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UltravioletPhotography

Need help with finding a large format lens for SWIR


Andy Perrin

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So I recently acquired (for 12% of the original price...) a 1550nm Converter for CCD Cameras, which uses up-conversion with phosphors to move the 1550nm band into the NIR (950nm) part of the spectrum so it can be imaged with ordinary cameras. The tube apparently goes between the camera body and the lens. The lens must be large format (>28mm image circle) and have a 42mm mount. So I need help lens shopping.

 

Here are the specs of the tube:

post-94-0-42471300-1477075305.jpg

 

How does this B&L 8x10 TESSAR 1c large format lens look? Is it known what the threads are and what the mount is?

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Are you actually asking about a kind of relay system? What kind of image circle is projected from your device? (skip that, i see from the table we're dealing with C-mount optics).

 

You probably need something that can deliver 2-4 X magnification depending on the size of the final frame. Perhaps a reversed 28 mm lens could do?

 

Anyway, true large-format lenses have long focal lengths and probably would be very awkward to implement as an optical "in between" component.

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Correct me if I'm wrong - but a 28mm image circle is tiny, you don't need a large format lens. A large format lens can throw an image circle of 14" or so if it's intended for 10x8 (depends on the lens) and M42 is made mainly for 35mm cameras - so surely a half decent M42 lens second hand will do a good job? If I'm missing something here then point it out
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At this point you know everything I know. But the lens goes on the end, the tube goes in the middle, so I don't think the lens is an "in between" component? I have several M42 lenses but they are not large format. It definitely specifies large format in the specs. Don't ask me to explain how that is compatible with a ">28mm image circle." Maybe it's the ">" that's relevant there. The tube is 9.7cm long, so that may have something to do with all this?

 

Unfortunately I have not been able to find documentation yet, and the tube is in the mail still. I'm not buying anything else till it arrives and I can see whatever there is to see. (There may be some additional docs with the tube.)

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In Edmund Optics own terminology, large format lenses start with image circle of 43.3 mm, which is equivalent to 35mm format, see these links:

 

http://www.edmundoptics.com/imaging-lenses/fixed-focal-length-lenses/lf-series-lenses/85199/

http://www.edmundoptics.com/imaging-lenses/fixed-focal-length-lenses/lf-series-lenses/85203/

http://www.edmundoptics.com/imaging-lenses/fixed-focal-length-lenses/lf-series-lenses/85204/

 

It is clearly stated in the specifications posted in the first post: "Large format (>28mm image circle).

 

So your regular M42 lenses should work as long as they transmit in the required range.

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Ah hah, thank you, Alex! I did not realize that Edmund Optics had their own terminology for these things (so I didn't try to look it up).
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