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05/13/2008 10:19:13 PM · #1 |
| I have a 400mm with two 2X extensions tubes (1600mm) set up out back to get a picture of the moon, but it will not focus at all with my 5D. When I try to focus it just goes back and forth like it has nothing to focus on. I tried to focus on some birds on a telephone pole but the same thing happened. Anyone know what's going on? |
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05/13/2008 10:21:15 PM · #2 |
| maybe the its not wired to go through 2 teleconverters... thats why canon put manual focusing on the lens... have fun :) and good luck with your shots... please post them |
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05/13/2008 10:26:50 PM · #3 |
| With two 2x converters you lose 4 stops, so your max aperture becomes f/11. The 5D will only AF up to f5.6. Try one teleconverter, it should work. FWIW, you will probably get as much resolution at 800mm as you will at 1600mm, given additional image degradation from the second converter. |
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05/13/2008 10:28:13 PM · #4 |
Don't some of the extension tubes available steal some of the light, like 2 stops worth? If so, it is possible the AF sensor is not getting enough light in order to focus. You should try focusing on something very brightly lit. However it could be the connections also.
Edit: Damn, beaten to the punch.
Message edited by author 2008-05-13 22:28:41. |
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05/13/2008 10:42:13 PM · #5 |
I just gotta say ... I'm jealous!!! Canon 400mm f/2.8L IS
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05/14/2008 02:15:29 AM · #6 |
Thanks for everyone's tips. Apparently you're right in saying that it isn't meant for 2 converters, because in the metadata it only says 800mm when it was 1600. I'll post some photos later, but it sure was close-up to that moon!
Message edited by author 2008-05-14 02:15:53. |
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