Repro Claron Question

[Kevin Crisp]

I have several of the 305mm versions. One of them is quite different from the other two. On the odd one, the rear element is held in by a black collar, holding a a coated round piece of glass, kind of like a UV filter. The piece of glass is just a piece of transparent glass with no correction that I can see. If you unscrew it, the rear element will fall out of the barrel. I am currently UV treating this lens to get the tea stain out. Under a UV light, this flat piece of glass will fluoresce like crazy, a bright glowing disc the color of Mountain Dew.

Anyone know the purpose of this kind of construction? I obtained a factory pamphlet circa 1969 and nothing in there looks like this. I did ask this question a couple years back, I know, but the UV effect is a new factor.

Thanks.

[otto.f]

Perhaps it has to with the radioactivity this Repro Claron lenses are said to contain, at least the 9/210 I have. I wonder though if that can be an issue because there’s a half-life of 9 years I learned from this forum somewhere. And these lenses are from the sixties, no? If I were you I’d throw away that neutral filter.

[Daniel Unkefer]

I just got a nice 305 Repro Claron from the UK, with calibrated professionally Compur shutter beautiful aperture scale also calibrated for my new 165mm barrel Schneider Angulon. Double duty shutter beautiful condition. For my 4x5 Plaubel Profia cameras

I know these were prolly from the Graphic Arts industry prolly Dialyte 45 degree optics perhaps adjusted to work best at average copy-size reproduction ratios. I work forward to investigating the Repro Claron further. Has a very good reputation

Also have the original Repro Claron graphic arts barrel mount engraved correctly and a perfect condition 165 Angulon Schneider barrel

Might work OK on 5x7

[Neal Chaves]

I just obtained a nice 210/9 Repro Claron #9959440 in Synchro Compur. Just mounted it and will be looking at it on the 8X10 camera later today. Glass is crystal clear. I was surprised to read about possible radio activity so I checked it. I've always had a rad meter of some kind around since the 70s. Like everything else, new ones are tiny, inexpensive and loaded with features. MY GQ GMC-500+ averages 19 counts per minute background in my lab, and 26 CPM at the lens. Not too bad.

[Kevin Crisp]

What I am wondering about is why any lens manufacturer would put a clear piece of glass on the back of the lens like this. It clearly is never intended to be removeable, as the rear group falls out if you take it off.

Neal

I think you will find that 210 R Claron isn't going to get close to covering 8X10. It did test it on 5X7 with no movements and it was very sharp edge to edge at infinity. It makes a great 4X5 compact 210.

[Doremus Scudder]

... If I were you I’d throw away that neutral filter.

If the "neutral filter" is original equipment and part of the lens design, and especially if it holds the rear elements in place, I'd recommend you keep it

The rear filter element is certainly coated (or it wouldn't fluoresce) and designed to do something important, from color-correction to removing aberrations like color fringing, etc.

Maybe Dan Fromm or one of the other lens gurus here will chime in with their expertise.

Doremus

[Dan Fromm]

Doremus, thanks for the kind word. So you'll know, when I look at myself in the mirror I don't see a guru, I see a silly old man.

I think you're right about the rear element, especially since it hold the rear group in.

[otto.f]

“ especially if it holds the rear elements in place, I'd recommend you keep it ” yes!

[Mark Sampson]

I always understood that lenses which used thorium glass had those elements internal to the lens- not least to let the external elements absorb the radiation. The thorium glass-containing lenses that I'm most familiar with, for the Kodak Beacon Precision Enlarger, were designed that way.
Perhaps this mystery element serves the same purpose? Which would not explain why this one is different from other Repro-Clarons.

[Greg]

Under a UV light, this flat piece of glass will fluoresce like crazy, a bright glowing disc the color of Mountain Dew.

In the past I have illuminated many of my lenses with short and long wave UV lights and some glass fluorescing was quite common among 1950s and later optics. To this day I have never read a good explanation of what caused the fluorescence. I always assumed that it was the lens coating and not the glass but could be wrong about that.