2inch Eyepice (from old 10x50 Binoculars)

thingiverse

Eyepiece design: These 2-inch eyepieces were crafted from old binocular objective lenses. I utilized 10x50 and 7x50 to create an eyepiece with a 54mm focal length. Lens Diameter: ±50mm (four lenses required). Lens arrangement: Di Plossl / Double Plossl. Eyepiece field stop: 47mm (not the standard 46mm common in 2-inch EP's, experiment as necessary). Two different objective inserts are available for download here. If your lenses don't fit snugly, remember there is no shame in using insulation tape. Printing details: Recommend printing main body in PLA and inserts in ABS (if possible). Construction: Paint the inside of the eyepiece and front insert black to prevent light scattering off the inner surface. You may also want to blacken the edges of the objective lenses before installing. Although my eyes don't notice any difference, I read that blackening lens edges and inner surfaces increases contrast. As for the screw insert, you can either add a M3 nut and melt it into the plastic, or use proper M3 brass inserts, or just thread the plastic hole to M4... do whatever works for you.