Comparing Lenses: Kit versus Canon 24-85 USM

[Chazs]

This evening I spent 2 hours and 100 pictures comparing my kit lens (DRebel) with aCanon 24-85 USM lens, suspecting I have a faulty 24-85. After taking identical photos throughout the full range of both lenses (f-stops and zooms), it is VERY apparent that the kit lens, by far, focuses incredibly sharper than the 24-85. Even with a small aperture on the 24-85, the focusing is not as sharp as wide open on the kit lens. Also, the 24-85 shows some front focusing (front focusing must be a lens phenomena and not a camera phenomena as I originally thought).

Does this scenario sound possible? I have a new 24-85 on order that I'll trade my current one with in hopes I have a goofy one.

But for those with more experience with Canon lenses, shouldn't the 24-85 be better than the kit lens? For now, I guess I'll stick with the plastic kit lens. :(

[Olegis]

If the lens front-focuses, then it will be very hard to get decent sharp images with it while in auto-focus mode. You can try to determine whether your camera / lens combination focuses well - with this test (http://www.photo.net/learn/focustest/) for example.

[Tom W]

Yes, it sounds like that 24-85 might be a dud. Since you've already got a replacement coming, you can re-run your test. It should be a good lens. Then again, I bought one used and it had some softness issues - I sold it off to a broker the next day.

Also, see this thread about testing lenses - Atkins' test at Photo.net is OK, but there's a lot of opportunity to mess it up.

http://www.photography-on-the.net/forum/showthread.php?t=32810

There's a link in there where Pekka shows a good test setup as well.

[DaveG]

This evening I spent 2 hours and 100 pictures comparing my kit lens (DRebel) with aCanon 24-85 USM lens, suspecting I have a faulty 24-85. After taking identical photos throughout the full range of both lenses (f-stops and zooms), it is VERY apparent that the kit lens, by far, focuses incredibly sharper than the 24-85. Even with a small aperture on the 24-85, the focusing is not as sharp as wide open on the kit lens. Also, the 24-85 shows some front focusing (front focusing must be a lens phenomena and not a camera phenomena as I originally thought).

Does this scenario sound possible? I have a new 24-85 on order that I'll trade my current one with in hopes I have a goofy one.

But for those with more experience with Canon lenses, shouldn't the 24-85 be better than the kit lens? For now, I guess I'll stick with the plastic kit lens. :(

I've got a 24-85. It was my first Canon lens and mine compares favourably with my L series lenses in sharpness, if not in speed. Perhaps you do have a bad one.

By the way the kit lens with its smaller image circle could be sharper than any zoom lens designed for 24x36 film/sensor sizes. If you check the specs you'll find that 35 mm lenses resolve with much higher numbers than medium format lenses, which are, in turn still much better than large format lenses.

To make a larger image circle seems to requires a trade off of fewer lines of resolution per mm. What makes the medium format images better than 35mm, (and large format images better than MF) is that the size of the negative more than makes up for the inferior lens resolution.

Now with the kit lens it's doubtful that Canon has gone to much trouble to make the resolution higher than they have too. But they could in an "L" series lens with 1.6 conversion. I just hope that they don't and in another three years 12 MP full frame DSLR's will be available from Canon at 10D prices. Hey in 2001 there was a Canon 6MP camera sold with half the specs of a 10D and it was yours foronly $22,000 US! So don't laugh too loudly.