100-400 "rear focussing" problem.

mac124

mac124

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It seems my 2nd new 100-400mm might have a rear focussing "issue". Any advice on how to address it? I have included a picture i recently took which shows the focus point and as you can see the wing in the far side of the dragon fly is nicely focussed not the body or more liekly the wing this side. All pictures taken with it seem to suffer the same problem. I have tried tweaking the micro focus settings, i set it more to the Backwards setting? This seems to have improved it slightly but i am still not entirely happy with it. After the 5 week fiasco of returning my last lens back to Canon i am loathed to do it again unless absolutely necessary.

Could i get it "calibrated" anywhere?

dragonfly.jpg
 
Can you not just dial that out using the micro adjust on the camera ?
 
If you're setting the camera at +20 backwards then surely it's focusing where you've told it to. Maybe you need to bring if forwards ?
 
I am not sure, i assumed, rightly or wrongly, setting it more "backwards" pulled the focus back towards me? The manual doesn't stipulate either way.

I will go and retry it with it more forward.
 
Setting positive values shifts the focus further away. Back means to the rear of the subject instead of towards the front. In other words, "+" = more distance, not less.
 
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Get a 1m rule and stick it an an angle about 40 feet away. Focus on the centre of the ruler at 400mm focul length and photograph it. Look at the picture on your pc. Then dial in +20 and look at it again. Then -20 and do the same.

It will show you if you are back or front focusing.

Take a few shots then moving it the way you think.

Always manualy " Off focus " the lens a number of times at each test point to ensure it's not just focus lock problems.

You can use EOS utility to do the checking as it outputs directly in a large format on your screen. If you have a laptop you can use even better.
 
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malla1962 said:
Yes but you say it improved it slightly? how close were you to the dragon fly?
Click to expand...

15, maybe 20 feet?

I have gone through the whole process again and it does seem to need a + number, obviously i messed up somewhere along the process first time around, it seems to need +8 / +9 though it still doesn't seem as sharp as i would expect, maybe i am expecting too much? Tested it at iso100 / F5.6 / 400mm / target approx 25 feet away so it might be better at higher F numbers i suppose.

Haven't had a chance to use it in anger as yet.


ChrisH said:
Get a 1m rule and stick it an an angle about 40 feet away. Focus on the centre of the ruler at 400mm focul length and photograph it. Look at the picture on your pc. Then dial in +20 and look at it again. Then -20 and do the same.

It will show you if you are back or front focusing.

Take a few shots then moving it the way you think.

Always manualy " Off focus " the lens a number of times at each test point to ensure it's not just focus lock problems.

You can use EOS utility to do the checking as it outputs directly in a large format on your screen. If you have a laptop you can use even better.
Click to expand...

Cheers for the tip Chris, i maywell redo it if i can get hold of a metre rule, failing that a tape measure and a plank will come into play. Never thought of doing it like that.

It should focus "properly" as it went from focussing behind to in front of the target at opposite ends of the micro focus scale.

Thanks again for the advice, feel a bit of a numpty now tbh as it looks like it might be my own fault :shrug:
 
mac124 said:
15, maybe 20 feet?
Click to expand...

If we take that to be 5 metres and your subject to be about 8cm then you've cropped this to the equivalent of over 1400mm or >3x your maximum available focal length....it's very difficult to use this as a basis for any focus offset judgement.

Bob
 
mac124 said:
It may have been slightly closer :thinking:, here is the uncropped version if if thats any use :shrug:
Click to expand...

based on my guess at the dragon's length (8cm) then you were around 5.7m away.

DoF at 5.7m with 400mm @ f/5.6 is 4cm total (2cm front and 2cm behind). The outstretched wings of a dragon probably span 7-8cm so, if those were your settings, it's not all going to be in sharp focus and simply down to what the AF sensor picked up on....the wing or the body.

Bob
 
Thanks for that Bob. It just annoyed me that the point i "focussed on" wasn't in focus had the wing closest to the camera been in focus and the body wasn't it wouldn't have bothered me as it would have just been down to the camera picking up the wing not the body of the dragonfly.

I realise now i had messed up the micro focussing and won't really know if its focussing "properly" until i get a chance to try it out.

It just bugs me (no pun intended) that i have yet to get what i consider a sharp picture from this lens after hours of trying & god knows how many test shots. I realise that "better" hardware can sometimes be harder to use and coming from basically a bottom of the range body and low end lens to a 50d and 100-400L lens is a big jump, but should it really be this difficult to set it up?
 
mac124 said:
.... I realise that "better" hardware can sometimes be harder to use and coming from basically a bottom of the range body and low end lens to a 50d and 100-400L lens is a big jump, but should it really be this difficult to set it up?
Click to expand...

You're not the first (or the last) person to suffer a little disappointment and frustration when new gear doesn't give the instant improvement that you expected. Be patient and practice to see what gives the best results and two months from now you'll wonder what it was all about.

Bob
 
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