What is this lens design?

[Joe Smigiel]

I have a brass Bausch & Lomb projection lens made for the Nicholas Powers Company. It sits about 6" high and ~ 3" in diameter. I thought it was a Petzval design but it looks flipped around and the thick rear pair is not cemented although they fit together with no air space. The front pair has a metal spacer ring. It looks something like this:





The diagram in the vade mecum that seems to match best is Q4 which is a Petzval design with different-proportioned elements and a reverse order. Were any Petzvals non-cemented and is that what I have here? The rear pair is marked 28 In E.F. and focuses at ~28" as expected. The front group seemed to form an (dim) image around 40" and when combined, the lens has a back focus of about 16".

[neil poulsen]

It can probably be found in Kingslake's book the History of The Photographic Lens.

[Steven Tribe]

This is a Petzval.

There is some evidence that some projection lenses were sold with reversed achromat and "rear!" pair.

A few early achromats (for telescopes from the late 18th century) were made with minimum air spaces (pieces of tin foil) or with oil between the lenses.

In your case, the balsam layer probably failed (near the lamp/burner heat source?) and the projector owner just cleaned off the internal balsam layers. Or perhaps Powers ordered it this way to avoid complaints from customers.
You should reverse the cells for photographic use - if you can.

[WootSK]

Petty shock to learn if it is a petzval. Thought that dallmeyer are the starter for the inverting of petzval only to find petzval has done so themself before except it is on both side.

[Joe Smigiel]

Makes sense Steven. Thanks.