AO Cycloptic Prism/Eyepiece alignment

[geo_man]

Hi all, I picked up a damaged Cycloptic scope when I purchased a nice table boom stand.

The stereo image would not form as the images weren't aligned. One prism was partially loose and was probably hanging out of position.

More out of curiosity than necessity (it also has a damaged eyepiece), I added a dab of silicone aquarium cement thinking that would do the trick. The prism now seems securely attached but it's still out of alignment.

I read somewhere about using a torch to melt the material that holds the eyepiece in place to achieve alignment (I don't think i'll attempt that). Is that the right way or is there something simpler? Thanks in advance for any info.

[PeteM]

Here's how I've repaired these:

1) Pull off the cover (screws may need a bit of penetrating oil, heat, and a close-fitting screwdriver).

2) Inspect the loose prism to see if it is not too severely chipped from being detached. These can still work with a surprising amount of damage around the edges; sometimes with some loss of contrast.

3) Clean everything up.

4) Use the intact prism or one from another scope (open up the other side) to get dimensions for properly remounting. Sometimes you may be able to see residual glue on the prism and use that to replace it and get dimensions. I subsequently use gage blocks, properly dimensioned and along a parallel positioned against the mounting plate, as a makeshift jig to glue things back.

5) Meticulously clean off the prism - 99% alcohol last step -- and the metal plate (sand clean) in prep for re-gluing.

6) I use cyanoacrylate glue ("instant glue") for the repair, but first insert a disc of fairly thick rag paper between the prism and plate (where the old glue glob was). This is to allow some thermal movement. The reason for using this glue is that it can easily be removed with acetone if not properly placed. Could be there are better glues (your silicone?) -- the bond to glass is supposed to be only so-so. However, I've had Cycloptic scopes in (not dropped again) service for a couple years with this method. Further time will tell how well they hold up.

7) Let dry for the full cure period and reassemble. Using the gage blocks or telltale signs from past adhesive should have gotten the images close.

8) Now we're at the point of tweaking the alignment, using heat. The eye tubes were embedded in solder at AO factory. You can see holes to allow a bit of bubbling up at their base. Arrange a target on the stage. I use a pencil type butane torch carefully played at the base to heat the solder and adjust with some sort of small tapping tool. It's fiddly, but eventually you can get things into alignment.

9) If this operation has been done before (Cycloptics were prone to this failure and many have been factory serviced), you might have to add a low temperature solder.

[geo_man]

Thank you, very much PeteM for the thorough and clear response.

My prism was still attached on one side although it could lift on the opposite side. I was almost certain that attaching the loose side would result in perfect positioning. But it didn't. Maybe I'm at step 8.

Thanks again.

[PeteM]

Should have added that you'll want to apply heat with the eyepiece out, then quickly reinsert to see where you are. Don't want to heat up the eyepiece. Probably obvious to you . . . May even want a damp wet rag around to control heat.

[apochronaut]

I replace the screws holding the prism mounting plates with half round ones, and very thin but relatively broad washers. I then make the holes in the plates larger, so I can move the prisms orbitally to align them. It expands the minimum interpupillary distance a bit .

[geo_man]

Thanks guys. apochronaut, does your technique negate the need for PeteM's step 8?

[apochronaut]

That was the whole point of it. I didn't really like the thought fiddling with the eyepiece tube alignment but that method does offer more latitude, if things are really out of whack.

[geo_man]

I thought so, but wanted to be sure! Thanks again.