My 100-400 is Not focusing consistently specialy when the light is not optimal

[rpt]

My 100-400 is not focusing consistently specialy when the light is not optimal. I have done the MA three times now and I am not happy with the results. There does not seem to be a consistent behaviour if the light is not optimal. If I shoot a subject in sunlight, it is sharp and focuses correctly. When I shoot say a hawk in a tree with the sun at 11 o'clock and the sky seen through the branches, although the bird is clear and I shot the bird with centre point focus (and I am quite still - shot over 3000 shots of black kites with my rebel and the same lens) and I can swear I did aim right   the camera somehow does not focus on the bird...

When I shoot with my 24-105, the camera focuses correctly. So the camera does not seem to be at fault. It just occurred to me that I should probably clean the contacts. However, if that does not fix the problem, I am thinking of taking the lens to the Canon repair centre and have them look at it. The lens is almost 5 years old and has never been serviced.

Does anybody have any other suggestions? Has anybody experienced anything similar?

Look forward to your advice.

Thanks in advance.

[Mt Spokane Photography]

A rebel can be difficult to use for focusing on tough subjects, in your case, it might also be camera related.
 
You can check the lens by mounting it on a tripod and repeatedly focusing on a target, resetting the focus to mfd or infinity before each shot.  All lenses will have some variance, and occasionally, totally miss focus, but it should focus accurately most of the time.
 
lenses can have internal issues that cause erratic focusing.  If its new, exchange it, otherwise, have it checked by Canon.
 

[rpt]

A rebel can be difficult to use for focusing on tough subjects, in your case, it might also be camera related.
 
You can check the lens by mounting it on a tripod and repeatedly focusing on a target, resetting the focus to mfd or infinity before each shot.  All lenses will have some variance, and occasionally, totally miss focus, but it should focus accurately most of the time.
 
lenses can have internal issues that cause erratic focusing.  If its new, exchange it, otherwise, have it checked by Canon.

My rebel shots with the 100-400 were good but that was 2 years back. Have not shot much with the 100-400 for the last few years. Sorry, did not mention this problem is with the 100-400 on my 5D3. AFMA was done with each setting that I tested, I de-focused and took 3 shots with the 2 sec timer (and naturally, the camera was on the stand). The 5D3 and 24-105 focuses correctly so I believe it is the 100-400 and not the 5D3...

[lol]

Is the AF of the 5D3 picking something other than what you think? Even if you're only using the centre point, it's effective area can be bigger than you think. This is particularly troublesome if the subject is relatively small or low in contrast compared to something in the background.

[rpt]

Is the AF of the 5D3 picking something other than what you think? Even if you're only using the centre point, it's effective area can be bigger than you think. This is particularly troublesome if the subject is relatively small or low in contrast compared to something in the background.

Is it even bigger than the outer square? The black outer square seemed smaller than the bird...

Thanks for replying.

[Kernuak]

Have you tried playing around with different focusing and tracking settings? From experience with teh 7D, which has a less complex system, when the subject is small in the frame, spot focus often gives better results. If you add in the different tracking scenarios, then you may need to experiment to get the best out of the focus system on the 5D MkIII. What works wiht the 24-105 may not work with the 100-400, because the scenario may be different (at the very least, the subject will be further away). Also bear in mind, that with a longer telephoto, you are compressing the atmosphere between camera and subject, so you will get greater problems with pollution affecting image quality. I spent quite some time trying to understand why some days, I just couldn't get a sharp shot with my 7D and 300 f/2.8+1.4x extender, when other days the combination was sharp. It turned out it was due to the compression of heat haze and moisture, as on each occasion, the subject was low to the ground and there had been mist earlier in the day.

[Marsu42]

Is the AF of the 5D3 picking something other than what you think? Even if you're only using the centre point, it's effective area can be bigger than you think. This is particularly troublesome if the subject is relatively small or low in contrast compared to something in the background.

I see you've got many camera bodies, so maybe you can answer this, because I am experiencing exactly what you are saying on my 60d:

If the spot I want to focus on is very tiny inside the af frame (like focusing on the eye of an animal with side eyes looking towards me) and large aperture, it's much better to shoot, refocus, shoot, refocus, ... than to rely on the af getting it right.

Is this "too large af rectangle" problem any better on the 5d3 (or 5d2 if we're at it) in comparison to an aps-c like my 60d?

[neuroanatomist]

Is it even bigger than the outer square?

Yes, it is.  Here's an approximation of the standard and spot AF compared to the little black box in the viewfinder for the 7D (relative size is likely equivalent on the 5DIII):

[rpt]

Have you tried playing around with different focusing and tracking settings? From experience with teh 7D, which has a less complex system, when the subject is small in the frame, spot focus often gives better results. If you add in the different tracking scenarios, then you may need to experiment to get the best out of the focus system on the 5D MkIII. What works wiht the 24-105 may not work with the 100-400, because the scenario may be different (at the very least, the subject will be further away). Also bear in mind, that with a longer telephoto, you are compressing the atmosphere between camera and subject, so you will get greater problems with pollution affecting image quality. I spent quite some time trying to understand why some days, I just couldn't get a sharp shot with my 7D and 300 f/2.8+1.4x extender, when other days the combination was sharp. It turned out it was due to the compression of heat haze and moisture, as on each occasion, the subject was low to the ground and there had been mist earlier in the day.

Since the bird was sitting still, I shot it in 1 shot mode and not the servo settings. Hence I did not experiment with any of the other focusing settings. I did my usual acquire focus, AF and recompose. It worked for objects getting good light.

Also the bird was about 25 mtr from me in a tree and I could not see any visible pollution or thermals. Also it was probably about 7 mtr up...

Thanks for the response. If anything else strikes you do share.

[rpt]

Is the AF of the 5D3 picking something other than what you think? Even if you're only using the centre point, it's effective area can be bigger than you think. This is particularly troublesome if the subject is relatively small or low in contrast compared to something in the background.

I see you've got many camera bodies, so maybe you can answer this, because I am experiencing exactly what you are saying on my 60d:

If the spot I want to focus on is very tiny inside the af frame (like focusing on the eye of an animal with side eyes looking towards me) and large aperture, it's much better to shoot, refocus, shoot, refocus, ... than to rely on the af getting it right.

Is this "too large af rectangle" problem any better on the 5d3 (or 5d2 if we're at it) in comparison to an aps-c like my 60d?

I was focusing on the back of the bird. Not the eye - so that should not have been it. As neuro points out below, the spot is more a blotch! What lens do you use with the 60D where you are experiencing this?

Wen you say "shoot, refocus, shoot, refocus,..." do you mean manual refocus?

[rpt]

Is it even bigger than the outer square?

Yes, it is.  Here's an approximation of the standard and spot AF compared to the little black box in the viewfinder for the 7D (relative size is likely equivalent on the 5DIII):

Thanks. So I guess I will do some testing with my 300D this Saturday.

[keithfullermusic]

I have this lens and a 50D.  I had to MA the you know what out of it.  Still, when fully extended and objects are far away I have to shoot at f/7.1 or smaller.  If I do, the images are sharp as can be.  If I don't, they are usually blurry.  When using this lens I usually start at f/7.1 and ISO 400 then go from there.  Hope that helps.

[LSV]

I also have this lens and I'm a newbie, so please forgive if my suggestion is simple. Have you switched the setting on the lens to 1.8m-infinity or 6.5m-infinity as appropriate for the situation?

[rpt]

I have this lens and a 50D.  I had to MA the you know what out of it.  Still, when fully extended and objects are far away I have to shoot at f/7.1 or smaller.  If I do, the images are sharp as can be.  If I don't, they are usually blurry.  When using this lens I usually start at f/7.1 and ISO 400 then go from there.  Hope that helps.

Thanks. I will shoot at f8 or f11 and check.

[rpt]

I also have this lens and I'm a newbie, so please forgive if my suggestion is simple. Have you switched the setting on the lens to 1.8m-infinity or 6.5m-infinity as appropriate for the situation?

Yes, it is set at 6.5m-infinity ans the bird was far away - 25m or so. Thanks. Hope you are enjoying your lens