Alley in Pisa, Italy

by Lars Kotthoff

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I have the setup that is shown in this figure. The view is from the top. I have a beam splitter which splits the light that is collected from a SLR lens. To be able to focus the light I have a diverging lens in front of the slr lens. I lose a lot of light with this setup. Are there any other options I have for focusing the light? Maybe a relay lens or some type of transfer optics? I don't want to reinvent the wheel. Thanks

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Try uploading the image to imgur.com then posting the link –  thomasrutter Mar 10 '11 at 1:13
    
Thank you. Here is a link to the set up imgur.com/FaAJZ –  JMD Mar 10 '11 at 1:16
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I'm not sure how this relates to photography. This is probably better suited for a physics or applied optics forum. –  Alan Mar 10 '11 at 21:29
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That is an interesting setup. Can you tell us why you need to do this? Understanding the problem might help one of our community to suggest an answer. –  labnut Mar 11 '11 at 7:27

1 Answer 1

The problem is that placing the beam splitter between the lens and the cameras increases the distance between the lens and the sensor to the point where you can focus only at very close distances.

One solution is to buy a lens for a large-format or viewfinder camera: these are designed for greater lens-to-focal plane distances and many of them have largish maximum apertures. There's a good market in secondhand lenses. See Ken Rockwell's article for a start. The Ebony site has a good discussion of lens extension and points out that retrotelephoto lenses can be used to get greater extension (than their nominal focal lengths indicate).

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Thanks for the info. I was not aware of large format cameras. –  JMD Apr 16 '11 at 15:34
    
@JMD There are other lenses around, too, that might work well and be cheap, depending on the quality you need. Look at enlarger lenses and lenses from projectors (such as old slide projectors). –  whuber Apr 16 '11 at 17:05

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