D800 and SB-910 backfocused images with flash AF assist

form

The issue is this, which has apparently been a very long-standing issue I myself have only recently experienced for the first time since buying a Nikon flash: When the SB-910 (in my case) flash AF assist is enabled AND the flash AF assist lamp fires, my Nikon D800 camera will ALWAYS focus inaccurately or push the focal plane at least -15 microadjustment points back versus when the flash AF assist lamp does not fire. Since the AF assist lamp only activates in AF-S mode, the issue only occurs in AF-S mode.

In my case, my 35mm f/1.4g focuses accurately with NO AF assist lamp, or using the camera's built-in AF assist lamp, using about -5 microadjust. If my SB-910 is mounted, turned on, and the flash's AF assist lamp activates, -5 microadjust ALWAYS results in severely back-focused images. When the flash's AF assist lamp activates and I have the camera set to -20 microadjust for the 35mm f/1.4g, then focus is ALWAYS accurate (as long as the target is lockable). Several people have tested the results when covering the AF assist lamp, and the result is roughly the same as when the AF assist lamp is not covered.

Reports of this issue with previous cameras and flashes have existed since long before the D800 and SB-910 were announced. However, the most glaring and frequent reports involve the D800. The issue apparently is not experienced to the same degree by all persons, and a few have reported not having the issue at all.

The only solution ever suggested has been to turn off flash AF assist, which is not a real solution because it does not provide the advantageous flash AF assist lamp that is half (or more) of the reason to have an on-camera flash in low lighting. The built-in camera lamp is both intrusive to subjects and not very effective at even moderate distances, and the camera often will not be able to lock accurately without any focus assist. This is a workaround, not a solution. There needs to be a solution.

Some persons have reported not having this issue with the SB800 or with different cameras (sometimes different model, sometimes same model) in combination. However, some have reported the issue with SB800 as well.

I have posted on another forum a compilation of the links I have found related to this issue so far. This is the first day the list has been up, and it continues to grow.

Please keep this topic alive. This is a long-standing, widespread (though not universal) issue people have been encountering for years with at least two generations of Nikon cameras and flashes. Not everyone has the issue with the same combination, but those who do have the issue need to share it with the outside world. I am making a point to expose this as the larger scale issue it truly is. We deserve to have the flash focus assist lamp work properly and not cause a new problem. Nikon needs to resolve this problem by correcting it, not trying to hide it under the rug. They never publicly acknowledged the widely-reported D800 left-side AF issue that many users (including myself) had, and they only acknowledged the D600 oil spots issue immediately after a class-action lawsuit was announced and China had publicly denounced the Nikon D600 camera issues. What will it take for them to do the right thing?

A company with a repeating show of unethical behavior demonstrated by all of these recent issues that they ignore and/or deny the existence of (until a major country denounces them) will very likely develop a negative stigma over time. That stigma could do far more damage than the price of some additional effort to acknowledge and resolve issues and keep the highest reasonable percentage of satisfied customers possible.

I am a long-time Canon user who has grown frustrated with some flaws and deficiencies in recent Canon products and have started trying out Nikon products because of that. I want Nikon to be a viable competitor and alternative, but issues like this make it extremely difficult.

sevencrossing

I have been using an D800 since it came out and a D700 before that with an SB 900. never noticed a problem

A company with a repeating show of unethical behavior demonstrated by all of these recent issues that they ignore and/or deny the existence of (until a major country denounces them) will very likely develop a negative stigma over time. That stigma could do far more damage than the price of some additional effort to acknowledge and resolve issues and keep the highest reasonable percentage of satisfied customers possible. - ????????????

form

Every time they deny/ignore an issue like the D600 sensor oil spots or the D800 left side AF back focus, it's poor handling of a real problem with their products. It literally took a class-action lawsuit against Nikon for the D600 sensor oil spots to get them to acknowledge the sensor oil issue.

http://www.dpreview.com/news/2014/02/26/nikon-to-offer-d600-shutter-replacement-to-address-dust-issue?utm_campaign=internal-link&utm_source=news-list&utm_medium=text&ref=title_0_10

Within a few days of the class-action lawsuit regarding D600 oil spots going public - http://nikonrumors.com/2014/02/24/law-firm-already-filed-a-class-action-lawsuit-for-the-nikon-d600-dustoil-spot-issue.aspx/

It's not a coincidence. It's what it took to get them to acknowledge a real, functionally-limiting issue.

This issue with the flashes is absolutely real, functionally limiting, and quite a number of people have experienced it even though others have not. The same applied to the D800 left AF point backfocus issue. It is real, functionally limiting, and a number of people experienced it personally (including myself). Nikon has still not acknowledged it publicly.

I have myself found the Canon 5d3 to focus slower and front focus more often in lighting situations where the 5d2 focuses faster and needs no AF assist to do so. I've even sent the 5d3 in to Canon and got a bill and an insulting response from them. However, my 5d3 experience is far more isolated and subjective than the vast majority of pro-Canon persons, so that topic has no impetus whatsoever. This one may have some thrust, and it should, because it's a very significant problem. I literally cannot use my flash AF assist on my D800 to do the things the AF assist is meant to do unless I want to manually adjust the AF microadjustment every time I target something that doesn't need AF assist or when I go into AF-C mode.

sevencrossing

I going to guess you have taken your D800 back to the retailer/ supplier
What was there reaction?
I am a bit puzzled by your AF -C comments the flash AF assist only works on AF _S

form

Exactly, it doesn't happen in AF-C mode because the focus assist doesn't come on. I said that exactly. In AF-S, some things are illuminated enough so as not to cause the flash AF assist to fire, and in those cases the behavior is exactly as if there was no flash mounted - it focuses as if -5 microadjust was the correct setting. The same as if the camera is in AF-C mode. The only time the issue occurs is in AF-S mode when the flash AF assist fires. The problem is, I need it to fire when it needs to and not when it doesn't, and I need to have it focus without any microadjustment tweaks between images because I am using this camera for work. If I was not using it for work, the issue would be a nuisance but not as critical. However, as a work camera the issue is critical.

I got my D800 from Lensauthority a while back and have been overall satisfied with its function. The addition of an SB-910 was the first real major issue I've had with the camera.

Ironheart

Why not rent another D800 and SB910 and do some swapping to determine if it is the camera, or the flash, or both. If you can narrow it down, send whichever part is offending off to Nikon for repair. Or send both with a problem description and photos. It may be a simple adjustment.

Vipmediastar_JZ

@form I remember reading on that and also using the sc-29 sync cable.
I know I tested mine in nov 2013 with the sb-910 but I do not remember the results. I can certainly re-test with the d800 and DF using the sync cord and with out it and also trigger them with the phottix odin to see if i have an issue and if it only happens with the d800. It may take a while since I don't have my d800 back from repair for FOCUS issues

TaoTeJared

Sorry bud but if there is a difference, it is 100% user error. It is either your release settings or a different way you shoot or something you have done - not the flash or the camera.
Having the SB-910 or any other flash with flash AF assist Has ZERO effect on "moving" any focal/focused point. NOTHING CHANGES WITH FOCUS OR ANYTHING, WITH IT MOUNTED.

It projects lines onto the subject, and the AF sensor now has lines to "grab" the focus instead of trying to find "definition" on the subject alone. It is an unconnected item that only knows to turn on or turn off. The camera itself doesn't change anything either. All that has been added is a light source to lock focus onto. You can do the same thing by using a projector to project lines onto a subject. There is no difference. If there was, you would see huge issues with all the 3rd party flashes that use the same type of system as well - and you don't.

Reset your camera and reset your flash. And if you still think there is something, turn the AF assist off on the flash.

spraynpray

@TaoTeJared: It could be this is one of those non-obvious things (like your interpretation of the focusing when using P mode that caused so much interaction because it was illogical/counter-intuitive). Do you have an SB-910 to try it with?

@form: does your body do it with the SB-900? Do you know anybody with an SB900/910 and D800 that doesn't experience it? Can you try their components?

sevencrossing

spraynpray as TaoTeJared says it does not matter which flash you use, they just project a light

form
Can you give us some more information
what subject are you shooting?
what are the lighting conditions?

spraynpray

Sorry sevencrossing, I did not realise you were a fully qualified and currently employed engineer working at Nikon on the DSLR bodies. As it seems you are, perhaps you could answer the questions raised here like the cause of D600 sensor contamination etc. )

Given that the camera knows when a flash is connected, who knows what communications could be taking place and what bugs there could be in the firmware causing whatever effects. I don't, and I was a qualified electronics engineer before I retired. Give me a set of schematics and specs, and I could get closer to possibly knowing.

sevencrossing

No S&P I don't work for Nikon
but the only connect between the flash and the camera is the Hot shoe
http://static.photo.net/attachments/bboard/00S/00SHyc-107585784.jpg
there does not seem to a contact for focus information

Focus assist only comes on, in low light, so my guess is forms issue may be caused by spurious lights
I sometimes get problems with "disco lighting " in dance floors

PB_PM

spraynpray as TaoTeJared says it does not matter which flash you use, they just project a light

form
Can you give us some more information
what subject are you shooting?
what are the lighting conditions?

Don't be so sure about that. If I recall correctly Nikon already issued a fix for the D4 in a firmware update to deal with this very issue.

sevencrossing

there does not seem to a contact for focus information

I could be wrong at lot data is transmitted between the camera an the flash
The flash "knows" what focal length of the lens
The camera "knows" if you have added a gel to the flash

http://cms.diodenring.de/electronic/microcontroller/110-ittlanalysis#hardware

spraynpray

Now you're starting to see... Think CAN bus - multiple functions carried on one conductor.

sevencrossing

They clearly can S&P
but AF is done by the camera looking through the lens
For the flash to give the camera incorrect focus information, the flash would have to have a lens
as it does not have a range finder or know how far the subject is away
The flashgun assists the camera to focus, by simply shining an IR beam on the subject and the camera does the rest
one I think AF assist only works with matrix/ grid focusing, not spot
so I am too sure, how it possible to define exactly how far the focus is out

TaoTeJared

My guess is that @form has one of the "auto" 51/11/9 AF points set up and it is grabbing a focus point other than what "object" he wants focused. Using AF-C 51 3D will grab multiple points. If you want the Eye, it does not know that and may grab the nose, shoulder and hair and average the focal point.
Other thing is using Release priority instead of Lock priority - that will. I'm actually wondering if adding the Flash could change one of those or rather the camera Remembers the setting. Or it may be as simple as Switching Modes the camera remembers. I'd have to check that - I keep my stuff on the same settings all the time so I would have to play with it.

To save some headaches - I think this (@Sevencrossing) Reads differently than what he Intended to say.

spraynpray as TaoTeJared says it does not matter which flash you use, they just project a light

form
Can you give us some more information
what subject are you shooting?
what are the lighting conditions?

I believe he agreed with the response and was asking @form to provide proof. Quite frankly I agree with that as I have never heard of any issue like this either.

@Sevencrossing - make sure to use the "@" when talking to people, this is what bolds the user.
"form" is a poor choice in a user name from an english speaking perspective.

spraynpray

They clearly can S&P
but AF is done by the camera looking through the lens
For the flash to give the camera incorrect focus information, the flash would have to have a lens
as it does not have a range finder or know how far the subject is away
The flashgun assists the camera to focus, by simply shining an IR beam on the subject and the camera does the rest
one I think AF assist only works with matrix/ grid focusing, not spot
so I am too sure, how it possible to define exactly how far the focus is out

Not if the focus error is due to a problem with the firmware - I believe it is possible that it is not easily predictable if that is the case.

Ade

Not if the focus error is due to a problem with the firmware - I believe it is possible that it is not easily predictable if that is the case.

That is the prevailing 'theory'... when the red/near-infrared flash AF Assist light comes on, the focus point needs to be shifted by a certain amount to compensate for the longer average wavelength. This is similar to the need to shift focus when doing infrared photography.

This compensation is applied in firmware but cannot take account of all possible variables (e.g., the % contribution of the Assist light vs. ambient light, effects from different lenses, etc.) So in many cases the compensation amount will be wrong, resulting in a focus miss.

With the D800/e, the high resolution sensor makes any focus miss more obvious than before, at least when evaluating images at 100% (since the focus blur is spread among more pixels). However in theory this issue will occur with any camera body, not just Nikon but also with Canon, etc.

Personally I've always turned off the AF Assist light so I've never rigorously tested possible scenarios.

clskelton

I tested my SB-700s and SB-910 on my D7100 and it focuses perfectly with the red AF assist. I used a 85mm 1.8G lens at f/1.8 from four feet away.

@form: if you perform the same tests with the red AF-assist panel covered up, do you get the same results?

lbaraldi

This is a issue with the focusing system. Can occur with any camera, but I have seen many complaints about the D800.

There are two solutions:
  - Turn off the focus assist the camera and the flash unit, or ...
  - Send the camera to Nikon, detailing the problem and request service for recalibration in the focus system.


"Made in Japan" is no longer synonymous with absolute quality!

Vipmediastar_JZ

Here is a minor update.
I received my D800 from re-repair Nikon said to check my lens so I did. While I was doing this with the 70-200mm the on camera AF light was on and I un-focused the lens in both directions on one end it struggled when the light was activated as the lens blocked it. I turned it off and it no longer struggled. Somehow the AF light made the camera dumb.

I couldn't do a thorough test as promised. I was testings focus issues with my D800 first and I'm done for the day.

Gareth

This is NOT user error!

I have experienced the same issue. I thought it was my yongnuo triggers at first, but it was actually the sb700 I was using as a master. Now there is a tx I don't need to have a flash on camera as a master, problem solved.

sevencrossing

I think it is important to remember AF "ASSIST" only kicks in, in low light conditions, when the camera is struggling to focus

If the camera fails to focus in difficult conditions, may be it not a user error
but, perhaps , the OP has come to rely on AF too much

Gareth

af assist kicks in, in my lounge at night with the lights on...

PB_PM

Most artificial light sources are weak, so that would be considered low light.