D800 + SB 900 AF Assist On = Back Focus Issue

Started Apr 7, 2012 | Discussions
D800 Regular Member • Posts: 199
D800 + SB 900 AF Assist On = Back Focus Issue

All,

Looks like both of my D800 bodies have back focus issue with SB 900 AFA on. I did not have this problem with my D700 body (with the same SB 900). AF works fine without SB 900, or SB 900 with AF off. AF also works fine with AF on from SB 900 in LV or in AF-C mode. Please refer to below images for more info.

1. SB 900 flash off (AFA off), focus right in the middle of the bottle, minimum focus distance. No issue with focus

2. SB 900 flash on, AFA off, sharp at the focus point (middle)

3. SB 900 flash on, AFA on, focus in the middle of the bottle. Results in back focus

4. SB 900 flash on , AFA off, focus distance increased.

5. SB 900 flash on, AFA on. Back focus

Images 1-3 were taken at minimum focus distance. Images 4-5 taken with increased focus distance which looks worse. IMO, auto focus assist from SB 900 is unusable.

Please confirm this issue with your D800 and SB900 if you have time. Hopefully, only my bodies have this issue.

Thanks

Nikon D700 Nikon D800
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Leonard Shepherd
Leonard Shepherd Forum Pro • Posts: 14,562
Re: D800 + SB 900 AF Assist On = Back Focus Issue

Why not start with your camera instruction book or
https://nikoneurope-en.custhelp.com/app/answers/detail/a_id/4585

Assuming the camera is using flash focus assist the projected bars are likely to be at the center of the bottle curve, and further away at the edges of the bars.

Nikon confirm in example 3 in the link a target like the one you are using can cause poor focus.

If focus assist works good projected on a flat target parallel to the sensor the likely cause is less than perfect testing.
--
Leonard Shepherd

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

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gDaniel
gDaniel Regular Member • Posts: 167
Re: D800 + SB 900 AF Assist On = Back Focus Issue

i am experiencing same issue with SB-900. In the beginning i thought that my Sigma 85 f1.4 was the culprit but then i tested the other lenses as well ( 50 1.4 af-s, 35 af-s, etc) and all experience backfocus.

I cannot reproduce the error with SB-600 attached!

My D800 firmware is 1.000/1.000, Europe version.

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reginalddwight Senior Member • Posts: 2,003
Ditto

Thank you for bringing this to my attention. I had the on-board AF-assist in the flashguns turned off but when I turned it on, replicated your findings.

Same OOF images with my SB-900 and SB-700.

More bugs to iron out in the D800 in a forthcoming firmware update.

thomas2279f
thomas2279f Senior Member • Posts: 2,850
Re: Ditto

Thanks for sharing your findings.

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OP D800 Regular Member • Posts: 199
Re: D800 + SB 900 AF Assist On = Back Focus Issue

Leonard Shepherd wrote:

Why not start with your camera instruction book or
https://nikoneurope-en.custhelp.com/app/answers/detail/a_id/4585

Assuming the camera is using flash focus assist the projected bars are likely to be at the center of the bottle curve, and further away at the edges of the bars.

Nikon confirm in example 3 in the link a target like the one you are using can cause poor focus.

If focus assist works good projected on a flat target parallel to the sensor the likely cause is less than perfect testing.
--
Leonard Shepherd

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

This happens with single focus point, and center focus point is used.

In all example images, single and center focus point was used to focus at 2 letter "PO" of the word "Possible". I expect the same result as in image # 2 and 3.

Yes, I got back focus even with flat target parallel to the sensor. In fact, all of my images that taken with AF-assist on had back focus. I love to use the AF-assist illuminator to help getting near instant focus in low light situation. Without this it just takes longer to lock on. It worked fine with my D700, not just D800.

OP D800 Regular Member • Posts: 199
Re: Ditto

reginalddwight wrote:

Thank you for bringing this to my attention. I had the on-board AF-assist in the flashguns turned off but when I turned it on, replicated your findings.

Same OOF images with my SB-900 and SB-700.

More bugs to iron out in the D800 in a forthcoming firmware update.

Thank you for taking the time and confirm this issue. Looks like it is a bug with D800 and SB 900. I will report this bug to Nikon and hopefully we will have a fix soon.

Mykal Forum Member • Posts: 66
Re: D800 + SB 900 AF Assist On = Back Focus Issue

Just got my D800 and I am having this issue too. Back focus with sb700 and sb900 focus assist with all my lens. Dialing in -20 auto focus fine tune helps but photos are still sharper without focus assist.

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Mykal Forum Member • Posts: 66
Re: D800 + SB 900 AF Assist On = Back Focus Issue

Just tried with an sb800 and no issues.

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macphoto Regular Member • Posts: 204
Re: D800 + SB 900 AF Assist On = Back Focus Issue

I've long had the same problem with both of my D3s bodies and both D700 bodies as well. Happens with the SB900, but not with the SB600 (I don't have an SB800 to test), and also happened with the SB700 (which I returned after it displayed the same issue). It's most noticeable with primes and at longer focus distances.

-- hide signature --

Michael

WildSammy Senior Member • Posts: 1,069
Not only D800 problem!

I have the same issue with my D700 and all lenses I have.. I have SB-700 flash, but it was the same with SB-900 which I borrowed for test.

I think it's a software bug, but I don't know.. more users over internet are reporting this backfocus problem when AF assist on flash is enable.

No resolution yet

PS. It's only present with SB-900 or SB-700 flashes.. with SB-800 or SB-600 this issue isn't present.

It will be interesting to test it with SB-910.
--
S.

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OP D800 Regular Member • Posts: 199
Re: D800 + SB 900 AF Assist On = Back Focus Issue

FYI,

Looks like Nikon has fixed this issue (D800+SB900). At least the newest camera recently received from Amazon.

Mykal wrote:

Just got my D800 and I am having this issue too. Back focus with sb700 and sb900 focus assist with all my lens. Dialing in -20 auto focus fine tune helps but photos are still sharper without focus assist.

GMack Senior Member • Posts: 2,928
Re: D800 + SB 900 AF Assist On = Back Focus Issue

D800 wrote:
FYI,

Looks like Nikon has fixed this issue (D800+SB900). At least the newest camera recently received from Amazon.

Mykal wrote:

Just got my D800 and I am having this issue too. Back focus with sb700 and sb900 focus assist with all my lens. Dialing in -20 auto focus fine tune helps but photos are still sharper without focus assist.

Where is this fix info? I have a new D800E and just discovered this flash back-focusing assist-light thing (needing a -20 or more) with SB-900. Firmware for the flash is still the older 5.02 on their website since 4-2011.

Mack

BozillaNZ Regular Member • Posts: 346
Re: D800 + SB 900 AF Assist On = Back Focus Issue
1

There must be come physical reasons why this is happening, because my 1D3 + 580 EX II also exhibits the same issue! Focus Assist on = back focus. I have to dial in -10 in AFMA to get it back on track when AF assist is on. So it's not a Nikon only problem.

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jonstatt Regular Member • Posts: 418
Try focusing in a room with yellow walls!!

I have found the D800 to be terribly influenced by the colour of light in the room. This doesn't just apply to the difference between incandescent and natural light, but also the effective reflected lighting in a room with coloured walls. Once again, like the focus concerns, this seems to be affected more at wide angle fast lenses than others. I have noticed as much as 6-7 AF fine tuning point variation with a room with yellow walls (with daylight coming in through the window) vs a room with white walls.

I suspect that this variation is also responsible for the effect being described with AF assist lights.

I would have thought this was curable with a firmware update. I have tried two D800s (one with the AF problem and one without) and this specific colour of light behaviour is the very same for both. So it is not a hardware fault as such.

inasir1971
inasir1971 Veteran Member • Posts: 3,623
Not a 'fault' known issue

This issue was looked at some weeks ago and is known.

The short answer is unless you have a truly apochromatic lens this will happen. Refraction of light is dependent upon wavelength of light, hence the issue of LoCA's, and lateral CA - well all CA really. Red light (as in the AF assist illuminator) is at one extreme end of the visible spectrum and as such is a very bad idea to use for focus illumination.

Ideally, illumination for focus should be same as that for picture, failing which some light source that has a broad spectrum of light - e.g. a flashlight (not one of those blue LED things) and I am being entirely serious.

Here's a link to the thread discussing this:

http://forums.dpreview.com/forums/readflat.asp?forum=1021&message=41999733

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OP D800 Regular Member • Posts: 199
Re: Not a 'fault' known issue

Either latest firmware fixed this issue or Nikon fixed it in new D800 bodies!

2 recent D800s received from Amazon have extremely accurate AF with AF assist on.

GMack Senior Member • Posts: 2,928
Re: Not a 'fault' known issue

D800 wrote:

Either latest firmware fixed this issue or Nikon fixed it in new D800 bodies!

2 recent D800s received from Amazon have extremely accurate AF with AF assist on.

My D800E exhibits it still (needing something stronger than a -20, but my body seems to be around a -10 as it is, and some lenses are hitting the minus tuning adjustment wall too.). I opened a case with Nikon about it (Nikon in Barcelona, Spain responded?) and they closed it as "Resolved" a few hours later. Fantastic.

I believe it has to do with the color of the light as do others and why Nikon uses the "white" light on their bodies over the "red" light off their flash. They aren't about to say though or admit it. The SB-920 (or whatever) may end up being "white" too.

So I leave it switched Off and use a Surefire U2 LED torch if I have too as an assist light. Yeah, it blinds people as a side-effect if I don't dial it down even in daylight and accidentally hit their eye with its beam, but least it works.

Mack

nuno jorge Forum Member • Posts: 74
Re: D800 + SB 900 AF Assist On = Back Focus Issue

I have the same problem. but just with one lens Nikon 50mm 1.4G, and the flash is SB 910, I had two Nikon D800 bodies, and the same results on two bodies

Rikki Contributing Member • Posts: 509
Re: D800 + SB 900 AF Assist On = Back Focus Issue

Just came on to ask about this myself!

Nikon D700 + 24-70 f/2.8 + SB900 = Fine every single time with the SB900 red AF assist

Nikon D800 + 24-70 f/2.8 + SB900 = 80%+ miss rate. Thinks its locked but returns blurred images using SB900 and red AF assist.

That kinda tells me that my lens is fine and my flash is fine the only change being the D800 body.

Another thing to add to the list when I sent it back to Nikon UK I suppose

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