IS blurry pictures

[East Wind Photography]

Yes lenses do wear over time and AF becomes less accurate and can drift slightly.  Usually takes a lot of shots and abuse but it's all mostly mechanical and parts do wear.  I would check the AFMA adjustment to make sure it hasn't drifted again.

One quick test to check things out, with and without IS, is to take shots of a newspaper taped on a wall.  Back up until you reach the resolving limit and can just barely read the fine print at 100% zoom.  try shots with and without IS at the same shutter speeds and compare.  Use a tripod just to eliminate the human part of it.  YOu can also do that to check AFMA setting and see if it's drifted.

Might not be the IS at all.  Could just be normal wear on the AF system.  Have you tried a micro focus adjustment to see if it's front or back focusing?

Thanks everyone for your responses

Can af wear over time? Can accuracy decrease over time?

I know my 7d front focuses by 8 mfa points following a service by canon (grrr) but I've adjusted for that

[atosk930]

a pretty interesting read

http://www.pentaxforums.com/reviews/long-exposure-handhelds/introduction.html

ignoring the forum it is posted on, click through the various pages of techniques

[Sporgon]

Well it depends on how blurry you mean. I've noticed that above speeds that I couldn't hand hold steady the images can be less sharp with IS than without. This effect seems to be random. On the 24-105 at say 50mm I would always have to use IS up to about 40th. Between 40th and 125th I tend to shoot some IS on, some off. Again talking 50mm focal, I can see the difference in sharpness of an image taken at 200th when hand held or from a (very) rigid tripod.

Sometimes I've even got a sharper image hand held with 50 1.4 at 30th than an IS lens - but again it's very random.

It's a strange thing is camera shake, really quite difficult to eliminate altogether, as the proud owners of the D800 are finding out 

Are the effects of shake / movement exaggerated in a dense ( v high res) chip ? Maybe some of the tech bods can shed some light.......

[Studio1930]

I would test that lens with all setting the same and shooting fast like 1/500 or faster.  Shoot the same stationary object and shoot maybe 25 shots with IS on and 25 shots with IS off.  Look at the 50 shots and see if the IS is making things worse.  You could expand this test and try it at slow shutter speeds and way faster shutter speeds.  .......or you could send it in to be checked out.

Personally I love IS as it steadies my viewfinder if nothing else and I leave it on all of the time.  I have very sharp shots at 1/1000 or faster but I know that the IS version in a lens makes a difference as well.  My 70-200 f/2.8 IS II and my 200 f/2 lenses have no issue with fast shutter speeds and IS on.  It works for me so I leave it on but your mileage may vary (especially depending on the lens).   

[Skulker]

I used to find some lens extender combination would be better with IS turned off when I had my 7D.

But normally I leave it on all the time and don't seem to have a problem.