14" Red Dot Artar Problem

[RicT]

Good Day Forum Users
I have just acquired an old Goerz Red Dot Artar Lens (14"). The rear element of the lens looks as though the coating (or surface) has undergone degradation, causing an uneven film (that looks something like the scum that you sometimes see on stagnant water - (sorry best description I could think of). I have been able to remove the offending element and inspect it closely - it is one of the rear group. I was wondering if it would be possible to use some microfine abrasive paste and gentle polishing to remove the few molecules thickness on the surface that seem to be causing this - or would this completely destroy the lens- I am willing to give something a go because the lens is pretty well unusable at the moment.
Also the front part of the lens is extremely tight and so far I have not been able to remove it. Any suggestions on that one?
Regards,
Ric T

[Archphoto]

Q 1: copperpolish can help at times. Use it evenly and with a cotton sheet.
I have used it a couple of times, the important thing is to "treat" the whole surface, not a part of it.

Q2: go to micro-tools (http://www.micro-tools.com) they have a lot for camera and lens restauration.

Hope this helps you on your way,

Peter

[Steve Hamley]

In my experience, no. Part of the coating is gone or damaged and nothing will replace it. If the element is clean, it's as good as it's going to get, removing more coating won't help. Try to find another coated something you can try it on before the Artar. A scrap of framing glass, old eyeglass lens, etc.

If you want it fixed, John Van Stelton at Focal Point (google focal point lens) can recoat it. Not cheap - probably $180 - but it solves the problem.

Cheers, Steve

[John Schneider]

The coating thickness is 1/2 the wavelength of (green I believe) light, so only about 275nm - it won't take very much polishing before you've totally removed the coating. I also would leave the "degradation" alone.

If the degradation you're talking about is actually oxidation (and only a picture could confirm this), then even more reason for leaving the lens intact. Natural oxidation on old lenses was noted to increase transmittance, and was the inspiration for coating lenses.

As for unscrewing the lens barrel, I use a pair of strap wrenches.