So I'm at the Heart of America Star Party. I'm at the swap meet. I'm browsing along and here's this fella with quite a few pair of binoculars and other assorted optical instruments laid out on the table. I look at some lens assemblies and porro prisms, glance at the spotting scopes and find myself at the binoculars. I pick up a pair of 20x60s and look through them. I ask the gentleman how much, fully expecting not to be able to afford them. After about the third time, my mind finally gets the message that yes, they are free. I ask to take them outside for a better look.
Satisfied that the binoculars were usable, I informed the gentleman that I would be glad to take them off his hands for him. A short time after getting back to my campsite, the luster of getting such a good deal was quickly wearing off. I attached the binos on my mount and looked at a distant tree. I almost immediately noticed I was having trouble fusing the two images reaching my eyes. After attempting to adjust the inter-pupillary distance (IPD), and the focus for each eye individually with no improvement in the image, I realized that there was a deeper problem. Casually inspecting the binoculars showed that there was very thick and sticky grease around the right eyepiece housing and adjusting the IPD caused the eyepieces to twist vertically. Still, I was confident that cleaning the dirty spots and lubricating the sticky spots would yield a functional set of binoculars.
A closer inspection of the binoculars revealed that the eyepiece flop was due to a looseness in the focusing mechanism. After removing the eyepieces, the focusing knob can be unscrewed and the entire focusing mechanism pulled out of the binocular body. After much thought on how to improve the fit of the mechanism, I decided to clean the rod and add foil tape to improve the fit into the body. Reassembly after some light lubrication revealed only a small improvement. The majority of the wiggle now seemed to be in the threads of the focuser. Reviewing my work so for, I have cleaned, tightened and lubricated most of the moving parts of the focuser. I am still having trouble fusing the images from each eye.
My eyes are good. Must be collimation.
Before I began, I referred to the book, "Basic Optics and Optical Instruments" which is the civilian reprint of, "Opticalman 3&2" originally printed by the U.S. Navy. It is a wonderful resource for binoculars and basic optical concepts. In it, it describes the navy's method for optical procedures. It describes the use of the Mk I 3x auxiliary telescope to assist in collimation of binoculars. Not having this specific scope is not a problem as any good, small finder scope will work. I used a 6x30 finder with a cross-hair reticle with excellent results.
The goal of collimation is to have both sides of the binoculars pointing in exactly parallel directions. The book I used declares that alignment vertically should be better that 2 minutes of arc (one side pointing higher than the other). The alignment left to right should be better than 2 minutes of arc inward (think of being cross-eyed) and 4 minutes of arc outward (the condition opposite of being cross-eyed).
My free binoculars are now working like a champ. I hope this instructables helps those of you with troublesome binoculars to get them up and running. Good luck and clear skies!