Backlit subject focus problems with 300 2.8 II

[krisbell]

Hi all,

I am actually in disbelief that I have to even post this question as I have to ashamedly admit to shaking my head on more than one occasion at some of the silly questions I see online - but now I am guilty of the same thing!

Nevertheless I am having real problems with what I assume is poor focus with my 300mm 2.8 II on a 5D3. I have never AFMAd this lens and I am sure that will be the first bit of advice given but it has always been razor sharp with and without teleconvertors since the day I bought it. I am taking pics of backlit squirrels at shutter speeds between 1/250 to 1/1000. They are often pretty stationary while they eat and my lens is well supported (though not on a tripod). I usually use my 300mm with a 2x teleconverter at 1/500 and very rarely get one that isnt sharp. When i took a few shots of subjects that were front lit the lens appeared extremely sharp as usual but as soon as I took a shot of the squirrel the results were almost consistently out of focus/blurry (though not obvious motion blur). I am using a single focus point on the eye (which is dark anyway and also in shade). Has anyone else experienced focus problems with backlit subjects and have any advice?

Cheers, Kris

 

[martti]

Could it be that there is an element inside that is out of alignment and gives disrtortion that fools the autofocus system? I had that with the 70-200L.

 

[krisbell]

Hi Martti and thanks for the response - how would I find this out? Also, would this not mean that any/all shots are out of focus? When I focus on something well lit it seems extremely sharp.

 

[Marsu42]

When i took a few shots of subjects that were front lit the lens appeared extremely sharp as usual but as soon as I took a shot of the squirrel the results were almost consistently out of focus/blurry (though not obvious motion blur). I am using a single focus point on the eye (which is dark anyway and also in shade). Has anyone else experienced focus problems with backlit subjects and have any advice?

I like to shoot backlit subjects, though only with my much cheaper 6d+70-300L. But I think my experience could apply even though: If a very bright spot like the sun's corona overpowers the subject, the af system stuggles. It's rewarding to get these shots done, even though it needs contrast lifting in postprocessing - but the keeper rate is much lower than shooting front-lit sitting ducks.

Imho your options are

• keep trying with multiple shots
• reframe to have more contrast on the subject
• try to fan/occlude the light source that shines into your lens from the side with a reflector or the like - which is hard to do when shooting handheld outside.

In any case, make sure that your lens' front is very clean and try removing a filter, esp. if it's not the most expensive coating. The idea is to get as little light diffusion as possible, enhancing the keeper rate.

 

[krisbell]

Many thanks Marsu, though I do not use a filter, the front glass is perfect and I have the lens hood installed so no direct sun is in frame!

I'm at a total loss to understand what is going on. I snapped probably 50 odd shots of different squirrels, all backlit, but in varying degrees of sunshine and light angle and I managed almost no shots in focus. Even the ones that were just about sharp were nothing like as sharp as I know the lens usually produces, and produces as soon as I point it at something other than a squirrel. Maybe the focus just cant see a black eye set against deep red fur in shadow?

 

[Maiaibing]

Hi all,

I am actually in disbelief that I have to even post this question as I have to ashamedly admit to shaking my head on more than one occasion at some of the silly questions I see online - but now I am guilty of the same thing!

Nevertheless I am having real problems with what I assume is poor focus with my 300mm 2.8 II on a 5D3. I have never AFMAd this lens and I am sure that will be the first bit of advice given but it has always been razor sharp with and without teleconvertors since the day I bought it. I am taking pics of backlit squirrels at shutter speeds between 1/250 to 1/1000. They are often pretty stationary while they eat and my lens is well supported (though not on a tripod). I usually use my 300mm with a 2x teleconverter at 1/500 and very rarely get one that isnt sharp. When i took a few shots of subjects that were front lit the lens appeared extremely sharp as usual but as soon as I took a shot of the squirrel the results were almost consistently out of focus/blurry (though not obvious motion blur). I am using a single focus point on the eye (which is dark anyway and also in shade). Has anyone else experienced focus problems with backlit subjects and have any advice?

Cheers, Kris

Sort answer: if it takes sharp pictures front lit, don't worry that's it more difficult getting sharp pictures backlit - it is!

I use the lens a lot and I take lots of backlit pictures of moving subjects with it. The fact is that the 300 f/2.8IS L II does struggle in this situation. However, I do not think it does more (or less) so than other lenses. One thing I usually do is using AI Servo and to try to "track" onto the subject and "flex" the shutter button until I am sure the focus is right which may take several attempts before shooting a small burst of 3-4 shots (I hope this makes sense).

Happy shooting!

(For fun I attached a picture - surprised how bad it looks unless you click on it...)

 

[Marsu42]

Maybe the focus just cant see a black eye set against deep red fur in shadow?

Yes, that's the general problem - the light behind the subject lowers the contrast so that the camera cannot decide what to focus on. Obviously, this is really worse with lens flare, but in general backlit scenes suffer from this. Using af point expansion might help if the surface is flat, but with eyes you have to rely on a single point.

For further advice and analysis please do upload on of these shots, preferably link to the whole raw so we can look at the pixels.

(For fun I attached a picture - surprised how bad it looks unless you click on it...)

I don't think *this* scene should be a problem for the af, plenty of contrast here (though I didn't see the raw before post-processing). Of course with a thinner dof of f2.8 @300mm, a small af miss really shows while with my 70-300L with f5.6@300mm a little error is ok.

 

[krisbell]

Many thanks Maiaibing and Marsu,

I think that must be it - I am so used to super sharp, easy focus on front-lit subjects that I wasnt prepared for this backlit issue. That backlit shot is a lovely shot but I agree with Marsu that there is plenty of contrast and things for the focus to lock onto. I am quite close to the squirrels but the eye is still an extremely small target within the frame so perhaps that is the biggest issue...in combination with the wafer thin focus plane at f2.8 to make any miss much more obvious. I will upload an example shot when I get round to it but probably wont be for a while as images usually lay dormant on my memory card for months before I get round to uploading them. Never understand how people can take a picture and upload it within hours!

 

[martti]

Pretty impressive shots on Kristian's Flickr pages.

 

[cervantes]

Hi Kristian,

first off all it's nice to see that there are indeed photographers on this site not only gearheads. :
The images on your flickr stream are fantastic! I wonder how many years it will take me to get on your level...

About the focus issues: I use a pretty similar combo - 5D3 and 500 f4 L II and I did not encounter said issues. I'm sure that AFMA has nothing to do with the problem, since you said that only backlit images are affected. As others suggested using some kind of AF point expansion will pretty surely do the trick (I always go with 4-point expansion when necessary). Single point on a black eye sounds not very promising.

Best wishes!

 

[chauncey]

What I would do is...mount that puppy on a tripod and hook it up to your Canon Utility Software to shoot tethered scenario>
take an AF shot before hand>then take a shot tethered, using a manual adjustment available within the Live Shoot part of the software.
Problems will be quickly evident.

 

[krisbell]

Many thanks for the comments/suggestions all - I think I will take a two pronged attack to this. I will try messing with AI Servo vs single shot, I will mess with expanded area AF vs centre point only...and most importantly I will lower my expectations of razor sharp backlit shots 100% of the time!

 

[ifp]

I don't see anything about spot focus. You might want to try that.

My suspicion is that since the AF point is actually larger than the viewfinder's depiction of it, focus is actually grabbing at a different spot than you intend.

 

[garyknrd]

I have that lens, and the 500 II. Both act the same way. I personally try to avoid taking photos in that kind of lighting.
Personally I don't like the photo's either. Years ago I thought it was a problem with the lens. But, the 1d IV and my 7d are the same. The IV has a tighter circle of confusion on the center point I think. It is a little better. But, it is a problem that is very common I think. I Also shoot with other systems now, and it is the same with my other system as well.
Shooting small birds is about the same as a small critter I would imagine.

http://www.flickr.com/photos/avianphotos
http://www.birdsthatfart.com

 

[krisbell]

Thanks for the input Gary - if nothing else it makes me feel better that I am not being completely incompetent. I guess it is just something that even the big whites struggle with. I have tried all the suggestions above and I'm still not getting anything better than a 10% hit rate (if that). For what its worth I also used to avoid any sort of backlighting but now believe that when done well it can produce more impressive and striking images than any front-lit subject.