Opticallimits

Full Version: focus problems with 100mm macro or my lens is faulty ?
You're currently viewing a stripped down version of our content. View the full version with proper formatting.
hi all,

Today my 100mm macro has had her first "stress test"

I was shooting some fashion portraits, and as you can imagine I was often usingit wide open, I wasn't shooting in burst mode, but I was taking merely 10-20 shots every minute.

focus set to one shot, central AF point and recompose.

I nused 50f1.4 17-55f2.8 and mostly 100mm macro.

focus hit rate was 100% with EFS-17-55 and the 50f1.4, but not with 100mm macro where it was barely 50%, you may argue that DOF is thinner for the 100 macro, so it is my 30D who can't handle it, however I am not quite sure about it.

Is it a common problem with this lens ?

if it is then this would accelerate my decision to migrate to the new IS version.
Which 100mm macro do you use?



Eventually, you could verify your results with a more formal focus test

(with 5 batteries / bottles / something similar) for the distance those

shots were mainly made.



Generally, macro lenses tend to have a slower focus, but aren't less

accurate.
Focus then recompose will lead to errors, which might be significant in shallow DoF usage. Like Rainer suggests, check that your lens/body combination doesn't have a focus accuracy problem. If that is ruled out, then you have probably gone beyond the limits of focus and recompose.
[quote name='Rainer' date='10 June 2010 - 07:33 PM' timestamp='1276187635' post='422']

Which 100mm macro do you use?



Eventually, you could verify your results with a more formal focus test

(with 5 batteries / bottles / something similar) for the distance those

shots were mainly made.



Generally, macro lenses tend to have a slower focus, but aren't less

accurate.

[/quote]

in focus test it did pretty well, this camera has usually not focus problems, however today in the stress test, it just didn't perform well

Guest

I used to have the non-L 100 until I was given the L one for my birthday (lucky me). The old one focussed just fine. There's not that much difference between the old one and the new one; the new one in my tests gives a slightly better and contrastier result wide open and has IS. It's preferable, but the expense is quite high and I don't think I would have upgraded on my own.



If your careful tests reveal that it focusses fine, there is no point getting it calibrated either.



So I'm guessing that it may be, as others have indicated, error due to focus and recompose.



There are 2 sources of error with this:



the first is that you are probably focussing on the eye, which is is likely in the upper part of the frame.

If you point the centre AF point at the eye, and then recompose with it pointed lower, the distance between sensor plane and the eye has changed slightly. Enough to be noticed in some applications. You could try using the uppermost single AF point. Even though it's not cross-type it might work better.



The other source of error in thin DOF photography is slight swaying forward and backward by the photographer or the subject after focus lock and before exposure. The more recomposition, the longer the time between them so the more chance of sway.

Guest

Toni, what were the shutter speeds like? I have this lens and it's usually spot on using auto-focus. Most of the time when there are unsharp pictures, it's down to camera shake in my case.
it seems i am blaming the lens for my own errors, I pushed things too far, a very shallow DOF, focus and recompose on a moving subject.



will be more careful sinday and will upload somethong here
Today I did another photoshoot knowing my gear limitations.

Only 30D central autofocus point can cope with fast glass....

one should be very careful when focusing and recomposing

I suffered a little with my gear today but the result is marvelous, you can enjoy this sample picture, taken with 100mm macro @f2.8 golden reflector plus fill flash



[Image: gallery_5426_21_102756.jpg]