My 15-85 IS: Still Off? Or is this expected performance?

Well, as I wait for my 50mm 1.4 to return from Canon due to a bizarre flare issue some of you may have read about, I now turn my attention toward the 15-85 lens. (I had recently sent it in for service due to rather poor corner sharpness, noticeable even when the lens was stopped down.)

The good news is that it *has* improved. However, some of me still thinks it may be a bit off, especially when folks have claimed this lens *can* be sharp corner to corner wide-open.

Here's an example image taken at 15mm f/3.5. Note that this was shot in RAW and posted onto the forum. I've done no editing to it and have left Adobe Camera Raw at all default settings. Also, all of these 100% crops were taken from the very edge of the frame.

Full View
(Oh yeah, another brick wall. I'm almost excited...)

Wide angle zooms tend to be weak at the edges. That doesn't look too bad for corner sharpness. Nudge the clarity up to about 25 and push the sharpness to about 45 with a mask of about 10-15. I bet it will tighten up quite a bit. You could also see if that lens is supported by the new Digital Lighting Optimization software in the latest version of DPP. If it is run it through there and compare results.

Scatterbrained wrote in post #14824156
Wide angle zooms tend to be weak at the edges. That doesn't look too bad for corner sharpness. Nudge the clarity up to about 25 and push the sharpness to about 45 with a mask of about 10-15. I bet it will tighten up quite a bit. You could also see if that lens is supported by the new Digital Lighting Optimization software in the latest version of DPP. If it is run it through there and compare results.

I should add that stopping down does help. Here's an example of that:

15mm f/8
100% Crops. (These were also taken from the extreme edges of the frame, except for the center image.)

*Center*

HTTP response: 404 | MIME changed to 'text/html' | Byte size: ZERO

A) that's some low contrast lighting, which will remove the definition from the subject making it appear less sharp.
B) I'm assuming there is no filter on the lens? If there is remove it and reshoot. Either way I wouldn't expect that lens to have super sharp corners at 15mm. My 24-70L isn't too sharp in the corners at 24mm either.

Scatterbrained wrote in post #14824399
A) that's some low contrast lighting, which will remove the definition from the subject making it appear less sharp.
B) I'm assuming there is no filter on the lens? If there is remove it and reshoot. Either way I wouldn't expect that lens to have super sharp corners at 15mm. My 24-70L isn't too sharp in the corners at 24mm either.

There is no filter attached, and yes, the lighting is a bit flat. My apologies.

(The natural vignette of this lens at 15mm isn't helping either.)

The natural slight curvature of the focal plane and the equally natural fall off in performance explains the weakness at the extreme corners at f/3.5. You have shown how it improves at f/8, but what about f/16 and up?

All I'm seeing is entirely normal.

You have to expect that with zoom lenses

Ive had two copies of this lens and i would say the same as the others, its to be expected at 15mm wide open.

Unless shooting brick walls is really your thing, I wouldn't worry about it in normal life

artyman wrote in post #14824913
Unless shooting brick walls is really your thing, I wouldn't worry about it in normal life

+1, not seeing anything of concern considering it's wide open at 15mm.

Thanks guys for the quick responses.

How about my f/8 pictures? Anything of note there?

I guess all is well? Is that what I am to assume?

To be 100% honest: I'm actually looking to sell this lens, as I really want to upgrade my 70-300 IS USM to either a 300mm f/4 L or a 70-300 L. That leap in performance would be far more useful than the jump I made from my old 18-55 IS kit lens to the 15-85, when I rarely shoot at a wide-angle anyway.

I just wanted to confirm that it is functioning properly so I don't rip somebody off with a dud. I do not want to be "that" guy...

That looks normal to me. The fact that all the corners look quite similar in performance would also indicate that there is no decentering (of significance).

That fact that you don't find the leap in performance from the 18-55 to 15-85 all that great is not because your 15-85 has trouble, but that the 18-55 is a surprisingly good lens in the IQ department for the money.

TheRightLight wrote in post #14824146
Well, as I wait for my 50mm 1.4 to return from Canon due to a bizarre flare issue some of you may have read about, I now turn my attention toward the 15-85 lens. (I had recently sent it in for service due to rather poor corner sharpness, noticeable even when the lens was stopped down.)

The good news is that it *has* improved. However, some of me still thinks it may be a bit off, especially when folks have claimed this lens *can* be sharp corner to corner wide-open.

Here's an example image taken at 15mm f/3.5. Note that this was shot in RAW and posted onto the forum. I've done no editing to it and have left Adobe Camera Raw at all default settings. Also, all of these 100% crops were taken from the very edge of the frame.

Full View
(Oh yeah, another brick wall. I'm almost excited...)

Center Crop

Upper Left Hand Corner

Lower Left Hand Corner

Upper Right Hand Corner

Lower Right Hand Corner

Perhaps the proximity to the wall is part of the equation. According to EXIF data you were only 6 feet away. try taking "real" picture and see what happens.