AF-C problems solved by AF Fine Tune or am I imagining things?

Started 7 months ago | Discussions
Robert Palmqvist
Regular MemberPosts: 447
Like?
AF-C problems solved by AF Fine Tune or am I imagining things?
7 months ago

I have been struggling with an AF problem for a while. I thought I should share some information if someone else is in the same position.

It all started with my first serious attempt to convert to AF-On/Back Button Focus and a 24-85mm VR I bought used (I needed a lightweight traveling lens for my D700).

This lens hunted like crazy while I kept the AF-On button pressed. I expected it to settle or give up. However focus never settled and the VF rangefinder indicators never ceased to flicker. This didn't happen all the time but frequent enough to drive me crazy. I shoot a lot of static subjects and this behavior rendered the AF-On technique more or less useless for that kind of photography. Switching to AF-S solved the problem, focus was instantaneously acquired but I really wanted to switch exclusively to Back Button Focus and not have to switch between AF-S and AF-C.

I went over the D700 in question, inspected the mirror box, made sure sensors and lens connectors was clean, made all kind of focus tests, using tripod, good lighting and optimal focus targets. Problem persisted and the really bad was how the constant micro adjustments affected focus. Continuous small small corrections, most of the time in focus, but suddenly a greater “jump” where you could actually observe moments of severe out of focus through the VF. AF-On require release priority and releasing during one of those out of focus moments generated an unacceptable rate of out of focus pictures.

I started to suspect the lens and was just about to send it to Nikon for service when I by chance observed a similar behavior from my 105mm f/2.8 Micro under certain conditions! You could suspect the body but this D700 focus perfectly with the 24-70 f/2.8 using the same Back Button Focus technique (with the very same settings). I managed to force the same behavior with the 70-200 f/2.8 VRII but only under very specific circumstances. E.g. use a light pole as focus target, lit from the side so that one side is bright and the other dark with a gradient transition in-between. Zoom until the light pole more or less fill the rectangle representing the active focus censor. Press and hold AF-On while moving the censor slightly up and down the pole. This made AF go crazy in a similar fashion even when trying it out with a D4 (but nothing else did, the D4 AF was rock solid trying the same with the 24-70 f/2.8 for example).

I started to search the Internet for references, maybe someone else experienced something similar? I didn't find much but I stumbled across this thread:

http://www.dpreview.com/forums/post/50774257

I had already tested my lenses on the D700 in question but I never managed to end up with consistent figures and I therefor decided to leave it off. The idea of using LV to acquire optimal focus and then the VF rangefinder arrows to bracket out an interval never occurred to me so I decided to give it a shot with the problematic lenses.

The 105mm ended up with an interval of 17 to -10 and the 24-85mm with an interval of 10 to -1 @ 70mm and 2 to -3 @ 24mm. What to dial in? I ended up using 4 for the 105mm and 3 for the 24-85mm. Both values quite close to zero and I therefor didn't expect any improvements enabling AF Fine Tune. However to my utter surprise, these lenses doesn't hunt like crazy anymore! I can still force AF to hesitate and flicker a bit but not at all like it was before. AF-On is now usable but I have no idea if it was the values I dialed in or just the fact that I enabled AF Fine Tune that made the difference. Everything else is however the same, no other settings changed.

I would not read too much into this but it might help someone else so I thought I better document and share my experience. I haven't had much time to verify my findings yet but I did extensive tests before and after under the same lightning conditions using multiple everyday objects as focus targets (e.g. black cross on a white wall, flowers, a computer mouse on a table, some high contrast objects at different distances outdoor) and it was like night and day. Anyone else experienced something similar?

Nikon D4 Nikon D700
If you believe there are incorrect tags, please send us this post using our feedback form.
InTheMist
Senior MemberPosts: 2,665Gear list
Like?
Re: AF-C problems solved by AF Fine Tune or am I imagining things?
In reply to Robert Palmqvist, 7 months ago

Thanks for sharing.  Did you have a similar experience with the same lenses on your D4?

-- hide signature --

It's more important how an image looks as a thumbnail than how it looks at 100%.
http://inthemistphoto.com

 InTheMist's gear list:InTheMist's gear list
Nikon 1 AW1 Nikon Df Nikon D810 Nikon AF-S Nikkor 14-24mm f/2.8G ED Nikon AF-S Nikkor 24-70mm f/2.8G ED +11 more
Reply   Reply with quote   Complain
Leonard Shepherd
Veteran MemberPosts: 8,752Gear list
Like?
Re: You have not included any images
In reply to Robert Palmqvist, 7 months ago

Robert Palmqvist wrote:

This lens hunted like crazy while I kept the AF-On button pressed. I expected it to settle or give up. However focus never settled and the VF rangefinder indicators never ceased to flicker. This didn't happen all the time but frequent enough to drive me crazy.

When the AF light flickers it means the camera AF has not detected enough good quality detail for the AF to detect the subject - resulting in no viewfinder focus confirmation.

As the lens is old and second hand I would start by carefully cleaning the lens and camera bayonet electric contacts. Doing the resolves a high percentage of AF issues.

I presume you know AF cannot focus accurate on everything, and some lenses have AF somewhat slow for focus tracking fast moving subjects. Sample images often help identify what the problem might be.

-- hide signature --

Leonard Shepherd
Producing good quality photographs, or being good at sport or art, involves a little more than buying appropriate equipment. Practice, some learning and perhaps natural talent often play a bigger role than the equipment in your hands.

 Leonard Shepherd's gear list:Leonard Shepherd's gear list
Nikon D800 Nikon D7100 Nikon AF-S DX Nikkor 18-200mm f/3.5-5.6G IF-ED VR Nikon AF-S DX Nikkor 12-24mm f/4G ED-IF Nikon AF-S Nikkor 16-35mm f/4G ED VR +19 more
Reply   Reply with quote   Complain
Robert Palmqvist
Regular MemberPosts: 447
Like?
Re: AF-C problems solved by AF Fine Tune or am I imagining things?
In reply to InTheMist, 7 months ago

Never thought about mounting the 24-85mm on the D4, it's now done and it didn't hunt at all even with AF Fine Tune disabled (AF just as solid as with the 24-70).

But I dropped by a friend this morning. He just bought a 300mm f/2.8 (from another friend). I mounted it on the D700 and it hunted quite bad (not as bad as the 24-85 before AF Fine Tune, but quite bad). So I assumed it would not hunt on the D4 but it did. Almost as bad as on the D700. I had no time to try AF Fine Tune for the 300m as with the other two problematic lenses. Maybe some other time...

Reply   Reply with quote   Complain
Robert Palmqvist
Regular MemberPosts: 447
Like?
Re: You have not included any images
In reply to Leonard Shepherd, 7 months ago

Thanks Leonard but cleaning the bayonet and contacts was my first action. My AF problems was not due to bad focus targets. The flickering VF "rangefinder" indicators was not due to bad contrast, tricky light sources or subjects. I could quite easily get into a state where these indicator lights flickered like crazy even when focusing on a perfect focus target (like a focus card or a black cross on a white wall). You might think it was due to me not being able to hold still and/or slightly shifting the focus plane but no. I have ruled it out by using a tripod and AF might still hunt. Note that we are not talking about moving targets or bad targets, we talk about static targets with great contrast and camera on a tripod. I still manage to get into a state where AF (while keeping AF-On button pressed and AF-C enabled) continuously micro adjust and never settles (VF "rangefinder" indicators flickers like crazy and focus is never acquired).

This "crazy" behavior is gone after AF Fine Tune is enabled (as described in my first post).

Reply   Reply with quote   Complain
Robert Palmqvist
Regular MemberPosts: 447
Like?
Re: You have not included any images
In reply to Leonard Shepherd, 7 months ago

Ps. I didn't include any images because there is nothing worth looking at (just out of focus images) and I have therefor deleted them over the last couple of weeks (while looking for a solution to my problems). I usually format the card after each session. Would images help in any way? I don't see how images could help in this case, maybe a video of the VF indicators flickering like crazy but I am a bit too lazy to make one (especially now when I found a solution to my problem).

I should add that the lens was bought used that is true but it was not old or dirty. I bought it from someone who just bought a D800 with the 24-85mm. He quickly got cold feet (and some extra money) and wanted to replace it with a 24-70mm f/2.8. The 24-85mm was in mint condition and not used much at all.

Reply   Reply with quote   Complain
olyflyer
Forum ProPosts: 23,343
Like?
Very interesting
In reply to Robert Palmqvist, 7 months ago

Thank you for sharing this. I have not experienced any hunting with my D800 except with the 105/2.8GVR macro lens, so perhaps I'll give it a chance and do the tuning to see if it improves. I also have the 60/2.8G macro lens and that does not hunt in the same situation, and that's the lens I use most, so the 105 hunting didn't bother me that much before, but of course it would be better if it never hunted, so I must try it according to your post.

Reply   Reply with quote   Complain
Robert Palmqvist
Regular MemberPosts: 447
Like?
Re: Very interesting
In reply to olyflyer, 7 months ago

I have used the 105 as a short tele (shooting sports) and had no problems (AF-C but with moving subjects). I also used it for portraits (with no AF problems) and I never had any problems using it for macro (but usually using MF instead of AF for macro). I am not sure I would have noticed anything if it wasn't for my bad behaving 24-85. But I was already on my toes and switched from the 24-85 to the 105 (because of this annoying behavior) when I was on a walk a couple of weeks ago. It was a bright spring day with a lot of shades of brown (here in Sweden).

I was planning on some macro shots (and it worked fine) but kept the lens on since I was frustrated by the 24-85. So I started to shoot with the 105 as I had been shooting with the 24-85 (random pictures in the forest). I have to admit that focus conditions was a bit more tricky than a focus card or a black cross on a white wall but nothing extreme. This is when I experienced a similar behavior as with the 24-85 (same configuration using AF-C and AF-On). And that is why I included it with my 24-85 as one of the "tricky" ones...

Reply   Reply with quote   Complain
Keyboard shortcuts:
FForum MMy threads