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Old Sep 2, 2005, 9:39 AM   #1
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Hi everyone! I'm new to the world of digital SLR photography (I just got the Rebel XT) and am so excited to be a part of it. Yesterday my new Canon 70-200 4L arrived and I went to the local soccer field to try it out - WOW! The photos are beautiful and I didn't even try. :-)

My new Canon 17-85 lens, however, is showing a LOT of Chromatic Aberration - enough where I can see it in an 8x10 print. We're going to Japan next month and I was hoping to just take this lens, but I'm not convinced of its quality. I've attached a photo that shows examples. Can anyone with this lens tell me if this amount of CA is normal, or if I have a bad lens?

I'm debating if I want to trade it in for a 17-40, but I'm not sure I want to lose the range. Help? Advice? Comments? Thanks in advance!
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Old Sep 2, 2005, 9:58 AM   #2
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Here is another example... obviously it wasn't meant to be a pretty picture... but you can very clearly see the color fringing against the light fixture at 100%.
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Old Sep 2, 2005, 11:24 AM   #3
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Fairly normal for this lens. Not uncommon to the 24-70L, 85 f1.8, among others. Go and enjoy the lens.
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Old Sep 2, 2005, 11:11 PM   #4
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It sounds "normal" to me. The 17-40 f/4 L is also not free of this problem, particularly towards the edges. The 18-55's performance is significantly worse in this regard.Phew

Can't say how the 17-40 and 17-85 compare in this regard personally, but I have heard that the 17-85 is worse. I find the range of the 17-40 to be very good (equivalent full frame FoV would be 27-64, which is a "classic" range, encompassing 3 common primes - 28, 35, 50). I fill in the gap between 40 and 70 with a 50 1.8, but sadly don't do often enough considering how good the 50 is.

The 17-40 is weaker towards 40 though, and if you're pushing that side regularly (I push 17 more often), the 17-85 might be better, but I haven't seen anything conclusive on this.


Alternatively, you might be able to Photoshop out the one that really bother you.
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Old Sep 3, 2005, 3:25 AM   #5
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I'm generally quite skeptical of differences in copies of lenses, but this looks worse than mine.

Are you using a filter on the lens by any chance? If you are then I would strongly suggest trying the experiment with the filter on and off. I bought two expensive Hoya Pro UV filters to protect my lenses and then realised that even though they were the best Hoya made they had quite noticable adverse effects on the photos. I also realised that I've never actually scratched a lens filter - even when not using hoods, now I do use hoods I have left my filters in a drawer somewhere.

Assuming you're NOT using a filter on the lens however....

I would expect the 17-40 to be somewhat better, but the wider the angle the harder it gets to manage CA in lens design - this is obviously one of the real disadvantages of cropped digital sensor compared to FF. You need shorter focal lengths to get the same FOV.

The solution however is much cheaper than buying the 17-40 and losing the range & IS.

You can buy a software upgrade for your lenses...

http://www.dxopro.com/

It's basically an excellent corrector of all kinds of distortion as calculated specifically for your camera and lens combination, and is also a very good RAW converter. Perhaps not quite up to CameraOne or suchlike, but excellent at recovering blown highlights and reducing shadow noise.

I don't use it for sharpening, but since purchasing this my average time in PS per picture has dropped quite dramatically. Before DXO I used to adjust levels, contrast, CA, vignetting, etc. on all my "keepers". With DXO I sharpen in PS but don't have to do anything else 90% of the time, and if all you do for sharpening is apply a single USM then you might as well do it in DXO too.

The only annoyance is that Canon has stopped writing the distance info into the Exif data for the shot, probably precisely because it allows companies like DXO to turn the results from a mid-level lens into the equivalent or better than you would expect from much more expensive lenses. So this means that to correct certain types of distortion and lateral CA you need to tell the program what the focus distance was, on the 17-85 they only ask you to put it within 3 ranges 0-1m, 1-3m, 3m+ so it's not difficult to do just by looking at the photo.

Of course they sell lens modules for the L lenses too, so they get better too, but the manufacturers don't like the fact that it can be very hard to tell the difference between mid and high level lenses after both have been through the DXO process.

DXO have a trial version - so there's nothing to lose by checking it out. I tried v2.0 and wasn't quite impressed enough to buy it, but recently purchased v3.0 because they added a raft of extra features which made a real difference, plus I was waiting for them to add the lens module for the 70-300 DO on the 20D.

Here's the LL review, which I think is quite balanced.

http://www.luminous-landscape.com/re...tics-pro.shtml

If you do decide to download the trial version I would be very interested in seeing a
before and after picture of the sample you have posted above.


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Old Sep 4, 2005, 12:32 PM   #6
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"The only annoyance is that Canon has stopped writing the distance info into the Exif data for the shot..."

I wonder if there is a firmware hack that adds it back in, but then again I'm still kind of leary about firmware hacks.

Oh yeah one more question, what color space does Dxo support? Does it support Prophoto?
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Old Sep 4, 2005, 2:54 PM   #7
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Colour spaces:

sRGB
Adobe RGB

Any other custom ICC - but you need a custom ICC file.
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Old Sep 6, 2005, 1:16 PM   #8
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Thanks for the info! I've been away for the past few days but will look into this software. I wonder if it's available for macs...

No, I did not have any filters on this lens.

FYI, I returned the lens to B&H and have asked for a replacement - we'll see if the next is any better.
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