The magnifying loupe allows the user to view the screen of a digital camera (or any flat object) at a closer distance than normal and thus the image looks larger so more detail can be seen.
The openSCAD program generates stl files for a number of pieces which when assembled with a lens completes the loupe.
When the loupe is to be used with a digital camera, it generates stl files for four pieces. The sizes of the pieces depends upon the screen size specified, the lens diameter, thickness, and focal length, and the length of the bracket to attach the loupe to the camera tripod socket. If one doesn’t want to attach the loupe to a camera, but just use it as a magnifier, then you don't need to print the bracket
For my prototype loupe I used a 19x67 meniscus lens that I had purchased from Edmund Optics. The first number is the diameter in mm and the second number is the focal length, also in mm. In order to get a sharp image in the corners, one should use a lens whose focal length is greater than the diagonal measurement of the screen. The diameter of the lens will determine the field of view that one can see at one time. It is good to make this larger than 18mm.
The second version of the loupe used a 30.7x78 PCX (plano convex) lens for a screen size 2.2 x 3 in. The larger lens and longer focal length made this version easier to use. This lens is currently available from Edmund Optics at a low price in the clearance section of the website. It is part number 20518.
The bracket has a slot to allow some adjustment in the loupe position. The slot and the hole in the pyramid of the loupe are sized for an 8-32 machine screw. It also has a large hole to allow a 1/4-20 screw to attach to the tripod socket. The middle sized hole in the thicker part of the bracket can be tapped for a 1/4-20 thread to allow the camera with attached loupe to be mounted on a tripod. If you are careful you should be able to cut threads in the plastic. I usually carefully enlarge the hole with the number 7 tap drill to make sure the hole is round and the correct diameter. Then I carefully thread the hole with a 1/4-20 tap. Go slow and periodically turn the tap backwards to clear the plastic chips. Backing up the tap from time to time and blowing off the chips will help. Another option is a threaded insert, but I haven’t tried that yet.
The lens is mounted in a short cylinder using a split ring to hold it in place. The cylinder is inserted into the top of the pyramid and adjusted to achieve the proper focus. If you are having trouble with the focus, the first step is to determine the direction of the error. If the focus is better when you hold the loupe up away from the screen, then you can try printing a slightly longer tube. If the error is in the other direction, then you will need to change the lens focal length and reprint the pyramid.
If you are going to use the loupe on printed material, then it is good to print it with a translucent filament to allow ambient light in. Otherwise one should use a dark opaque material to reduce stray light.
The maker should only have to modify the lens diameter, lens thickness, lens focal length, loupe_width1, and loupe_depth1. The rest should be automatically calculated. Depending upon the location of the tripod socket on your camera, you may have to change the bracketbasethickness and the attachlength.
The maker needs to open the file in OpenSCAD and then render and save the pieces while incrementing the phase variable. For example, set phase to 1, render and export the stl file. Repeat this for phase = 4, 5, and 6. I designed the program in this way so that the user only had to enter the parameters once. I also find it difficult to print multiple things at the same time without of lot of spider web filament connecting the parts.
Depending upon your printer and filament, you may need to put a little tape around the cylinder holding the lens or adjust the diameter in the program.
Have fun and good luck.