strange (Petzval?) lens id

[seven]

Hello,

please help with the ID of following lens -

156986 156987 156988 156989

At first it looks like a Petzval, but the front element is not cemented and is much smaller than the rear, which is air separated and a quality build.
So, the question is - what is it ? A cheap (or early, or both) Petzval where the front group just was not glued ? Or some transition from a verres combines to Petzval ? Or something else :)
A manufacturer id would be also nice.

br,
rado

[seven]

measured FL is 220mm, it is F5 and pretty sharp. A sample can be seen here (https://www.flickr.com/photos/25515421@N02/30530481942/)

[seven]

forgot to mention that it is most probably french.
would appreciate any input !

[Steven Tribe]

I didn't reply earlier, as it would only be guesswork. Still is!

Must be a Petzval. The early designs often had much larger rear lens pairs compared with the front achromat. Screw tgether rear pairs is a more complex engineering job than the more usual lens/spacer/lens/retaining ring.

Air spaced achromats were still popular as objective lenses for telescopes in the middle 19th century, although having 3 thin tin spacers. These may have been lost in connection with cleaning out the inner surfaces during the last century. You might try a paper spacer solution to avoid damage at the glass/glass contact.

The heavy reduction section holding the front achromat looks like it is a from a limited brass casting exercise. There are obvious casting imperfections, which would have been solved in a production run.

One way of confirming origin would be to examine the separate lenses and find out their refractive indices! There is a formula which from surface radii and focal lengths, gives refractive index of the glass. The differences between french and english glass are well known.