FocusScope for Kalart Rangefiner
Description
FocusScope to fit Kalart Rangefinder to make focusing easier. For more information on Kalart rangefinders see [graflex.org](https://graflex.org/speed-graphic/features.html#KalartSide) and [Jo Lommen's site](https://lommen9.home.xs4all.nl/kalartmain/index.html). As designed it takes: - 1.38cm diameter convex lens with focal length 48mm <= f_1 <= 72mm - 1.67 cm diameter concave lens with f_2 = 2 f_1 /3 - the lenses should be placed f_1-f_2 apart The piece with two male threads is the front. The small thread screws into the port on the Kalart Rangefinder. The convex lens is put in the other end and held against the shoulder with a circular spring (I make one from a hairpin) The piece with one female thread is the back. The female thread screws over the larger male thread on front piece. The concave lens goes in the other side and is held against the shoulder with a circular spring. Focus by turning the two pieces with respect to one another. The length of the threaded portion on two cylinders allow the distance between lenses to vary between 16-24mm If you need more focusing distance just change the variables `thread_length_female` and `thread_length_male` (if you change one, I suggest changing the other) If you need to accommodate different lens diameters then you will have to tinker with the inner and outer diameters which will probably involve iteration over a few drafts to get everything to work. If you are in Chicagoland, [American Science and Surplus](https://www.sciplus.com/) is a good place to get suitable lenses. First photo shows an early draft of the scope next to the original Kalart brand product. Second photo is all the pieces to assemble a working scope. The retaining rings are made from a hair pin. Third photo shows the telescope assembled. Last two photos show it on a Graflex Miniature Speed Graphic This design uses Dan Kirshner's OpenSCAD threads module saved as "threads.scad": https://www.thingiverse.com/thing:1938150 https://dkprojects.net/openscad-threads/ It also requires cnt's Knurled Finish OpenSCAD library v2.1 saved as "knurledFinishLib_v2_1.scad" https://www.thingiverse.com/thing:4146258 I found I had to introduce an interior_thread_multiplier to slightly increase the diameter of the interior threads so the pieces would fit together. If your printer is more precise than mine, you may be able to decrease its value for a tighter fit.
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