Parfocal, EOS40D and Lenses

[Roger Rosales]

Hey guys,

I'm back again with some questions. I've come across some more issues at work with our Canon 40D camera . OUr lens, Ultrasonic 28-135mm has a VERY soft focus to it. We're shooting at full wide and the edges of certain portions of the products come out blurred.

Also, the fact that this lens is not parfocal makes it difficult to focus the larger items.

My questions is, is it normal for this lens to have a soft focus to it? Or am I going to need to send it in to Canon for repair?

We're also looking into buying a better lens for the camera and parfocal feature is a definite must. Which is a good lens that takes very sharp images? I can probably deal with it if it's not parfocal, I would just really perfer it. I noticed Tamron lenses are really good. We used a fellow co-workers tamron film lens with the 40D amd took superior photos.

I tried attaching a full res. image but the resolution is way too big. 3888 x 2592

Any thoughts or ideas?

[Daniel Browning]

Originally Posted by Roger Rosales

We're shooting at full wide and the edges of certain portions of the products come out blurred.

Are you sure that the edges are within the depth of field?

Originally Posted by Roger Rosales

My questions is, is it normal for this lens to have a soft focus to it?

It depends on your standards. Look at this 28mm f/4 comparison with the much more expensive EF 24-105 f/4 L (mouse over to compare).

Originally Posted by Roger Rosales

Which is a good lens that takes very sharp images?

Canon EF-S 17-55 f/2.8 IS. The cheaper Tamron 17-50 f/2.8 and Sigma 18-50 f/2.8 also have excellent resolution (MTF).

[George Kroonder]

If you're using autofocus you could also be experiencing a problem with backfocus. Esp. when you're using longer focal lengths. Try if you can focus better manually.

The D300 lets me input offsets for backfocus adjustments for lenses, but I don't think the D40 can accommodate those.

George/