|4126 forum posts|
Not quite a 'scientific instrument', however I've been asked to look at this pair of Opera Glasses, an optical instrument made of brass and steel with leather grips. As they have sentimental value I don't want to make them worse through ignorance.
The most obvious problem is that one of the eye-piece lenses has slipped out of position probably after being dropped.
The eye-piece itself unscrews easily:
I think the lens is held in position with a threaded inner sleeve. In the photo above the sleeve may be the tube with a serrated top-edge. I've tried unscrewing it but nothing moves.
Can someone confirm that it is a threaded sleeve (rather than glued, soldered or some other construction) and suggest how to loosen it please?
The second problem is that the body of eye-piece is cracking around it's circumference. (More seriously than is visible in the photo.) Due to it's shape I think the eye-piece may have been made by joining a number of brass pressings together and the join is failing. Can anyone explain how it's made or suggest how the damage might be repaired?
|Roger Hart||04/03/2018 15:58:19|
|100 forum posts|
I would say you have got a job on with this one. I agree the lens should be accessible via the serrated sleeve. The snag is that the brass is v thin and the threads fine so any jolt will tend to cross a thread or put the sleeve out of round. I would cautiously grip the edge of the sleeve with a stumpy nose plier and use that to try and undo in the usual direction. Don't overdo it or the sleeve will tear or cockle up. That should free it up till it is finger free. Maybe a taste of light oil before you start.
The eye-piece pressing looks more problematic. My guess is that it is a couple of pressings soft soldered together. The snag is that if you take it apart and re shape it then it will be hard to put it back together any sense. To say nothing of re colouring it. Short of facing that problem I would look to making some sort of shaped stake to go inside and try and 'encourage' it back into some sort of correct shape without doing further damage. As I said, this looks a right job, good luck.
|108 forum posts|
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.
|Richard S2||04/03/2018 16:54:39|
156 forum posts
Farmboy is onto the most likely reason for the serrations.
I suspect the inner lense securing tube was screwed in lightly using a piece of thick leather mounted on a board. the inner tube was then screwed in slowly while the Assembler viewed the position of the lense through the eyepiece.
Often the lense was cushioned in it's seat with a form of putty.
Certainly a challenge to avoid more damage and understanding if it's possible to disassemble.
Edit- you could enquire with these people first - LINK-
Edited By Richard S2 on 04/03/2018 17:01:12
|Neil Wyatt||04/03/2018 17:14:00|
15824 forum posts
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.
|An Other||04/03/2018 18:29:27|
|109 forum posts|
Hi, Dave (SoD) - I have an identical pair of these opera glasses, and can confirm that the eyepiece is held in place by a thin metal tube screwed in. The serrated edge you can see is the top of it. The tube is very thin. I was fortunate, and was able to unscrew mine with my fingers. I think Farmboys/Richard2 ideas are excellent - to use either a piece of wood or leather pressed against the serrations to try and move it. I think using pliers of any kind would be a bad mistake - the tube is very thin and fragile. As a guide to how much you have to 'extract', the inner tube is 13mm long, and the upper 8 mms are threaded. Take care putting it back, its very easy to cross-thread it.
When I first renovated mine, all the tubes which slide or rotate inside others were full of dust, and therefore difficult to turn - only after I finished did I realise that perhaps if I had used some oil to make things easier, this would have ended up as a sticky paste with the dust, and made matter worse - just a thought!
I just took a closer look at the eyepiece of my glasses. I think the eyepiece rim is turned from solid - its certainly heavy enough. The brass tube which protrudes from it (visible in your last photo) fits inside it down to the seat for the lens, and is threaded internally its whole length - it appears to be soldered or press-fitted inside the eyepiece rim. The lens fits inside this brass tube, and is not bedded into anything - it simply sits on the rim inside the eyepiece, and the inner tube (with the serrated top) is screwed down to hold it in place. There is (was) nothing to 'soften' this clamping, such as putty or a leather weather etc, so I guess you must be careful not to screw the inner tube down too tight and crack the lens - as I said, mine were only finger tight - bit stiff to get moving, but then came out easily.
Edited By An Other on 04/03/2018 18:38:42
|An Other||04/03/2018 18:47:30|
|109 forum posts|
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.
|Michael Gilligan||04/03/2018 18:54:17|
12926 forum posts
Although wood and leather are 'traditional' ... May I recommend 'Theraband' rubber sheet as an excellent friction grip.
Available quite cheaply on ebay, if you don't have access to a friendly physiotherapist.
|Tim Stevens||04/03/2018 19:01:23|
1010 forum posts
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.
|4126 forum posts|
Brilliant answers! Confirmed my suspicions about how the glasses are assembled and the need for extreme care taking them apart. Now I know it's a threaded sleeve I'll try turning it with more confidence.
Never thought of using them for star-gazing. Optically they're not impressive compared with binoculars and I'd written them off as a fashion accessory. Hadn't occurred to be that they might be more about light gathering than magnification. Could be - I suppose theatres weren't particularly well lit before electric lighting.
Watch this space. I'm off to apply a dab of penetrating oil ready for an attempt on the thread tomorrow.
Thanks also for advice on repairing the crack and dings. Risky even before considering my low skill-level. I might pass on fixing them.
Looking closely at the glasses I'm impressed with Victorian technology. Neat design, fine threads in thin brass tubes, decent lenses, complicated brass shapes, leatherwork etc. Not hand-made - early mass production of a precision item.
|Ian Parkin||05/03/2018 10:44:07|
606 forum posts
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.
|Neil Wyatt||05/03/2018 10:44:10|
15824 forum posts
It's interesting, I've had a dig and the objective diameter of a galilean system defines field of view, not 'light grasp' - the light increase depends on magnification.
Modern ones (eBay are awash with them) are typically 25mm objectives, while old ones are often 35 or perhaps even 40mm.
It's interesting that the book (based on magazine articles from the late 1980s!) advises getting a pair with achromatic lenses, he also says don't be mislead by a pretty exterior. He recommends trying several well-worn ones as they may be better especially if they clearly got a lot of use.
You can get fully coated 2.1x42 binoculars for astronomy. Not cheap!
Might be worth getting some cheap coated ebay ones though...
|Clive Hartland||05/03/2018 11:10:24|
2427 forum posts
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.
|Ken Biddle||05/03/2018 12:22:06|
|10 forum posts||I repair microscopes with some similar construction. I would use alcohol applied with a swab around the threaded area.Then use a strip of rubber with fingers to turn the tube. If no moveement apply more alcohol and retry. Sometimes these threaded portions are lightly greased and the grease has dried out.Take great care with oil as it may rundown onto something you don't want it on like lenses with difficulty cleaning it off.|
|Mick B1||05/03/2018 13:13:02|
|1001 forum posts|
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.
|4126 forum posts|
A quick report because other diversions and duties have intruded.
The method was close to that suggested by Ken except I used a tiny drop of penetrating oil rather than alcohol. I guessed that the chunky brass construction and simple uncoated glass lens wouldn't suffer.
Once I got it to move slightly a few gentle tighten/un-tighten cycles loosened it and it unscrewed without fuss.
At that point I expected the lens to drop out. Not so, it's been wedged sideways into the structure of the eyepiece probably due to being dropped. I was able to manoeuver the lens almost back into position, but not enough for it to come out. Sod's Law applies - although very hard to centralise the lens, the blasted thing slips out of position at the slightest excuse.
The edge of the lens is damaged around part of it's circumference. As there's no sign of broken glass inside the eyepiece I think it was nibbled to size by a fitter, possibly during an earlier repair.
I'm tempted to glue the lens back into position. I have the modern equivalent of Canada Balsam to hand and could apply it sparingly around the edges with a needle. Be a few days before I can get back to the repair and I might change my mind : it feels like a bodge.
|Mick B1||07/03/2018 10:18:16|
|1001 forum posts|
A good bodge is proper engineering.
The aeroplane and telephone are only bodges for not being able to be in multiple places at once.
|Clive Hartland||07/03/2018 11:15:53|
2427 forum posts
Regarding the fixing of the lens, perhaps use Shellak, This is also used to stop rings and tubes from coming loose. Just a dab about 2 pinhead sizes will do. Easy to soften with Meth Spirit.
No point in coating a Gallilean lens as it is a straightpass lens not affected by colour or distortions as I mentioned they put a Stop in the system to cut off the edges. Also sharpens the view.
If you want a pair of quality glasses the pay a price in the region of £700 to £1000. Sealed, Nitrogen filled and a very good service back up.
In old optical system you may find air spaced lenses. Be careful to keep the spacing pads for replacement, these lenses are affected by chromatics and use the space in between the lens to revert the light back to white corrected light. Here also you will find different types of eyepieces, Ramsden or Huygens with doublet lens.
|An Other||07/03/2018 15:00:19|
|109 forum posts|
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
|Ken Biddle||07/03/2018 23:38:47|
|10 forum posts|
If the lens is held in place by the tube screwing in you may try a method I have used for field repairs. Put a piece of tape over the eyepiece cap outside and press against the lens through the hole. Screw the tube in place and remove the tape. The tape could leave some residue to be cleaned off.
Please login to post a reply.
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.