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Photo Forum / Digital Photography / DSLR Cameras / November 2005Odd dots on Canon 10D
No, it's not what you think. I was shooting panoramas at the Grand Canyon, entailing rather rapid shooting. On some of the pictures, there are dark dots that look, for all the world, like dust on the sensor. The odd thing is, they're not present for later shots, and then they recur. I'm wondering if it might not be the cold -- it was about 25 degree fahrenheit when I was shooting. Now I'm in warmer climes and they appear to have vanished again. Has anyone ever seen anything like this? > No, it's not what you think. > [quoted text clipped - 6 lines] > > Has anyone ever seen anything like this? Did you have a deeper DOF eg f22 than usual ? > No, it's not what you think. > [quoted text clipped - 10 lines] > > Has anyone ever seen anything like this? It might be dust on the lens as opposed to the sensor, dirt there will render either sharp, out of focus, or not visible depending on what apeture you use. You can either a) clean the lens and hope that fixes the problem or b) take shots of a clear sky or similar light tone subject at the widest apeture and again at a narrow apeture (f22 should do it). If the spots appear on the f22 shots it is dust on the lens.  SignatureUsing Opera's revolutionary e-mail client: http://www.opera.com/mail/ According to Kelly B <boomboom4@cox.net>: > > No, it's not what you think. > > [quoted text clipped - 14 lines] > render either sharp, out of focus, or not visible depending on what > apeture you use. Dust on the lens should be pretty much invisible except at the absolutely tiniest aperture -- f/64 or so (which most lenses don't even offer) -- and even then, it should form quite large blobs, not the relatively tiny ones found with sensor dust. Dust on the sensor, however, can be quite small, and it will only appear at small apertures, because it is not *really* on the sensor, but on top of the anti-aliasing filter and the IR-blocking filter which cover the sensor. A tiny aperture produces a very narrow cone of light which casts a shadow on the sensor. A larger aperture produces a wider cone, most of which misses the dust. This results in an often undetectable darkening of an area around the dust particle. > You can either a) clean the lens and hope that fixes the > problem or b) take shots of a clear sky or similar light tone subject at > the widest apeture and again at a narrow apeture (f22 should do it). If > the spots appear on the f22 shots it is dust on the lens. At f/22 it *should* be dust on the sensor, not on the lens. Enjoy, DoN. SignatureEmail: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- > It might be dust on the lens as opposed to the sensor, dirt there will >render either sharp, out of focus, or not visible depending on what >apeture you use. You can either a) clean the lens and hope that fixes the >problem or b) take shots of a clear sky or similar light tone subject at >the widest apeture and again at a narrow apeture (f22 should do it). If >the spots appear on the f22 shots it is dust on the lens. Dust in the lens almost never shows up in an image as anything but a slight loss of contrast. Sensor dust varies in visibility with aperture, *quite* dramatically. Signature<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<> John P Sheehy <JPS@no.komm> ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>>< > Sensor dust varies in visibility with aperture, *quite* dramatically. My f/170 body-cap pinhole lens shows it up quite dramatically. One of these days I have to try cleaning my sensor so I can start using that lens. SignatureBen You buttered your bread, now lie in it. >>Sensor dust varies in visibility with aperture, *quite* dramatically. > > My f/170 body-cap pinhole lens shows it up quite dramatically. One of > these days I have to try cleaning my sensor so I can start using that > lens. Hmmm, I haven't used my pinhole body-cap in ages. I'll have to pull it and have a look see. ATM at f/22 I can see 6 dust spots. Greg > No, it's not what you think. > [quoted text clipped - 6 lines] > > Has anyone ever seen anything like this? Hi PTRAVEL, You were using a panorama type lens? Really wide angle, out in the desert air? South rim, on a bright sunny day? I have had similar spots with a fisheye lens, on bright sunny days. They are called sun spots. They happen in both 35mm and digital. They only thing you can do is try to shade the lens with something. Then you BLH. The only problem with this is you sometimes get a photos of what you are shading the lens with. To get a photo with out a sunspot out on the ocean of a sundog, I think I shot 20 shots one day. My wife looked at them on the laptop and said why. I said to get rid of the sunspots. She just looked at me and said what are you talking about? Then I pointed out a sunspot in the photos... roland |
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