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Old Jul 7, 2009, 7:57 PM   #1
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Default Canon EF 20-700mm 4L IS USM

I have had this lens for couple of years and haven't used it a lot. Lately I took some pictures of the hawk with a blue sky in the background and I noticed dark spots in several places (I counted at least 6+ dark spots in some pictures). I thought the problem was some dust particles on the lens. I cleaned the lens and the problem persisted. Is anyone familiar with this kind of lens problem? I am attaching the picture to illustrate the problem. Thanks in advance for any feedback. I just hope I did not buy a "lemon lens".


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Old Jul 7, 2009, 8:05 PM   #2
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I'm 99% sure that this will be dust on the sensor and nothing at all to do with the lens so clean that (air blower is the best way) and you should be fine.
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Old Jul 7, 2009, 8:09 PM   #3
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Thank you! Will try that!
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Old Jul 7, 2009, 8:11 PM   #4
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You're welcome.
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Old Jul 8, 2009, 10:07 AM   #5
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Mark, I was very excited with the idea of using an air blower to clean the sensor. This morning I took a few pictures and unfortunately the problem did not go away. I went back to my pictures and examined pictures taken with different lenses. To my surprise I found out that the EF100mm lens produced the same dark spots. I went a year back (7/2008). The images taken with different lenses were starting to show the problem a year ago. No images up to 7/2008 show any darks dots in them. So, I believe it's Canon 20D that is causing the problem. Do you still think it's the sensor or something else that is causing the problem?
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Old Jul 8, 2009, 10:12 AM   #6
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Yes pretty sure it is still that. Some dirt is really stubborn. A good test is to shoot the sky and use different apertures, you should find that the narrower the aperture the more defined the spots are.

You can get special swabs to clean the sensor, I've never used any of these options and not sure I would on my more expensive kit. You can also get it cleaned by Canon service.

Quite often you can see the dirt on the sensor so take a good look.
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Old Jul 8, 2009, 10:15 AM   #7
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Yep. That looks like dust. For stubborn dust, blowing alone may not remove it. Here's a site that goes into a lot of different sensor cleaning methods available (for example, Sensor Swabs with Eclipse, Sensor Cleaning brushes and more).

http://www.cleaningdigitalcameras.com/index.html
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Old Jul 8, 2009, 10:18 AM   #8
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Thanks again Mark! You are right , it must be the sensor causing the problem. I'll try to look at it closer.
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Old Jul 8, 2009, 10:20 AM   #9
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Thank you Jim for the link! I'll look at it!
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Old Jul 13, 2009, 2:41 PM   #10
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Which lens is this? I am pretty sure Canon (or anyone else) makes a 20-700mm lens.
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