inconsistent focus with 70-200 2.8L mkI

ive been playing around with my 70-200 and it seems as if i have inconsistent focus sharpness...

sometimes it looks pretty good and other times there are definitely some fuzzy looks...

is this something that could be remedied with a trip to Canon? id like to get a good focus target and shoot some pics off a tripod to confirm my suspicions first of course but definitely need some peace of mind...

Ltdave wrote in post #14842192
ive been playing around with my 70-200 and it seems as if i have inconsistent focus sharpness...

sometimes it looks pretty good and other times there are definitely some fuzzy looks...

is this something that could be remedied with a trip to Canon? id like to get a good focus target and shoot some pics off a tripod to confirm my suspicions first of course but definitely need some peace of mind...

I'd definitely run it through a quick test on a tripod before going into too much worry. I notice that sometimes I'll forget about the focal length I'm shooting at, and then when I review my pics later I'm wondering why my 200mm at 1/80th of a sec isn't looking as sharp as I like. Not to say that's the case here, but good to do a controlled test to see if you can reproduce the problem.

I just bought a Sigma 70-200 OS HSM. I can get some fuzzy shots by shooting at 200mm, f/2.8 and focusing at 10 feet. DOF is like 1/4" under those circumstances. What are the shot parameters? Could you be asking too much of the lens? As NightDiver13 said, some controlled tests are in order.

yes, i very well could be...

thanks for the input everyone...

DOF at 10' at 2.8 is actually about 2 feet, not .25"

Test at f/4, virtually every shot should be spot on.

tompfeiffer wrote in post #14842999
DOF at 10' at 2.8 is actually about 2 feet, not .25"

Test at f/4, virtually every shot should be spot on.

Please back up that statement. According to this web-site: http://www.dofmaster.c​om/dofjs.html DOF with a crop sensor is as follows:
f/2.8, 10', 70mm - DOF = 8 inches.
f/2.8, 10', 200mm - DOF = less than 1 inch. (Edit on this line, 200 not 2000 as originally mis-typed)

As supporting evidence I submit the attached photograph. Shot with 60D and Sigma f/2.8 70-200 OS HSM. ISO=100, f/2.8, 200mm, direct flash from a 550EX, focus is on the building above the the second "I". The wine bottle is a measured 10 feet from the sensor plane. The biscuits are 4" behind the front of the wine bottle, clearly OOF. The pop bottle is 3" in front of the wine bottle, again clearly OOF. The wooden chair is 12" behind the biscuits. There is very clearly nothing approaching 2' DOF. The "G" on the wine label is out of focus, as is the small printing on the left edge of the label. As you can see, they are less than an inch apart, front to back, so DOF is less than 1". This does not verify the web-sites calculations, but it most certainly does corroborate them.

If a f/2.8 lens really delivered 2' DOF at a focus distance of 10', nobody would ever buy one. Blurred-out backgrounds would be impossible. Also, if DOF were 2 feet at a focus distance of 10 feet and the lens could not produce a good picture, I would assume the AF is broken.

@TSchrief May want to edit your post for 200 ..
And I would suppose the aperture blades were stuck/broken and thus stopped down with a 2 foot DOF @ 10 feet. But I guess - something broken is still something broken.

wayne.robbins wrote in post #14844613
@TSchrief May want to edit your post for 200 ..
And I would suppose the aperture blades were stuck/broken and thus stopped down with a 2 foot DOF @ 10 feet. But I guess - something broken is still something broken.

My wife is constantly telling me not to proof-read my own writing. Thanks for catching that.

3 photos...

ISO 100
distance of about 25'
Av exposure mode

on a tripod (not a GOOD tripod but a pretty close to USEABLE tripod lol)...

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

Couple of questions:

1. What body are you using?

2. Why would you choose f/32 for ANY shot?

3. Did you use the timer shutter release AND turn OFF the IS on the lens during tripod use?

Comments: The 70-200 f/2.8L should be really sharp at f/2.8 - f/11; 1/6" and 1/50 are pretty slow shutter speeds. The rule of thumb for shutter speed is like twice the focal length used. At 200mm you should be around 1/400.

dave

The f11 and f8 shots look fine. The f32 shot isn't surprising, even if you used a faster shutter. You say sharpness is inconsistent. Is that something you notice under certain circumstances? When you review your images, do you notice a trend of which ones aren't sharp? I ask because three shots taken at very different settings isn't enough to gauge if you're having consistency issues.

Ltdave wrote in post #14844817
3 photos...

At f/32 you are pushing the resolving power of a lens. Diffraction will make the image look soft (or out of focus). Did you turn off IS when using the tripod? That can also be a contributor.

I will say I've seen the same thing with my 70-200 MKII. I've put it on a tripod, remote release, subject is a non moving object.

focus, take shot, manually unfocus it them have it refocus. If I do it over and over some shots are spot on some are not. sent to canon and they said they fixed it. Still same problem exist. I could even sit there and just tap the autofocus button without touching anything else while it was on a tripod and watch the focus point change around.

might be just the way it is. Not sure though.

[QUOTE=TSchrief;148431​98]Please back up that statement. According to this web-site: http://www.dofmaster.c​om/dofjs.html DOF with a crop sensor is as follows:
f/2.8, 10', 70mm - DOF = 8 inches.
f/2.8, 10', 200mm - DOF = less than 1 inch. (Edit on this line, 200 not 2000 as originally mis-typed)

http://2.bp.blogspot.c​om …KCuWf04MxG0/s16​00/DOF.jpg

But that's actually for a 50mm lens, at 70mm f/2.8 it's only about a foot, but still not .25". See here:
http://www.johnhendry.​com/gadget/dof.php

Sorry for the confusion.

On tripod and with a hefty lens at 200mm, the vibration from the shutter is enough to cause blurry pictures like this. Did you use lens collar, mirror up, 2 sec shutter, IS off and on solid ground?