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Thread: Low light AF performance..who is the culprit?

  1. #1

    Default Low light AF performance..who is the culprit?

    Recently I've been shooting in really low light conditions..it's akin to shooting crowd in a concert with only stage lights illuminating the faces..whilst shooting f2.8 at ISO3200 giving 1/25s can give good images..that's not my concern here..shooting in such conditions is never easy and I'm pretty happy with the images that I can capture..

    My real concern is the AF when shooting in such conditions..it's very slow to lock on..I'm using the Sigma 17-50 f2.8 HSM on Canon 50D..let's just say I cannot use the flash and thus AF beam assist is out of the question..without much contrast to focus on..the lens AF is having a hard time finding a lock..sometimes it takes almost 3-5 secs to get focused..

    I've known that Sigma lens are not well-known for their low light AF performance..but it can't be that bad right? I'm starting to think if my 50D could be the cuplrit..it is a 3yrs+ old body no matter what..or could it be that the 2 is not a good combo(though this will be very far fetched!)? Or I just have to accept that this is always gonna be a problem shooting in low light and I should just live with it?

  2. #2

    Default Re: Low light AF performance..who is the culprit?

    Nothing wrong with your gear. This is the situation in low light - lens keeps hunting and difficult to lock on. Manual focus would be a better option.

  3. #3

    Default Re: Low light AF performance..who is the culprit?

    Quote Originally Posted by kkgoxplore View Post
    Nothing wrong with your gear. This is the situation in low light - lens keeps hunting and difficult to lock on. Manual focus would be a better option.
    Manual focusing in lowlight would be better and definitely quieter not to mention less frustrating. Pentax has this option call Catch in Focus aka Focus Trapping where even in Manual Focusing mode, it will automatically take picture the minute it senses the image is sharp enough. Not 100% reliable but good enough when beginning to Manual Focus.
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  4. #4

    Default Re: Low light AF performance..who is the culprit?

    There are numerous factors and factor combinations for low-light AF errors other than brightness of the subject. You can consider these factors;

    1. Color and quality of the light. Some cameras fail on tungsten lighting, even bright colorful lights can sway certain cameras.
    2. Specific lenses. Some lenses perform well in low light, some good in dim light but specifically not tungsten light. This is due to chromatic abberations.
    3. AF Calibration. Contrary to popular believe there is no such thing as perfect calibration. What may be perfect DOF optimisation in normal lighting may be slightly off in other lighting. Experiment and compensate using AF fine-tune to your own taste and habits. For a zoom lens, calibration at the tele-end may be a massive fail for the wide-end.

    A canon technician told me once about 5D Mark II and green colours being a bad match for the AF system and can be tricky to focus on. Take this as a hint to how stage lights can be troubling for your camera since 50D is from the same generation.
    Last edited by surrephoto; 1st January 2012 at 11:35 PM.

  5. #5
    Deregistered allenleonhart's Avatar
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    Default Re: Low light AF performance..who is the culprit?

    Quote Originally Posted by SmOcKxY View Post
    Recently I've been shooting in really low light conditions..it's akin to shooting crowd in a concert with only stage lights illuminating the faces..whilst shooting f2.8 at ISO3200 giving 1/25s can give good images..that's not my concern here..shooting in such conditions is never easy and I'm pretty happy with the images that I can capture..

    My real concern is the AF when shooting in such conditions..it's very slow to lock on..I'm using the Sigma 17-50 f2.8 HSM on Canon 50D..let's just say I cannot use the flash and thus AF beam assist is out of the question..without much contrast to focus on..the lens AF is having a hard time finding a lock..sometimes it takes almost 3-5 secs to get focused..

    I've known that Sigma lens are not well-known for their low light AF performance..but it can't be that bad right? I'm starting to think if my 50D could be the cuplrit..it is a 3yrs+ old body no matter what..or could it be that the 2 is not a good combo(though this will be very far fetched!)? Or I just have to accept that this is always gonna be a problem shooting in low light and I should just live with it?
    u can disable flash fire, but still enable af focus beam, which would solve ur problem.

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    Last edited by allenleonhart; 2nd January 2012 at 09:22 AM.

  6. #6

    Default Re: Low light AF performance..who is the culprit?

    Go manual and maybe shoot a cluster of shots when you think you got the focus right if you are not confident with your manual focus skill. However, in my case, I do realize that some of my cheaper lens (canon 50mm 1.4) have a harder time to find the focus as compared to more expensive ones (canon 100mm 2.8 macro) under low light. However, my 50mm is rather old (more than 5 years) and I've went for cleaning before (though it was done by canon, I always believe internal cleaning of lens is not good for the lens).

    Maybe the lens does affect this or maybe it's just the age and advancement of technology. I'm not very sure.

  7. #7
    Moderator Octarine's Avatar
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    Default Re: Low light AF performance..who is the culprit?

    AF sensors need light, simple as that. If there is not enough of it then they cannot work properly. What your eyes (and your brain as image processor) consider as 'still sufficient' is too low for your camera.
    Edit: Found this article not long ago https://www.lensrentals.com/blog/201...us-often-works
    Last edited by Octarine; 2nd January 2012 at 02:13 PM.
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  8. #8

    Default Re: Low light AF performance..who is the culprit?

    Quote Originally Posted by SmOcKxY View Post
    Recently I've been shooting in really low light conditions............let's just say I cannot use the flash and thus AF beam assist is out of the question
    You didn't specify what exactly your conditions are, so, apart from what allenleonhart said regarding AF beam assist without using flash, I dunno if you can use a torch light with a tight beam (there are those with focusing) to give enough light for focusing, then switch it off and fire. I do that sometimes. And if you need it to be less distracting, put a red cellophane over it. But like I said, I don't know your conditions, so it might or might not be an option at all.

  9. #9

    Default Re: Low light AF performance..who is the culprit?

    As others have already stated, low-light situations are hard for all AF systems. One partial solution used by some event shooters is to assign AF to the "AF-on" button ("*" button on older Canon XXDs) only, so you can shoot a group of shots with the subject at the same distance without the AF hunting between shots.
    BTW the 50D has pretty darn good AF.

  10. #10
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    Default Re: Low light AF performance..who is the culprit?

    3 secs to hunt in low light conditions is normal. After 5 secs or so, the camera AF may even give up.

  11. #11
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    Default Re: Low light AF performance..who is the culprit?

    The true culprit for AF hunting is lack of contrast. You try auto focusing on a evenly well lit pure white / any solid coloured wall and you'll find the AF hunting as well. How our eyes see detail and how the camera sensors look for sharpness is the same, of course due to the mechanics human beings are a lot better.

    Low light will give low contrast, help your camera AF as much as you can by looking for contrast in the frame.

  12. #12
    Deregistered allenleonhart's Avatar
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    Default Re: Low light AF performance..who is the culprit?

    Quote Originally Posted by foxtwo View Post
    The true culprit for AF hunting is lack of contrast. You try auto focusing on a evenly well lit pure white / any solid coloured wall and you'll find the AF hunting as well. How our eyes see detail and how the camera sensors look for sharpness is the same, of course due to the mechanics human beings are a lot better.

    Low light will give low contrast, help your camera AF as much as you can by looking for contrast in the frame.
    seconds this.

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