A challenging project, and I can't offer any constructive help with the restoration, but it occurs to me that you might gain some purchase on the threaded sleeve by pressing the end grain of a block of wood against the serrated end.

Surprisingly Opera Glasses are supposed to be very good for observing the night sky, they combine good light gathering with modest magnification so bring faint stars and nebulae into view.

I found this link on the Cloudy Nights forum to 'Astronomy with an Opera Glass' by Garrett Putman Serviss (great name, eh?), together with this wonderful extract:

We shall presently see some examples of star-clusters and nebulæ with which the instruments we are using are better capable of dealing than with the one described above. In the mean time, let us follow the bending row of stars from Antares toward the south and east. When you reach the star Mu, you are not unlikely to stop with an exclamation of admiration, for the glass will separate it into two stars that, shining side by side, seem trying to rival each other in brightness. But the next star below, marked Zeta, is even more beautiful. It also separates into two stars, one being reddish and the other bluish in color. The contrast in a clear night is very pleasing. But this is not all. Above the two stars you will notice a curious nebulous speck. Now, if you have a powerful field-glass, here is an opportunity to view one of the prettiest sights in the heavens. The field-glass not only makes the two stars appear brighter, and their colors more pronounced, but it shows a third, fainter star below them, making a small triangle, and brings other still fainter stars into sight, while the nebulous speck above turns into a charmingly beautiful little star-cluster, whose components are so close that their rays are inextricably mingled in a maze of light. This little cut is an attempt to represent the scene, but no engraving can reproduce the life and sparkle of it.

Follow-up to my last post – looking at Daves photos of the eyepiece, it does appear to be made up from several pieces, if only because the lens appears to have slid to one side.

My glasses look identical to the ones in the photo, but the eyepiece rim is definitely solid, and the outer brass tube goes right down inside it to the lens seat, so there is no possibility, even if it was bent, for the lens to move as shown in the photo, so possibly it is an earlier or later model.

That said, it would certainly be possible to make a replacement from the solid, but cutting the threads would be a challenge. The outer brass tube is threaded internally and externally, and it is very fine thread. Possibly you could make up a rim first from the solid, then carefully cut and turn away your broken rim to recover the original brass tube, and solder that into the new rim.

Can I suggest that as a last resort, if repairs to the brass eyepiece fail, you could make a solid version from Acetal (Delrin, etc). This is a good solid plastic like a more rigid nylon and not brittle like Bakelite – and takes turning and thread cutting wonderfully. And it comes in black and is not so cold on the skin.

Cheers, Tim

I would turn a plug out of scrap material that will hold the ring with serrations round whilst you attempt to unscrew it. You could use slip joint pliers then with no risk of collapsing the ring.

Opera glasses are of the Galilean type, just two lenses, an objective and an eyepiece that can be focused but not to individual eyes of the user. The image occurs inside the telescope and the eyepiece lens is a negative lens that sees this image. To make the image clear they place a 'Stop' inside which takes away the blurry edges. Dust is common as the tubes doe not seal the outside air..

Maybe the first type of telescope ever used, think Galileo who monitored the heavens etc.

Clive

I think achromatic objectives would be useful on Galileans too.

You can examine the lenses from the field end with a single light source behind you, and see how many reflections you can see from the air/glass surfaces. A single lens will show 2, and achromatic doublet typically 3 if the fit between the elements is good – the last one from the back of the inner corrector may be larger and dimmer.

If you see 4 reflections you may have a well-assembled triplet, but if one pair of reflected images diverges more the further it is from the centre of the lens, you've either poorly mated elements or – more likely, at least in the case of telescopes – a doublet that's been dismantled and reassembled with at least one lens ar$e-about-face. I've seen many old telescopes with that last fault.

A good bodge is proper engineering.

The aeroplane and telephone are only bodges for not being able to be in multiple places at once.

Hi, Dave,

When I renovated my OGs, i managed to drop the eyepiece lens when I unscrewed the rim, and it was a right b****r to find it again! Your suggestion of Canadian Balsam just about mirrors what I did.

If yours are like mine, the actual 'eyehole' is somewhat smaller than the lens, so in effect it is sitting on quite a wide seat. I simply cleaned up the seat, positioned the rim so it was horizontal, and sat the lens in place. I then used a sharp pointed toothpick to place a couple of tiny blobs of Evostik (impact adhesive) at the edge of the lens, so it was secured inside the eyepiece 'cylinder'. When the glue was dry, I screwed in the retaining cylinder (the bit you have had problems with), and it worked fine.

I used this as opposed to something like shellac because I didn't want the glue to spread around the lens, and fix it permanently, or get onto the lens itself. Very small drops (hence the toothpick) are easy to remove.

Incidentally, the rim of my lenses were not smooth – they have quite a rough finish, with small chips around the edges – they don't matter because they are masked by the eyepiece rim.

The lens doesn't seem to require any 'alignment' as such. There doesn't appear to be any way to adjust it anyway, and there certainly wasn't multiple lenses or packing pieces – these were sold as a relatively cheap pair of opera glasses – simply clean the seat, bung the lens in and screw down the locking tube. It didn't make any visible difference then or now which way around it went – it looked like a symmetrical concave lens.

Edited By An Other on 07/03/2018 15:01:31

I would have thought that the lens was likely originally bedded onto a deformable and hardening ‘putty’, positioned in place by the screwed ferrule and then cleaned up.