Quick room temperature lens separation

[RedGreenBlue]

I have a number of old lenses with severe separation. It's a shame to see them idling away on a shelf. I've considered getting them back into service but hesitated for fear of breaking the glass. Over the years I've read probably every available description on how to separate and recement lens elements, so finally I took the first step - a trial separation.

I wanted to find a way to separate lenses without heating them. I'd read that I can soak them in acetone or other solvents for say, up to a week, and sometimes they will come apart, sometimes not.

I have an ultrasonic cleaner that I use for cleaning camera parts. It's incredibly effective at removing stubborn deposits. So it finally dawned on me that it might make short work of dissolving Canada Balsam. And it did.

I experimented with the front doublet of a very trashy projector Petzval. The elements are 1 1/2" in diameter. I removed the lens from the mount, poured denatured alcohol to cover in a plastic cup, and set it in my ultrasonic cleaner. I ran the cleaner for 12 minutes, more or less. I looked at the lens and noticed that alignment had shifted a bit but I was unable to apply reasonable force to separate the elements.

So I ran the cleaner for 12 more minutes. Inspecting again I could see maybe 1/3 of the balsam had been dissolved away but they still wouldn't separate.

One more time, again 12 minutes (the max time on the cleaner dial). I reached into the cup to pull out the lens and as I did one of the elements flew across the counter; the other element was between my fingers. I couldn't believe it. I was happy to find that the flying element was undamaged.

The elements were amazingly clean and slick. There was no gummy balsam residue to clean off. There were small areas with a whitish film that I removed by rubbing with a towel soaked in alcohol.

I'll experiment now with lenses that I care about. I have a nice Darlot Petzval with central separation that I've wanted to repair. The elements are 2 1/4" in diameter. It has yellow separation around the circumference, which I otherwise wouldn't care much about but the central blobs bother me. I think the edge separation will give the alcohol easy access and the lens should separate quickly. But we'll see.

I considered using acetone but apparently I was out of that so I used the denatured alcohol. Now that I know alcohol works, I won't bother with he more (ob)noxious acetone.

I attached pics of the lens with separation and the separated elements. Also, a shot of the Darlot separation that I hope to repair.

...Scott

[cowanw]

Before you start draw a pencil line across the several elements, so that lining them up is simpler when you put them together..

[Steven Tribe]

Before you start draw a pencil line across the several elements, so that lining them up is simpler when you put them together..

This is absolutely unnecessary! Makers made their lenses in such a way (Rotation) that the relative position of the matching surfaces to each other is of no consequence.

The method sounds interesting, but I have experience occasional quick separations in zylene. Acetone, I find to be a little unpleasant to work with (very quick evaporation). Yellowing around the edges often conceals hard deposits which are not soluble in either zylene or water.

[RedGreenBlue]

Just to be clear, I used denatured alcohol. I thought it would be slow acting so that's when I thought to try the ultrasonic cleaner. I really didn't want to use acetone zylene unless I found it was necessary. I'll be trying some possibly more difficult to separate lenses in the near future and can report back as to whether the cleaner with alcohol method could do the job.

Scott

[cowanw]

This is absolutely unnecessary! Makers made their lenses in such a way (Rotation) that the relative position of the matching surfaces to each other is of no consequence.

Is this true of very old lenses such as a nineteenth century hand ground achromatic doublet?
It may help to keep the lenses in order and direction, if you are less experienced, or of faulty memory. Or not.
Some telescope sites say to do this as well but I suppose it is just an old tale. I defer to you of course.

[Nodda Duma]

As a lens designer, I second the suggestion to mark the sides to ensure proper orientation. Every technician I’ve observed / trained rotates the elements to minimize wedge / optimize alignment of the optical axis. This was done long ago as well.

[Steven Tribe]

As a lens designer, I second the suggestion to mark the sides to ensure proper orientation. Every technician I’ve observed / trained rotates the elements to minimize wedge / optimize alignment of the optical axis. This was done long ago as well.

OK, but I am used to recementing with lenses over 100 years ago, which have obviously been recemented at least once before in their working lives. I doubt that they are in the same allignment as they were originally! I have never come across the orientation activity with cementing prepared lens in literature describing optical workshops. Plenty about physical and optical checks of surfaces and of lens assemblies, though.

I have seen dozens of numbers, names of workers/company and dates written in ink or pencil on the sides of lenses, but never a mark across the two lens making up an achromat showing the "correct" allignment.

[Nodda Duma]

OK, but I am used to recementing with lenses over 100 years ago, which have obviously been recemented at least once before in their working lives. I doubt that they are in the same allignment as they were originally! I have never come across the orientation activity with cementing prepared lens in literature describing optical workshops. Plenty about physical and optical checks of surfaces and of lens assemblies, though.

I have seen dozens of numbers, names of workers/company and dates written in ink or pencil on the sides of lenses, but never a mark across the two lens making up an achromat showing the "correct" allignment.

I wouldn’t expect to see an alignment mark, either. There’s no reason for marking during alignment / assembly in the cases when the optician does align them, sets them and moves on. However, there is reason for inspection marks and tracking serial #’s on the elements prior to bonding. Consider also that zeroing wedge / optical misalignment in a doublet can involve bonding and *then* edge grinding. None of which requires edge marking of any kind depending on the practices of the individual shop.

I’m not speaking from second-hand knowledge, as you can probably guess. As I’m sure you know, in specialized fields there’s a difference between what is practiced and what is in the literature. Either take my recommendation or not, it’s no skin off my back!

Regards,
Jason

[jarl33]

I wouldn’t expect to see an alignment mark, either. There’s no reason for marking during alignment / assembly in the cases when the optician does align them, sets them and moves on. However, there is reason for inspection marks and tracking serial #’s on the elements prior to bonding. Consider also that zeroing wedge / optical misalignment in a doublet can involve bonding and *then* edge grinding. None of which requires edge marking of any kind depending on the practices of the individual shop.

I’m not speaking from second-hand knowledge, as you can probably guess. As I’m sure you know, in specialized fields there’s a difference between what is practiced and what is in the literature. Either take my recommendation or not, it’s no skin off my back!

Regards,
Jason

For what it's worth:
https://youtu.be/VfcroN5iwgM?t=588

[Nodda Duma]

For what it's worth:
https://youtu.be/VfcroN5iwgM?t=588

I’ve seen that one before... it’s a classic. Starts off with the centering...on a very similar machine to what I learned centering on. The amount of touch labor (and without hair covers or finger cots!) they had back then on their production lines makes me cringe. You couldn’t make them like that today for any reasonable type of cost....not even in China! But.. a prototyping shop would look like that.