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Old Apr 1, 2007, 12:44 PM   #1
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Took my Bausch & Lomb 4000 Schmidt Cassegrain Telescope and hooked my K10D up to it just for fun to see how it would work as a camera lens. At 25 yards the DOF was extremely narrow, almost like doing macro work, so focusing on moving birds was interesting at best.

Not the greatest image, but not bad considering the setup!

I used Ben's method to bring out the contrast a bit, since it was a bit flat right out of the camera!





Tom
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Old Apr 1, 2007, 2:32 PM   #2
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Really don't know how to react to this setup ...
did you try some macros :-)

no just kidding, nice experiment - Ronny

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Old Apr 1, 2007, 3:05 PM   #3
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Handheld shot? :lol:

Surprisingly good IQ!

Kjell
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Old Apr 1, 2007, 5:01 PM   #4
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:shock::Oholy s!!! tom. good results but i'd use a monopod

what MM ?

roy
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Old Apr 1, 2007, 6:41 PM   #5
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Good shot Tom and I must admit your 'howitzer' style lens looks less cumbersome than my 'ships gun' style! http://www.stevesforums.com/forums/v...mp;forum_id=80 Scroll down for a couple of pictures.
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Old Apr 1, 2007, 11:10 PM   #6
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Any idea what the effective FL was?
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Old Apr 2, 2007, 5:28 PM   #7
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It is a 1,200mm lens in 35mm terms and the bluebird photo was taken at 1/350 sec and I have no idea what the f/stop was since there is no adjustable aperture in a mirror lens.

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Old Apr 2, 2007, 8:55 PM   #8
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Hi Tom, as far as I know the aperture would be calculated by dividing the focal length by the diameter of the objective lens. I will take a punt and assume the '4000' in the model name indicates a 4" diameter objective which is just a smidgen over 40mm. Aperture then is 1200/40 = f30!

Except your type of mirror has a lesser aperture due to the central obstruction of the secondary mirror, maybe 20% obstructed? I guess an effective aperture of about f35. Does that sound reasonable?
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Old Apr 2, 2007, 10:43 PM   #9
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Hi John, it is 4", so I guess you are correct about the f/stop. The lens is hard to use because of the slow speed, the photo of the Bluebird was 350/sec, which is pretty slow for a 1,200mm lens.

I really only use it as a telescope anyway, but it was fun to try. Here is another photo of the bird without the branch in the way. Not as contrasty as the first one, more like the way it came out of the camera.



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Old Apr 2, 2007, 11:07 PM   #10
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OH Dear! Dunce's cap for me!

Four inches is about 100mm, not 40 like I said!

So thats a nominal aperture ratio of about f1:12 and allowing for the central obstruction an effective aperture of about f1:15.

:? (Boy, I hope I have it right now. :roll




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