Obscure Question about 305mm Repro-Claron

[Kevin Crisp]

One of my favorite lenses...I now have a sample that is different. At the rear of the lens is an obviously factory ring, which contains what appears to be perfectly flat glass. At first I thought it was untinted, but it does have a very slight tint such as a UV filter from my 35mm days. If you unscrew it, the rear lens of the rear element will fall out, since this rear-most ring both holds this flat filter and keeps the rear group together. I've never seen this in any repro claron. Anybody know why some were made this way?

Serial number is 13,949,xxx. Thanks.

[Kevin Crisp]

I'll also add that this sample, unlike others I've had, is in a barrell with a waterhouse stop slot but also includes a machined fixed aperture disc. Photo shows the glass filter from the back and the rear element that falls right out without the filter in place.