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Old Dec 24, 2004, 6:34 PM   #1
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I've been trying to use the digital Rebel with a Canon 100-300 lens to shoot bats on cave ceilings. The lens is pointed straight up and the motor moves the lens very sluggishly or not at all. Typical temperatures are in the 32-42 F range (0-6 C).

Is this a battery issue, exacerbated by the cold? Any suggestions {other than manual focus, of course)as to what I can do ?
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Old Dec 24, 2004, 9:44 PM   #2
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Does it behave this way inside in reasonable tempratures?

I wouldn't expect it to work very well (AF needs contrast to work and in the dark pointing at the sky there isn't much contrast), but that should show its self by hunting... not by moving "sluggishly or not at all."

It could be the cold.

Eric
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Old Dec 24, 2004, 10:11 PM   #3
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The camera and lens behave normally at room temperatures when shooting horizontally. As for the required contrast, we use a laser pointer to project a figure on the ceiling that the AF can lock on. This, too, works fine in more normal circumstances, even in a dark room when focusing on a blank wall.
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Old Dec 25, 2004, 3:27 AM   #4
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Just to throw my 2 cents in, a couple days ago I was out shooting with my
100-400L IS USM with my Drebel. The temperature during the shoot ranged from 5F to
10F. I was shooting mainly birds, therefor I was shooting at all angles
including straight up. Had no autofocus problems. The focusing speed
seemed pretty much normal. It was a bright sunny day though.
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Old Dec 25, 2004, 8:40 AM   #5
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That does sound weird to me. Does it always behave this way, even right after you bring it out side? You could leave the battery in your pocket, so it stays warm. Then setup the camera and just before you take a picture (just a test shot) put the battery in and take the picture. That should eliminate the cold battery idea.

It does seem like something is wrong (defective) but I have a hard time seeing how the vertical position would cause a problem.

Eric
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Old Dec 25, 2004, 9:05 AM   #6
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One of the guy's on our crew thought shooting vertically might be related to the problem under the theory that the motor has to work harder to push the lens straight up. Woodmeister's experience sounds like an even more severe test (larger lens, colder temps), though.

I should have mentioned that we experienced the same problem when using that lens with an EOS 3 film camera.

Sounds like some experimentation is in order. At the next opportunity I'll try a different but similar lens and play around with keeping the battery and lens warm.
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Old Dec 29, 2004, 2:32 PM   #7
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Follow up: It turns out the lens is faulty. When compared with a new one right out of the box, the old lens takes about 3-4 times as long to focus and makes a bit of noise while doing it. In the cold the problem is worse. The tech at my photo shop thinks the mechanism is jammed with dust from the harsh cave environment the lens has been exposed to. Unfortunately, he also says that repair is not economical.

It was only used about 5-6 times, but Iguess this lens, a Canon EF 75-300 II USM, is not suitable for the application. :sad:Unfortunately, my department's budgetcannot afford L-series glass (and who knows whether that would bemore durableanyway?)

Thanks to those who commented.
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