Instructables
**This is my third instructabe. It was originally written for a magazine but was never published. Rather than rewriting the whole thing, I am posting it  as it was supposed to appear in the periodical**

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.
 
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georgeATM (author) 7 days ago
Pictured here is the auxiliary telescope with the rhomboid prism. This is a very specialized piece of equipment that helps perform the collimation exactly as Mr. Cook describes and is unfortunately beyond the typical home optician. The method I describe will be useful for aligning the optical axes of the two halves of the binos (the most obvious source of eye strain). Carefully aligning the finder body with the bino eyepieces and being mindful of vignetting will help minimize some misalignment during collimation. Adding a right angle prism or two to the finder will NOT improve your collimation.
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Hi:

I want to be nice, but I MUST point out a negative. The 6x30 scope might work out fine . . . IF you had the rhomboid prism attachment, as thoroughly illustrated in your reference. Without that, you can't check the mechanical axis vs. the optical axis. That is the WHOLE point of the procedure. 99.9% of the illustrations on the Internet are well-meaning enough . . . but wrong.

William Cook. Chief Opticalman, USNR-Ret.

rimar20002 years ago
Very useful, thanks for sharing.
tholopotami2 years ago
Useful information! I also needed to calibrate a pair of 7x50 binoculars with good quality lenses but a mediocre focusing wheel (plastic). The problem there , was that the focusing did not move parallel to the lens plane. In some binoculars you need to open in order to reach the prisms. Moving them is a bit scary. The use of the finderscope is a good idea.
georgeATM (author)  tholopotami2 years ago
Glad to give some ideas. You may also be able to tilt the objective lenses to align them with the focusing mechanism. I would caution against this however because it would mean that the eyepieces would also need tilted and I am not sure this is possible.