Focus Issue anyone Help?

Chaz Photos

Chaz Photos

Jack Elam
Messages
6,282
Name
Chaz
Edit My Images
Yes
I have a focus issue can anyone through any light on my problem
I just got a new Sigma 17-70mm lens and find it not spot on with focus it looks like it is back focusing at first I was going to adjust my camera BUT I tested a kit 18-55 lens and it look
OK so Can you adjust a lens?
Here are two test images
First Kit lens
3675470357_a199a6f094.jpg

Larger copy
3676284922_98a06f1cd7.jpg

Larger Copy
 
shoot some real stuff instead of targets like this that are open to so many problems.
 
Pic 1 is f5.6 with 46mm focal length.
Pic 2 is f4.5 with 70mm focal length.

You are not actually comparing apples with apples here.

Use the same aperture and focal length settings for both lenses then compare depth of field.
 
Chaz Photos said:
...at first I was going to adjust my camera
Click to expand...

How exactly?
I don't believe that the Canon 30D has the microadjustment feature found on the later CANON models. This feature accommodates focus adjustments for up to 20 lenses although the same compensation can be applied to all lenses. That is, the microadjustment feature enables the camera to compensate for an individual lens model if needed. (All this depends on the camera recognising the lens of course which it may not be able to do with non-CANON lenses).

Testing lenses for focus accuracy can be tricky - you need to ensure that you are focusing exactly on the plane where your centre line is placed and that this line is in perfect alignment - not twisted at an angle to the focal plane of your camera which would really throw your assessment out of the window. Also, when testing, you need to test at the widest aperture available and have the target at a distance 50x the lens focal length - according to CANON. (Telephotos are even more difficult to sort out - you need to decide which focal length you will adjust at or else adjust for the average amount of front/back focussing across the range).

I suspect that the best way forward - for your peace of mind at least - is to get your lens checked out and adjusted if needs be. I have recently used H. Lehmann in Stoke who are an approved Canon service centre and offer a lens service for Canon lenses - it may be that they could do the same for a Sigma - you would have to call and check. They charge £30 to check out the lens and if adjustment is needed, will do this for an extra £40, (£70 total). Prices include return postage.

Saying all of this though, I suggest you take some real life shots as others have suggested - of the things you normally photograph, before splashing out any cash.

Alan
 
Unless your camera has focus-correction facility, I'd say you were stuffed - take it back if you're convinced that it's out...
 
I seem to have come up with a similar issue on my 70-200 2.8 HSM1. I'm gonna call down to Jessops tomorrow and get them to sort it. There's a 3 year warranty on UK EX glass according to the Sigma site so I'll see what happens. I'm not that annoyed really, just an inconvienience.

DSC_2675small.jpg
 
You must log in or register to reply here.
Back
Top