Binocular Tune Up With Collimation

**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.

Comments

[rimar2000]

Very useful, thanks for sharing.

[tholopotami]

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]

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.