AF Issue + Free test pattern

Started Apr 7, 2012 | Discussions
D800Fanboy
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AF Issue + Free test pattern
Apr 7, 2012

I created a High Quality test pattern i am will to share it with anyone who wants it. I just need someone to show me how to upload the pdf file.

I did some tests with a 50mm lens at f1.4 for the AF issue. Can someone please look at them and tell me if they are ok. I did the test with the D800 and D300. Please look at my pics and give advice i still have 3 weeks to replace it if i need to. I may have shot the D800 slightly out of focus.

Nikon D300 Nikon D800
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gonzalu
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D300 still looks to be the same
In reply to D800Fanboy, Apr 7, 2012

difference in sharpness from left to center

MAKE SURE your image is aligned with the sensor... it must be perfect or else you risk an improper test.

Measure with a precise measuring tape, preferably a soft type, not a metal one, from the edges of the lens bayonet to the edges of your test pattern/wall... this will give you a reasonable degree of accuracy...

I would do it on a tripod and face the camera at the floor. Put your target on the floor and check the level of the floor then using a spirit level also check the level of the lcd screen on the back of the camera as it faces the target to get a reasonable degree of accurate alignment.
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Marcin 3M
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This test is not ...
In reply to D800Fanboy, Apr 7, 2012

showing the possibility of AF troubles (if I understand what's the nature of the problem).

You should shot Your test chart using different AF points and then compare results.
Regards.
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D800Fanboy
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Re: This test is not ...
In reply to Marcin 3M, Apr 7, 2012

Thanks guys, What i did was setup my tripod with the camera. Made sure the camera lens was level with the target and height was at center of target. Focused on the center of target. I also moved the camera in to fill the test pattern. I tried different AF points and they look fine but the 1.4 seemed to me just a little soft on the left

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samjstern
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Hey D800Fanboy, ...
In reply to D800Fanboy, Apr 7, 2012

did you try to calibrate the 50mm lens to the D800 and then shoot the test pattern??

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D800Fanboy
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Re: Hey D800Fanboy, ...
In reply to samjstern, Apr 7, 2012

No i did not, i'm learning a lot already. Looks like i'm gonna have to redo the test.
Is their a tutorial some were i can goto to learn how to calibrate the lens.

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Marcin 3M
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Re: Hey D800Fanboy, ...
In reply to D800Fanboy, Apr 7, 2012

You have to note, that lens may have some alignment imperfections, and may perform different on the left and right side. But this can be proven with a single shot of a subject paralel to the sensor's plane. Unfrtunatelly, it's quite oftenly observed flaw.

But we are talking about specific af system flaw. Isolating the problem may be really dificult if the lens is not perfect. Therefore try to use different lenses.
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GMack
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Re: AF Issue + Free test pattern
In reply to D800Fanboy, Apr 7, 2012

How about making one and trying to align the right and left high contrast targets with the one in the camera? Idea would be to move the internal focus point to either the right of left without moving the camera to see if their is a Right to Left focus error that may be an issue if you follow the D800 focus error thread.

Nikon seems to like the focus target below as it is the one in their lens repair manual.

Aside, is there a reason why the black circular pie target in the center isn't fully black but rather spotted? The photo maybe vs. the PDF?

Mack

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Event_shooter
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Here's a good chart for download
In reply to GMack, Apr 7, 2012
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Leonard Shepherd
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Re: AF Issue + Free test pattern
In reply to GMack, Apr 7, 2012

GMack wrote:

Nikon seems to like the focus target below as it is the one in their lens repair manual.

It can be a good target - but I expect Nikon have very specific guidance for viewfinder alignment.

Without very specific viewfinder alignment and focus distance relevant to focal length the camera AF could assume the center of the target is not where Nikon intend, leading to a possible front or back focus indication the lens does not have.

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Leonard Shepherd

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Leonard Shepherd
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Re: AF Issue + Free test pattern
In reply to D800Fanboy, Apr 7, 2012

D800Fanboy wrote:

I created a High Quality test pattern

The target is capable of providing a lot of information - with a however

The however is the AF target at the centre does not seem to meet Nikon's standard for consistent reliable AF in camera instruction books or at
https://nikoneurope-en.custhelp.com/app/answers/detail/a_id/4585

While AF often works very well with less than ideal targets sometimes a poor target can result in poor focus - indicating a fault with the target rather than the lens being tested

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Leonard Shepherd

Photography could be easier - if cameras and lenses came with an increase in skill button.

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Leonard Shepherd
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Re: Here's a good chart for download
In reply to Event_shooter, Apr 7, 2012

What convinces you it is a good target for testing AF?

It does not meet Nikon's guidance for consistent reliable AF in your camera instruction book or at
https://nikoneurope-en.custhelp.com/app/answers/detail/a_id/4585

While AF often works well with less than an ideal target sometimes a less than ideal target indicates a "focus error" which is a fault with the target rather than the lens.
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Leonard Shepherd

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DvD5
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Re: AF Issue + Free test pattern
In reply to D800Fanboy, Apr 7, 2012

You need to make sure your sensor is perfectly parallel to (and centered on) the target. You can do this a number of ways including measuring distance from floor for height, then measuring diagonals for right/left alignment. You can also have someone hold a mirror perfectly flat on the target and make sure you see the image of your lens perfectly in the center of your viewfinder.

I've noticed that I need to dial in negative focus adjustment for nearly all my lenses, so that may be part of the issue. Edges of the chart won't look all that great at f/1.4, but they should be similar sharpness to each other.

Don
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Leonard Shepherd
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Re: AF Issue + Free test pattern
In reply to DvD5, Apr 7, 2012

DvD5 wrote:

I've noticed that I need to dial in negative focus adjustment for nearly all my lenses, so that may be part of the issue.

If you are using a reliable AF target the likely problem is your camera body is out of AF alignment.

If you are not using a reliable target and always start focus from either in front or behind the target it could be your camera and lenses are OK.
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SteveL54
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Re: AF Issue + Free test pattern
In reply to Leonard Shepherd, Apr 7, 2012

Leonard Shepherd wrote:

GMack wrote:

Nikon seems to like the focus target below as it is the one in their lens repair manual.

It can be a good target - but I expect Nikon have very specific guidance for viewfinder alignment.

It is a good target.

The service manual does have a procedure to ensure the mirrors are properly aligned and flat. But this is not relevant to the suitablility of any chart or pattern as an appropriate AF target

Without very specific viewfinder alignment and focus distance relevant to focal length the camera AF could assume the center of the target is not where Nikon intend, leading to a possible front or back focus indication the lens does not have.

There is no sensitivity to the "center of the target". The entire target is parallel to the sensor, so the test is not sensitive to aim as you seem to think.

Last year Marianne and I (plus others) tried to explain to you how PDAF works.

http://forums.dpreview.com/forums/read.asp?forum=1030&message=37475367

If a camera/lens combination miss focuses when that target is mounted reasonably parallel to the camera either the camera or the lens (maybe both) need adjustment. It won't cause a false positive as you imply.

Steve

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Leonard Shepherd

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TOF guy
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Re: AF Issue + Free test pattern
In reply to Leonard Shepherd, Apr 8, 2012

Leonard wrote:

The however is the AF target at the centre does not seem to meet Nikon's standard for consistent reliable AF in camera instruction books or at
https://nikoneurope-en.custhelp.com/app/answers/detail/a_id/4585

That is not true. The target is perfectly adequate and meets Nikon's standard

While AF often works very well with less than ideal targets sometimes a poor target can result in poor focus

Can't be the explanation.

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lanef
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Re: D800Fanboy
In reply to D800Fanboy, Apr 8, 2012

Hi D800Fanboy, thanks for sharing, I would like to give your chart a try, would you mind email me a PDF? Thanks

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Flashlight
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Some points on AF testing
In reply to D800Fanboy, Apr 8, 2012

On the local forum someone had a D7000 with focus issues, brought it to Nikon that simply made a +10 adjustment for his 50mm lens. He still had issues. The guy asked for help and I spent some time helping him out. He made the shots on my instructions, uploaded the NEFs and I did the processing. Something interesting was shown:

First I had him make a 45 degree triangle cardboard test target with letters on the front, put it on a piece of paper with lines and set the camera @ 45 degrees. The letters were a bit larger than I intended so he focused on the edge of the round part of the '5'. Also, the camera was slightly off-axis. Focus distance is 2 meters, all test shots taken with AF-S:

I ran the shots through a Photoshop action, involving 'Find Edges' and contrast manipulation. This is a shot with Live View Contrast AF:

First off the lens seemed misaligned, although part of this could have come from the camera placement. The purple line indicates the focal plane as seen on the full sized image:

Then I had him make series of 5 shots each. The first series is where he moved the plane of focus closest to the camera before each shot, then focus once and take the shot (leftmost is control shot with Contrast AF):

Then I had him turn the focal plane closest to the camera before each shot like in the first test, but now half-press the shutter button 5 times so the focus had time to 'settle' and take the shot (leftmost is control shot with Contrast AF):

As you can see when you compare the first and second series, repeatedly half-pressing the shutter button and focusing before each shot makes the D7000 focus much more consistently. It was also proved that the +10 AF Fine Tune setting made by Nikon was not optimal and should probably be +5 or 0.

I would also not use the AF-C + AF-ON focus method with this camera, as repeatedly focusing on the same target has no effect when using AF-C.

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Philip

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Photo Pete
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Re: Some points on AF testing
In reply to Flashlight, Apr 8, 2012

And how was the focus accuracy at 50m distance and f4? I'll bet a different fine tune setting would be required!
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Flashlight
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Re: Some points on AF testing
In reply to Photo Pete, Apr 8, 2012

Photo Pete wrote:

And how was the focus accuracy at 50m distance and f4? I'll bet a different fine tune setting would be required!

That usually happens with miscalibrated lenses. As far as the experiment above goes, I was already happy to convince the tester not using the closest possible focus distance but a 'whopping' 2 meters. Personally I always test lenses at several focus distances.

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Philip

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