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Old Jul 20, 2005, 10:59 PM   #1
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I bought an RebelXT with a EF-S 17-85 IS lens and a EF 75-300 IS lens.

Over all it seems pretty well done, but I was doing some panorama shots and I noticed that I couldn't seem to match brightness levels even when taken on manual.

So I took a 20x30 "grey" board and shot 17,50,85 and 75,300 with the two lens with/without UV filter and with/without hoods (Canon hoods).

I was expecting the problem to be the after market UV filters. But not so - it seems the 17-85 has a definite problem. Can someone tell me if me test is wrong or if this is what is expected, etc. For the price I paid, I was expecting better.

Basically the 75 (equiv 120) with UV and Hood looks "ok". No noticeable difference with/without. But if you measure with Photoshop after setting the center to be white, the edges are about 225-230 instead of 255.

But the 17-85 is bad at all settings even without the UV and Hood. I have enclosed a small versions of the a couple of the shots (which were done with RAW and Fine Large).
One at 17 and 1 at 85.
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Old Jul 20, 2005, 11:01 PM   #2
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Here is the 85 end of the lens, again with no UV or hood.
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Old Jul 20, 2005, 11:04 PM   #3
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And one last, the fairly ok 75 (120) end of th 75-300 with UV and Hood
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Old Jul 21, 2005, 5:21 PM   #4
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Ok, I will reply to myself.

What some pretty extensive research, I have found that this is probably "average" quality on a wide-range zoom lens. I was expecting a little better for the price.

The secret is to stop down at least 2 or 3. Problem with that is you are starting at 4.5-5.6 - don't give a lot of room.

I will do some more tests tonight with it stopped down.

Interesting articles:

http://www.fsoft.it/Imaging/Vignetting.htm

http://194.100.88.243/petteri/pont/H...s.html?page=10

Oh, and I just happened to find a package that exceeds even the price of Photoshop:

http://store.dxo.com/login.asp?LID=3

(Don't fall out of your chair)

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Old Jul 21, 2005, 5:30 PM   #5
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One last reply to myself.

At the expense of having this guys site inundated, his is a Photoshop plugin to correct Vignetting. I will be trying it tonight. He will get a donation from me if it works!
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Old Jul 21, 2005, 7:28 PM   #6
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that lens shouldnt vignette though.. i have never used the lens.. but i wouldn't accept that kind of quality.. send it back.. get a new one..
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