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Old Jan 16, 2006, 8:54 AM   #1
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I tested BULB mode last night when shootingy the sk. I have tested BULB for 120 seconds, 200 seconds and 360 seconds on all ISO range from 100...till 1600. I found that there is something similiar to dust on CMOS sensor on the photo. Some black spot noticeable on most of the photo with exact position on the photo. I wonder if this is dust on CMOS, Lens or CMOS malfunction problem..... But when I shoot in normal shutter, the spot doesn't exist... It only exist when I shoot BULB mode ....
FYI, I using Canon EOS 350D with 18 - 55mm Kit Lens..

Here are some of the photo I manage to post it..
1. This is the photo where I notice some black spot (F22, 361s, ISO400)

2. 100% Crop...

3. Another 100% Crop

4. The rest of long exposure photo where the black spot is noticeable

a. (F22, 25s, ISO400)

b. (F22, 361s, ISO400)

c. (F22, 100s, ISO400)

d. (F16, 25s, ISO800)

e. (F22, 30s, ISO1600)

f. (F22, 30s, ISO1600)

Anyone know what happened? what are the root cause? Is this normal?..
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Old Jan 16, 2006, 9:49 AM   #2
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It is difficult to say if its dust on the sensor or the lens. But I believe at least the lower and right side marks are dust.

If you have a blower ball (one without the brush, you just want to blow dry, non-cooled air. And *DO NOT* use compressed air) use that to blow off the lens (both back and front) and the sensor. Try it again.

A good way to tell if its dust is to photograph a light colored wall at a lower ISO. If its very big, it will show up even then and with a white background be really easy to see.

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Old Jan 16, 2006, 10:00 AM   #3
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Looks like dust to me.

Keep in mind that the smaller the aperture the worse it will look.

Also keep in mind that you should probably avoid f22 and f16 on the XT if you can for dfifraction reasons.

Use them if you need them, but you should get sufficient DOF from f11 or f14 for most purposes.
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Old Jan 17, 2006, 4:59 PM   #4
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All the pics look like dust except #2, which is undoubtedly a UFO... :?

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Old Jan 17, 2006, 5:28 PM   #5
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to find out if it is dust for sure. with a wide angle lens on stopped down to around f/8. fill your frame with a white sheet of paper and take the shot. dump it into photo shop or elements and go to auto levels. if there is dust there it will show up right away. Then go to your camera menu and select sensor clean, this will lock the mirror up.(make sure your battery is fully charged.) then with thesensor facing down so the dust doesn't float back down onto your sensor,use a bulb blower as Eric said. Two or three burst of air should do it. then just turn the camera off and your done. Then take another picture of the paper, andtake it back to photoshop.Make sure you clean your lens before you do this. I likea white sheet of paperbetter than a white wallbecause even the texture of the wall will show up in photoshop.If you have some really stubborndust you may have to resort to a sensor swab of some kind.
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