**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.

Step 1:

Jump to a few days later. I have the binoculars at the work bench.  Using a piece of sheet steel, I am able to release the screw that holds the eyepieces to the focusing rod. This allowed the eyepieces to be individually removed from the binoculars. A little more work with a lot of paper towels and some solvent (I used acetone) nicely cleaned up the excess grease. I reassembled the eyepieces and took a look.  I still had trouble fusing the images and the eyepieces were still floppy when adjusting the IPD. Its back to the work bench for me and my new 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.
<p>How do you adjust divergent/convergent axis on binoculars?<br>There are small set screws to adjust vertical collimation, but how can I adjust them horizontally if they are cross eyed or wall eyed (so to speak).<br>I have a cheap pair of Barska zoom binoculars (yeah, I know) which are misaligned horizontally. I expected some sort of eccentric or other adjustment at one of the hinge points, but can't find anything.<br><br>I also just bought a pair of 25x70 celestron binoculars listed as &quot;for parts or repair&quot;.<br>I asked the seller to describe the problem, and it was described as double vision (sort of). I'm hoping they only need vertical adjustment, but if not, I will need to know for them too. </p>
I can't speak to any particular brand of bino but, as described, one of the prism adjustments will adjust the view horizontally which will allow you to correct the issue you are experiencing.
I only have two adjustment screws (one on each barrel)... but I found out that the movement is at 45&deg;, so if I move both screws the same way, it adjusts divergence / convergence. Here is a really good &quot;how to&quot; : http://www.oberwerk.com/support/collimate.htm
Actually, what I found out was that each screw adjusts that side at 45&deg;, so if you adjust both sides in the same direction, it will make them converge or diverge.
I only have two adjustment screws (one on each barrel)... but I found out that the movement is at 45&deg;, so if I move both screws the same way, it adjusts divergence / convergence. Here is a really good &quot;how to&quot; : http://www.oberwerk.com/support/collimate.htm
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.
<p>Hi:</p><p>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.</p><p>William Cook. Chief Opticalman, USNR-Ret.</p>
Thanks for sharing this article, its just what I was looking for. My husband insisted I get <a href="http://superboptics.com/binoculars.html" rel="nofollow">best compact binoculars</a> possible for our huge hunting trip coming up. Well, I did but I bought them from a guy who hadn't taken best care of them so no I need to learn how to tune them up and this was just what I needed! My husband thinks there great ones too, just need a little work. Wish us luck!
Very useful, thanks for sharing.
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.
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.

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Bio: Tinker, astronomer, father, busy body.
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