Lens or camera not focused at edges

[Chazs]

I realize this may be a silly question without posting a picture, but...

A few weeks ago I purchased the D Rebel and the Canon 24-85/3.5-4.5 USM lens. It seems that I get quite a bit of "fuzziness" at the left hand side (a little on the right side, too). I know that a lot of lenses show distortion on the edges wide open, but I seem to get it throughout most of the 24-85 range regardless of f-stop. Should a ~$400 Canon lens show an annoying amount of distortion at the edges, or could my sensor in the camera be off a little? Anyone else experience more fuzziness on one side as opposed to the other? It seems that my 20 year old Olympus lenses were far more sharp. Is this Canon's way of telling me I need to mortgage the house and get an L-lens?

[martcol]

Is this Canon's way of telling me I need to mortgage the house and get an L-lens?

I would say, most definately YES!

There are lots of other ways, this is only one of them

Martin[/b]

[robertwgross]

First, you might want to decide if the entire image is unsharp. Most images do require some sharpening to be optimal. However, we don't know the extent of the problem you see.

---Bob Gross---

[DaveG]

I realize this may be a silly question without posting a picture, but...

A few weeks ago I purchased the D Rebel and the Canon 24-85/3.5-4.5 USM lens. It seems that I get quite a bit of "fuzziness" at the left hand side (a little on the right side, too). I know that a lot of lenses show distortion on the edges wide open, but I seem to get it throughout most of the 24-85 range regardless of f-stop. Should a ~$400 Canon lens show an annoying amount of distortion at the edges, or could my sensor in the camera be off a little? Anyone else experience more fuzziness on one side as opposed to the other? It seems that my 20 year old Olympus lenses were far more sharp. Is this Canon's way of telling me I need to mortgage the house and get an L-lens?

I have that same lens and mine has no sign of softness anywhere. In fact it
compares well to my L series lenses. Is this the only lens that you have? If it is
perhaps you should go into a camera store and ask to take a few shots with some
other lenses, including another 24-85.

I think that the problem could be any one of many things and you'll have to do
some tests to see if you can figure it out. It could be a bad lens. It could be a
something on the CMOS sensor. And it could be a "naturally out of focus, but
you think it's a problem", problem.

Select a subject like a brick wall. This will provide corner to corner texture so you
can see sharpness. Put the camera on a tripod a few meters away and keep the
camera as parallel to the wall as you can. Focus it carefully, and fill the frame
with the wall. Shoot a number of shots with different apertures using either
RAW or the "best" jpeg. Try it again with a different zoom focal length.

Now have a look at the results on your computer. The brick wall should leave
no doubt about sharpness on the corners. The tripod ensures that you just
haven't used too slow a shutterspeed and have camera movement blur. The
RAW/best jpeg means that you are using a file size without any possibility of
digital artifacts clouding the results. The varying apertures and focal lengths will
show whether there's a problem wide open or at a specific focal length.

If the lens shows softness as you described after this test and the camera store’s
lenses don't seem to have the same problem, then you might want to see about
returning the 24-85. If the store's lenses share the same problem then it's your
camera. If the test looks OK then you've just had user induced problems like too
slow a shutterspeed, or not enough depth of field.

[Chazs]

DaveG, thanks for all the tips. I'll run several test shots this week. I'll also post a few pictures if it still shows the problem.

[KennyG]

The brick wall test is ideal. It is not unknown for that lens (and a couple of other makes/models) to have a soft corner.

[Tom W]

I would go back to the dealer and get the lens replaced. The 24-85 has a good reputation, but there is the occasional dud. I had one that was soft in the corners - I got rid of it quickly and kept my 28-105 which happens to be an exceptionally good copy.

[robertwgross]

It is not unknown for that lens (and a couple of other makes/models) to have a soft corner.

What would account for that?

---Bob Gross---

[Chazs]

Here is a sample picture that started this discussion. It's not a great picture, but it shows a little of the corner softness. I would expect all the trees on the horizon to have a similar fuzziness. But, I don't think they do. Am I off base here? The total softness disturbs me as well. the camera was set on a ledge, focused at infinity, and I used the 10 second timer to get in the picture.

the original:
http://members.isp01.net/snevetsc/photos/bigshot.jpg

Crops of trees at the left, middle, and right:
http://members.isp01.net/snevetsc/photos/closeups.jpg

I'll work on the controlled focus tests later this week.

CHAZS

[Tom W]

Your pictures do show a softness, particularly in the upper lefthand area. That is similar to what mine did. Did you buy this from a dealer?

Just to be sure, do the brick wall test, and take a couple of shots with high-contrast detail across the viewing area, but of relatively equal distance from the camera so that it is all on the same focus plane.