expand...
Right, IMHO.

--
no text
 
Hi Iliah, can you believe this?

Tripod. Timer. Kit lens.

70mm. Not sure about distance, maybe 10-12 inches. 45 degrees. Manual focusing the same result.

HELP!
Iliah Borg said:
Tripod? Cable release or from computer, tethered? Lens? Focusing
distance? Angle to the target?and... try focusing manually.
--
no text
Click to expand...
 
Ok, so I was wrong - I didn't measure it - maybe it was 15 inches.

I just kept moving slowly backward from the sheet til the camera said it was focused, planted the tripod, then refocused and shot with timer.

Argh!
msport said:
Hmmm!

AX
Click to expand...
 
Steve said:
What is that supposed to mean???
Click to expand...
Sorry, but I do not understand your question. I think I've said what I said :)
snriley said:
snriley said:
So, what? sensor has some size, and it is positioned not exaxtly
where you see the mark in viewfinder.
Click to expand...
Click to expand...
Testing should be done at approx. 8 feet from the target, and something contrasty (black cross on white paper) should be mounted to the ruler, so that focusing plane would be perpendicular to the lens axis. Lens zoomed to 50mm, good light 1/60 @ 5.6 for 200 ISO
--
no text
 
I think you're on to the reason that people think their unit has a definite back focus problem and then it checks out fine at the service center.

Gizmo
msport said:
Here's an example showing the camera aimed at a subject that is
parallel. And with a ruler in the scene to act as the reference
and not ALSO as the subject. Apparently that matters per some.



AX
Click to expand...
 
I'm not sure what Nikon means by minimum focus distance in terms of DOF at that point. If it means what it sounds like, things closer than that distance will not be in sharp focus and things past it can be. This may tend to increase the perception of back focus.

Since you did not measure, and since your distance was so close to the absolute minimum, why not try a test with a parallel subject and from some reasonable amount greater than the absolute minimum distance?

You can see an example of a parallel test in the URL I recently posted, or in Phil's D70 test or another one with a series of dice in the Canon 10D review on this site. All three of those use a subject that is parallel to the camera/lens under test.

AX
 
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