70-200 f/4L focus problems - opinions please...

[JusSmith]

I'm still not convinced by my 70-200mm f/4L after accepting that camera shake may have been an issue in the past.

This first shot is at f/4.5, 1/200s, iso100 on a tripod
http://www.pbase.com/jussmith/image/42640255/original.jpg

Same shot, but al f/11 (1/25s)
http://www.pbase.com/jussmith/image/42640256/original.jpg

The 70-200 f/4L is supposed to be sharp from f/4 from what I've read, is this true? My first guess is some back focusing problem, so that once the DOF is extended with the smaller aperture, the subject becomes in focus?


This was shot at f/4, 1/800s, iso100, rested on a car roof, centre point AF (I've marked this and 4 others)
http://www.pbase.com/jussmith/image/42640257/original.jpg

100% crop at the centre (supposed focus point) gives...
http://www.pbase.com/jussmith/image/42640258/original.jpg

...but to the right, not far from the right-hand focus point I get...
http://www.pbase.com/jussmith/image/42640259/original.jpg

I also took a picture of a loan tree (not posted) which seemed to be nicely sharp. The difference being it had nothing either side of it that was close. Could it be that the lens is choosing another point of focus when one is near and choosing the expected one when it cannot find anything else around the centre point?

Thanks very much in advance for any comments, greatly appreciated.

[tim]

Are you using the centre focus point?

You should print out one of the focus test charts and try that instead of random shooting. I don't have a URL sorry, but you might be able to find it with a search. The one i'm talking about's at the Canon japan site, but there are others that will do the same thing. At a pinch try what I did in this thread (http://photography-on-the.net/forum/showthread.php?t=66959).

[JusSmith]

Are you using the centre focus point?

You should print out one of the focus test charts and try that instead of random shooting. I don't have a URL sorry, but you might be able to find it with a search. The one i'm talking about's at the Canon japan site, but there are others that will do the same thing. At a pinch try what I did in this thread (http://photography-on-the.net/forum/showthread.php?t=66959).

Yep, centre focus point always.

I guess the focus test charts will tell me where the focus point is, but being realistic, if this lens won't focus on "random" shots, there's no point having it just to take pictures of test charts!

Cannot see why the lens would have trouble focusing on a white number plaque?

[Cadwell]

I can't see why it would have trouble either. To me your lens looks faulty.

[tim]

Sounds to me like you should return it from where it came from, or get it serviced by Canon.

[mr.photoguy]

yeah, I would send it back, if your not satisfied with it.
My lens is sharp from f4 and up.
good luck.
b

[JusSmith]

What minimum shutter speeds would you guys recommend to overcome "normal" shake (not sure how steady I am relative to others) when hand-holding the 70-200 f/4L?

[Andy_T]

'rule of thumb' ... 1/effective focal length.

That would be 1/125 (there is no 1/112) on the wide end and 1/500 (instead of 1/320) on the long end.

Best regards,
Andy

[KenE]

I've been battling this problem with a 17-40L. Sent it back to Canon for repair once, shot test patterns for focus accuracy (it seems to be all over the place through focal lengths and apertures), and now will be sending back the body with the lens for calibration after that being suggested by a few shops and lens rental places. Going to miss the 20D sorely in transit.

OTOH, the 70-200f/4L is having no problems whatsoever.

[Medic1]

I can't see why it would have trouble either. To me your lens looks faulty.

I second that....I have never really had any problems with my 70-200 f4L. That being said, I did once have a UV filter that for some reason screwed my image quality despite being a Pro Hoya filter. You aren't using a filter by chance are you?

[SeanH]

Text looks good to me, but I'm gonna call "camera shake" on the other one. And as far as the bricks & window pane being sharp.........I don't know, however I have noticed that light objects with less detail sometimes seems sharp even when there not.

[rent]

JusSmith: i can do some test shots with my 70-200f/4L & 10D for you to compare with (when i get home later this evening). could you tell me what is the focal length used for your first two sample images (the ones with the text) and also what is the approximate focusing distance.

also, are the two sample images a crop of the original? if so, what is the dimension and resolution of the crop?

based on the information you provided on the shot with the house, it looks like it's back focusing a bit (20 is fuzzy, but window behind it is in focus), that may also explain why the text at f/4.5 is fuzzy because it's actually focusing behind it.

Thanks!

-alex

[JusSmith]

I second that....I have never really had any problems with my 70-200 f4L. That being said, I did once have a UV filter that for some reason screwed my image quality despite being a Pro Hoya filter. You aren't using a filter by chance are you?

Spot on, I have the Hoya Pro UV, I will try it without it on!

[JusSmith]

JusSmith: i can do some test shots with my 70-200f/4L & 10D for you to compare with (when i get home later this evening). could you tell me what is the focal length used for your first two sample images (the ones with the text) and also what is the approximate focusing distance.

also, are the two sample images a crop of the original? if so, what is the dimension and resolution of the crop?

based on the information you provided on the shot with the house, it looks like it's back focusing a bit (20 is fuzzy, but window behind it is in focus), that may also explain why the text at f/4.5 is fuzzy because it's actually focusing behind it.

Thanks!

-alex

Alex - they were all at 200mm. I took at look at all my 70-200 shots again last night and this problem seems to only occur at 200mm, at 70mm the shots look fine, but then the DOF will be greater at 70mm, won't it? I have some shots at 200mm which are in focus, but this only happens when all the subject is close to centre focus point and there is nothing around it near, ie a lone tree with background miles away.

[PhotosGuy]

Have you tried to do something like this?