Repolishing old lenses with fungus, balsam separation

[kfed1984]

Makes it seems like the excess balsam squeeze out is a big issue. Does it stick to everything that hard? Is it possible to cure the cement without heating the lenses, just by waiting for the balsam to evaporate?
If so, then I can wait a week for the balsam to set hard enough and then soften the 3D printed jig in an oven and peel it off in case it sticks. If I print with PLA, it becomes quite soft by about 80C. Also, PVB 3D printing filament can be dissolved or softened in isopropyl.

[PRJ]

V blocks are the way to go.


If there is any balsam around the glass after you bake it, the balsam is easy to remove.

[kfed1984]

V blocks are the way to go.


If there is any balsam around the glass after you bake it, the balsam is easy to remove.

the v blocks are the way to go for concentric lenses for sure, but the harder one is a combination of two lenses with different diameters.

[Mark J]

I'm racking my brains trying to think how this sort of thing was done in the days before air-bearings and optical alignment telescopes. Have you got access to any of the old textbooks on optical production ?
We have some at work, might have a quick look if I get time.

[kfed1984]

I do have some books on telescope making mentioned at the beginning of the thread. If you find some good books, let me know the titles if you don't mind.

[Tin Can]

Since it is etched into the spheres

Grinding will change the lens from optimal

I have one etched lens, I use the good 1/2

buy another lens

life is short

[kfed1984]

Well, we're not really grinding too deep but polishing, and even if we were to grind then the spherical shape would be retained mostly.
No, that's not how I like to do things, lens polishing makes me more connected to my equipment. Also balsam separation repair is a must, as I have some good lenses with separation.
Also I have some other lenses with micro scratches all over, from bad cleaning. Now that I know how to do this, it should not take too long.

This whole exercise is more of as Zen thing, not about being an efficient photographer. Otherwise I would just get a new lens, yes.

[Mark J]

I do have some books on telescope making mentioned at the beginning of the thread. If you find some good books, let me know the titles if you don't mind.

Yes, however the telescope making books won't deal with the kit required to cement two dissimilar-diameter lenses.
I think we still have a copy of 'Optical production technology' by Horne , at work, i think that's the title.

The principal of optical centring of a doublet is that you have one lens set on a circular 'knife edge' on a precision spindle, then you need to send light down at the lens and view its reflection coming back. You adjust the first lens till its top surface is running true ( the reflection is stable, not moving ) then add the cement and the second lens ; then observe the reflection from the top surface of the second lens and adjust till this is also running true.
I just need to see how this might be done with relatively simple equipment.

[kfed1984]

well if we use the jig to get everything aligned shouldn't that work? after grinding the mechanical and optical axes should coincide. If we re-align mechanically to about 0.001", should that be accurate enough for the optical axis?

[Mark J]

I thought you were hoping to re-cement the 300 Symmar-S above, where the lenses are not the same diameter , or easy shapes ?
What kind of jig did you mean, maybe I need to re-read.

For same-size lenses, 0.001" is pretty good, but only if each lens is also optically true to about 1' to 2' to its ground edge - which is not a given.