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Old Jan 23, 2006, 12:29 AM   #1
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I recently got a 70-200 f/4 L, and have generally been very pleased with it. Today, though, I noticed what I believe to be a defect. I have not used the lens heavily at 200mm with scenes where everything is at infinity. As a result, I didn't notice the softeness in the left side of the frame. Today, when looking at this picture at 100%, I noticed that the extreme left side is much softer than the rest of the frame, including the extreme right side.

Here's the full photo, resampled and with some unsharp mask applied. Even here, the left side appears just slightly soft...

I'm well aware that it's not a great picture, so please don't point that out:roll: (although I admit that many of the pictures people use to point out supposed equipment problems are in fact lousy pictures in the first place)

Here are the pertinent EXIF fields:

Model - Canon EOS 20D
ExposureTime - 1/640 seconds
FNumber - 5.60
ExposureProgram - Aperture priority
ISOSpeedRatings - 100
ExposureBiasValue - 0.00
FocalLength - 200 mm
Focus mode - AI Focus
Metering mode - Center weighted

From the full-size photo with no post-processing, I cropped a 3504x500 strip through the middle of the frame. I then cropped out the extreme left and right sides of this:

The right side is clearly sharper. Compare the detail in the palm trees and the street lights (the street lights in the left side are so blurry that they are hard to even locate).

It can't be a depth-of-field issue, since the scene was at infinity. It can't be camera shake, because most of the photo is sharp (and 1/640 at 200mm should eliminate shake, especially since I was bracing on a railing).

The lens is, as I said, quite new, and Canon's service center in Irvine is a short drive away. Should I take the lens in for service?
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Old Jan 23, 2006, 9:46 PM   #2
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Maybe shoot the same shot on the left and right side of the lens, so you can compare apples to apples (ie two shots).

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Old Jan 24, 2006, 10:58 PM   #3
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That's a good idea. I'm fairly positive an element is out of allignment, but a more conclusive test would be useful in convincing others (namely, Canon service) that the lens is defective.

Here's something else I'm wondering about... the deadline for mailing in the rebates is coming up soon, and I haven't sent it in. Should I go ahead and send in the rebate now, even though I know I'm taking the lens in for service (and will possibly have to get a new one)? I'm taking it in to the service center on Friday (the only day of the week when I have free time during its hours of operation).
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