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David Sekanina

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Posts posted by David Sekanina

  1. Here's a simple relay lens with two achromatic doublets. Left end pics up the image from the focusing screen, right end focuses the image in front of the eyepiece, which then picks it up and magnifies it. In such a setup, you can space the two achromatic doublets further apart, without the relayed image getting out of focus as long as the focusing screen distance stays at the focal point of the first achromatic doublet, and the eyepiece at the focal point of the second achromat.

    images.png.f4078253a7a6fb021249bd5c0f2c6985.png

    I hoped the viewing system on your ACL was as simple as that, but by what you describe, the beams are not collimated in-between. In these more complex cases I bother an optical engineer, which I am not. Sorry I could not help ?

  2. As long as the rays are still collimated in that portion of the viewfinder, so not converging or diverging, this will work. You can try this by pulling out the original viewfinder by a few centimeters while keeping the axis (making the optical path longer) and check if the image stays in focus. If it is still in focus, you're good to go ahead with a prototype. The image is mirrored twice with your add-on, so no image flip.

    You can also use a prism, to ensure the angles meet the close tolerances, or two mirrors, like you said. Enhanced Aluminum or enhanced Silver mirrors have an extremely high reflectivity, the light loss will be minimal.

     

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  3. Horses for courses. Some amazing films were shot on BLs, so I'd consider it, if the rental is significantly cheaper - or even buy one. Alan Gordon sold a 2perf BL two years ago for around 14K.

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