Mystery lens of the morning

[Dan Fromm]

Galli's Disease may be transmissible.

This morning I went to our local flea market, still open in spite of the temperature, and came away with a $1 treasure. Namely, a lens in brass barrel with slot for Waterhouse stops. Focal length around 10-11", f/8 +/-. No discernible engraving.

So I cleaned the thing up and looked at it. I'd say it was a Rapid Rectilinear type because the elements look like menisci, concave to the stop. Thing is, though, they look like menisci. Singlets, not doublets. At any rate, I can't see a weak reflection from the glass-cement-glass interface each would have if it were a doublet. Checked in Cox, who says that an RR is a pair of doublets.

So, what do I have? It passes light and forms an image and nothing seems to be missing except the Waterhouse stops.

Cheers,

Dan

 

[bobfowler]

Galli's Disease may be transmissible.

This morning I went to our local flea market, still open in spite of the temperature, and came away with a $1 treasure. Namely, a lens in brass barrel with slot for Waterhouse stops. Focal length around 10-11", f/8 +/-. No discernible engraving.

So I cleaned the thing up and looked at it. I'd say it was a Rapid Rectilinear type because the elements look like menisci, concave to the stop. Thing is, though, they look like menisci. Singlets, not doublets. At any rate, I can't see a weak reflection from the glass-cement-glass interface each would have if it were a doublet. Checked in Cox, who says that an RR is a pair of doublets.

So, what do I have? It passes light and forms an image and nothing seems to be missing except the Waterhouse stops.

Cheers,

Dan

Yup, it's a serious disease. You are, however, in luck. I am immune to the virus, so feel free to send your $1 optical finds to me and don't worry about getting sick.

Anyway, RR lenses are a pair of doublets. If you have a way of mounting it up, shoot a 'roid and see if it's a keeper. The RR isn't the sharpest knife in the drawer, but they are wonderful for portraits.

 

[Ole]

The cemented interface in RR's is very strongly curved, so it's easy to overlook the tiny reflection from it.

It could also be a Periskop, two positive menisci. Those are usually much shorter (squatter) than RR's, the elements are in other words closer to the stop. But that can be difficult to determine unless you have a RR or Aplanat to compare it with.

The RR isn't the sharpest knife in the drawer

Except in the central 10°, where they are sharper than most Anastigmats...