Low light back focus with 35mm f1.8 AF-S

Hi -

Recently got a D7000 with a 35mm f1.8 AF-S, and am noticing that I'm getting a lot - about 75% - of misfocussed shots when using the camera in low light - evening streetlight, for example.

I have the camera in Single point AF and have tried using both the centre focal point + recompose and the closest focus point in this mode; even tho AF system says it's found focus, when I check on the display and on the computer later, it's focused behind the point I chose. I've tried with and without the AF assist light, and get the same thing. Very frustrating.

This doesn't happen in daylight settings tho.

So - is this a limit of the AF on the camera? Is the camera faulty? Is it the 35mm lens? Can't work it out.

I have an 85mm AF-D too, so will be trying that later to see how it behaves in the same situation.

Any advice / help much appreciated - thanks

You stated your problem in your first sentence, "misfocussed shots when using the camera in low light - evening streetlight". The auto focus system depends on subject contrast for focus lock. Low light or evening street light is low contrast and the camera is looking for the best contrast to lock focus. Unfortunately in low light situations, if it finds a focus lock at all, it may not be your subject. It is one of the weaknesses of the auto focus system you have to learn to work with. The auto focus is through the lens focusing so it won't matter what lens you use the same difficulty with finding a focus lock in low light will exist.

And welcome to the Nikonites Community. A great place to find answers to your questions.

Joseph Bautsch said:

You stated your problem in your first sentence, "misfocussed shots when using the camera in low light - evening streetlight". The auto focus system depends on subject contrast for focus lock. Low light or evening street light is low contrast and the camera is looking for the best contrast to lock focus. Unfortunately in low light situations, if it finds a focus lock at all, it may not be your subject. It is one of the weaknesses of the auto focus system you have to learn to work with. The auto focus is through the lens focusing so it won't matter what lens you use the same difficulty with finding a focus lock in low light will exist.

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Thanks for your reply.

Unfortunately, having carefully tested further, the AF on the camera is not giving consistent results even with indoor daylight –*it will often focus behind my selected focus point.

Also, when I've had the AF light switched on, the camera usually focusses behind the point I've selected. I'd have thought the purpose of this light was to enable the camera to get the correct AF point when the ambient light is too low :-/

This is the second D7000 body I've had, the first being exchanged after the shop checked and verified focus errors. I've used a 5D with a 35mm f1.4 for many years in the same lighting situations with , and I'm finding the AF errors on this body to be too significant to ignore.

I think it will be going to Nikon for repair, but if this is just the limitations of the AF system, then I'll have to change to a different body with more consistently accurate AF. Am I right in thinking the D300s or D700 have more robust AF?

The AF light is only an aid to focusing in low light but not a absolute answer. This low light focusing "limitation" is found in all TTL focusing systems regardless of the make or model. As I stated above it has to do more with subject contrast than anything else. In this case you may need to have the focusing system realigned by Nikon or a Nikon repair shop. Unfortunately I've read a lot about focusing problems with the D7000. I don't know that the AF system in the D300s or the D700 is any more robust. Changing to those models may solve your problem only because Nikon is not having the same AF technical problems as with the D7000. The majority of these models being sold by Nikon are fine and are great cameras. But a few seem to be getting through their quality control needing this adjustment.

Sounds to me like you need to send it in. I have the D7000 and love the AF system. It has been spot on in all types of lighting. I do a lot of low light shooting in black sooty fire scenes and I feel the D7000 does a better job than my previous D70, and D300.

I'm shooting with the same lens/body combination. I took several pictures of high-contrast objects in very low light, and the focus was perfect. The next morning I took pictures of my black cat in the morning sunlight, and they were all blurry. Jpseph's post helped me understand why this is so: there's no contrast when I shoot my black cat from very close up.

Thanks for the replies -

Yep, understood about the need for a certain amount of contrast in locking onto the correct focus point. I've been having problems with getting focus on good contrast subjects indoors tho.

Nikon support has taken a look at some of the photos and asked me to send the body in for AF calibration, so I'll be sending it off soon and hopefully it will come back much improved

Thanks again -

Hello!

I have the EXACT same problem as you. I've been going on about this for almost six months now and haven't found the reason for it! I've only tried this one D7000-house though but I also sent it back to Nikon (twice!) but with no faults found. I shoot a lot of indoors and low light situations and most of the times the focus end up about 5-15cm behind the focus point.

I've also sent the house along with my Sigma 30/1,4 for correction -they calibrated the lens +15. The lens had perfect focus before on my D80. Even though the lens is corrected it's far from perfect. My first choice lens is the Nikon 17-55/2,8... and even with that lens the house seem to suffer from a slight back focusing problem.

Can you correct your problem with the AT-finetune in the menu? I can't. The finetune makes no visual difference.

What did the people at Nikon say about your kit as it was returned?

Hi -


Yes, seems like I'm not the only one with a problem.


Camera was calibrated, sent back and focuses well in daylight. Below a certain light level tho, the AF still often says it has got focus when it hasn't. I never had this problem before - my previous camera (a 5D) would only confirm focus if it had it - or at least, much much more consistently than the D7000.


I'm waiting for a new body to come out, or else sell it all and get something else. I just don't think it's good enough.

I am having the same issues. I bought the camera refurbished, I wonder if this is why it was returned. Sending mine in tomorrow...
This is agonizing as I returned the D90 which was fantastic for this D7000 piece of poop. So many people talking about these issues on the web, I'm shocked Nikon hasn't owned up to it.

Bens,

I dealt with this issue. I sent the camera back to NIKON For repairs and EVERY lens I own is spot on but my 35mm 1.8. Please make sure you are having this issue with all of your lenses before you give up on your camera... Could just be this lens


This camera is amazing!!! If its not what you were desiring, send it back to nikon for repairs and demand service

Hope this helps

Courtnie

I agree with Courtnie. Test your lenses. I have found that my 35mm f/1.8 focus slightly beyond my subject but not with my others. After it tries to focus I just simply manually focus it forward to correct it. Lame, but it works...

Harth,
You could fine tune it!!! Then you wouldnt have to manually focus...

Also, reading Mastering the D7000 chapter on the auto focusing system helped me a ton. (I had to read it three times before it really clicked)

Ok cool, I'll take a look at that section this evening. Hopefully it can help me as well.

I had similar feedback that it was a problem with the 35 f/1.8. But I also had poor focus accuracy with the 24 f/1.4 and returned that lens.

So I sold my D7000 and got a Sony A77 instead - bit larger, not quite as fast or solid, photos a bit noisier at high ISOs - but, along with all its other benefits, its focussing – especially in low light – is fast and accurate. Very happy.