Does AF problem depend on lenses?

Started Jul 22, 2012 | Discussions
Paul Liukas
Paul Liukas Regular Member • Posts: 362
Does AF problem depend on lenses?

I've been tuning AF on my d800 and testing left AF problem as discussed everywhere.

Made AF tuning identical as LV on all my prime lenses (will write later, how I made it identical, accidentally). Center, left and right focus points where tuned perfectly on:

50 1.8G
60 2.8ED
85 1.8G

but on 28 1.8G - center and right points perfectly tuned as seen on LV, BUT left is OOF.

Anybody knows? Can I assume my d800 has AF problem as 3 lenses have identical focus as LV and one lens has OOF on left point.

The distance to test object was approximately the same on all lenses.

Can it be d800 or 28 1.8G lens?

Thanks for your opinions.

P.

michaeladawson Forum Pro • Posts: 11,784
Re: Does AF problem depend on lenses?

The common wisdom out there seems to be that the problem shows itself best with wide aperture, wide angle lenses. The wide aperture piece makes a lot of sense if you really want to eliminate DOF from the equation as much as possible.

However, I'm not so sure you necessarily need wide angle. I was using a 60mm f/2.8D lens yesterday with my D4 and D800. Left and right AF problems were very easy to see. Same with my 50mm f/1.8D

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Mike Dawson

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Paul Liukas
OP Paul Liukas Regular Member • Posts: 362
Re: Does AF problem depend on lenses?

if you see left and right problems maybe here is AF tune problem? that's very strange, you have problems with 50 and 60 lenses, i don't, but have with 28. Is that the answer that these AF problems differ?

michaeladawson wrote:

The common wisdom out there seems to be that the problem shows itself best with wide aperture, wide angle lenses. The wide aperture piece makes a lot of sense if you really want to eliminate DOF from the equation as much as possible.

However, I'm not so sure you necessarily need wide angle. I was using a 60mm f/2.8D lens yesterday with my D4 and D800. Left and right AF problems were very easy to see. Same with my 50mm f/1.8D

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Mike Dawson

michaeladawson Forum Pro • Posts: 11,784
Re: Does AF problem depend on lenses?

Trust me, I don't have an AF Fine Tune problem. I have already fine tuned all my lenses using Reikan FoCal. The center AF point focuses spot on with Live View matching the normal VF focus perfectly. I just happen to have left and right AF points that are both off. Live View focus on the left and right is perfect and matches the center point. VF focus using left and right points is way off, backfocus is about 3 inches.

It is entirely possible that there are different types of AF problems out there. I haven't tried my 70-200, 17-35, 28-70, or 24-120 lenses yet. I suspect that they will show the same issue as my 50 and 60mm, but who knows.

Paul Liukas wrote:

if you see left and right problems maybe here is AF tune problem? that's very strange, you have problems with 50 and 60 lenses, i don't, but have with 28. Is that the answer that these AF problems differ?

michaeladawson wrote:

The common wisdom out there seems to be that the problem shows itself best with wide aperture, wide angle lenses. The wide aperture piece makes a lot of sense if you really want to eliminate DOF from the equation as much as possible.

However, I'm not so sure you necessarily need wide angle. I was using a 60mm f/2.8D lens yesterday with my D4 and D800. Left and right AF problems were very easy to see. Same with my 50mm f/1.8D

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Mike Dawson

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Mike Dawson

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WGHalvorsen
WGHalvorsen Regular Member • Posts: 471
Re: Does AF problem depend on lenses?

May I ask, what is the difference between the AFFT values for the center and left focus points you get with Reican Focal for the 50mm f/1.8D?

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michaeladawson Forum Pro • Posts: 11,784
Re: Does AF problem depend on lenses?

In fact, the AFFT runs out of room at -20 on the left AF point on my D800. In other words, it's at -20 and still needs more. Part of the problem with my D800 is that I already have my AFFT set to -13 just get the center point properly tuned. Almost all my lenses need a -10 to -15 on the D800. My 70-200 is at -20 and still needs more.

Camera definitely has to go in for service. But I'm holding off for a bit until I have a little more confidence that El Segundo has the training and equipment to fix it the first time.

Mike

WGHalvorsen wrote:

May I ask, what is the difference between the AFFT values for the center and left focus points you get with Reican Focal for the 50mm f/1.8D?

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Mike Dawson

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Leonard Shepherd
Leonard Shepherd Forum Pro • Posts: 14,673
Re: Is it your AF target?

michaeladawson wrote:

Live View focus on the left and right is perfect and matches the center point. VF focus using left and right points is way off, backfocus is about 3 inches.

While Nikon do not mention phase detect outer AF points only read vertical detail on page 100 of the instructions, they do mention on page 47 LiveView may not perform well with vertical detail.

Central phase detect AF points read horizontal and vertical detail.

If your subject has poor vertical detail and good horizontal detail (camera in landscape position) you can get results like yours with any perfect LiveView body.

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Leonard Shepherd

Many problems turn out to be a lack of intimate knowledge of complex modern camera equipment.

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jean bernier Veteran Member • Posts: 3,177
Re: Does AF problem depend on lenses?

Normally, (I'm referring to "old" science) wide angles will give you largest Depth of field, but smallest Depth of focus.
Depth of focus refers to the depth behind the lens.

In other words, the position of the lens in regards to the sensor, or focus array, is most critical with wide angle lenses.

Worst case that can lead to OOF due to incorrect camera assembly, is :

wide angle
full aperture
short distance

and you could add: sensor size, as DX sensors are even more demanding. The smaller the camera, the more precision built is important. No wonder we used to focus LF by racking the lens litterally whole inches back in the days...

Now, if those old rules still apply to modern retrofocus design, I don't know. But a lot of complaints in these threads relate to wide angle...You might see a trend.
--
Jean Bernier

All photographs are only more or less credible illusions

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