Quote Originally Posted by Ole View Post
Jon, if the focal length of the lens is 24" and the width only 3in, it can be no faster than 24/3 - or f:8. Petzvals are typically about as long as the focal length.

The serial number list in Thiele starts with 27450 as 1884, so it has to be a little before that. Does it say "in Wien" or "Wien & Braunschweig"? Anyway it has to be something made before 1884, which means Petzval Portrait, Petzval Orthoskop, Landscape lens, or Aplanat (Euryskop).

At that time there was only one Euryskop, the f:7.2 - which only went to 1070mm focal length. So that's out.

Landscape lenses are an achromatic meniscus behind the aperture, and came in f:33 only (the f:15 started in 1888), so that's out too.

Petzval Portrait lenses are, as I said, about as long as the focal length and were no slower than f:6.8. So that's eliminated, too!

That leaves the Orthoskop, and Thiele lists a 3" lens of 615mm focal length, at f:11.7. That fits!
Thanks Ole. My lens states " in wein" and I appreciate being corrected for it is an f8 lens when came with an waterhouse slot aperture which at some time I calucated to be f12 given the fact it appears to reduce the aperature from about 3 inches to 2 inches.

Thank you again. Jon