B&L 15" f/3.8 Projection Petzval - Looking For Info

[jcoldslabs]

I'm looking for information on the lens pictured below--date of manufacture, original purpose, potential as a portrait lens, etc. It is definitely a Petzval and not a triplet as some of these early B&L lenses are. The front glass diameter is 3 15/16" which, when divided into the 15" focal length, gives a maximum (and only) aperture of f/3.8. It weighs around seven pounds. Clearly a projection or magic lantern lens as there is no slot for stops. It seems to cover 8x10 just fine using the point-it-out-the-window-and-see-how-big-an-image-gets-projected-on-the-wall test, although I have not properly mounted it on a camera yet. Without a flange I'll need to mock something up. I'm hoping to use it on a Century 10A for portraits.

I've included close-ups of the focal length marking, the B&L logo and serial number. Instead of being mounted into an outer tube with the rack gears for focusing embedded in the barrel, there is a large metal ring where the flange would attach at the rear and a rack and pinion mechanism that sits proud of the barrel, if that makes any sense. I've done what research I can online and cannot find any other information on this. Jim Galli mentions a 15" B&L f/4 Petzval on his site, but there are no photos of the lens itself or other descriptive details.

Thanks,

Jonathan

http://www.kolstad.us/ebay/B%26L-Petzval-02-SMALL.jpg

http://www.kolstad.us/ebay/BL-15-In-Petzval-04.jpg

http://www.kolstad.us/ebay/BL-15-In-Petzval-05.jpg

[Richard Rankin]

Have you taken it apart and verified that it is a petzval. Looks more like a triplet to me. If so, there will be a middle glass the same on both sides. A petzval, of course, will have two rear elements close together at the back.

Richard

[jcoldslabs]

Richard,

I have only been able to remove the front element so far and it is in fact a cemented pair. There is a slight ding in the lip of the rear barrel that has made it difficult to unscrew the rear element. All I can tell you is that there is a cemented pair at the front with nothing else in the barrel except the rear element. I have to assume this is an air spaced pair at the rear (which would make this a Petzval). Definitely not a triplet. If the rear pair turns out NOT to be air spaced, then I guess I have something else altogether. I will try more forcefully to remove the rear element to help confirm the Petzval construction.

The marked focal length matches the actual focal length, so the rear elements are not installed backwards or missing any components. I get a sharp center with radial falloff which also makes me think this is a Petzval. But I am not an expert, so I'm still wondering if anyone can tell me more about this lens.

Thanks,

Jonathan

[jcoldslabs]

To partially answer my own question: it appears that this lens was part of a Bausch & Lomb "Convertible Balopticon" projector circa 1913. According to the photo below it mounted in a vertical orientation which is probably why it does not have a full sleeve/tube to support it for focusing since it was not intended to be mounted horizontally. I'll have to keep this in mind when mocking up a mount for it.

A rather amazing looking aparatus:

http://www.kolstad.us/ebay/Convertible-Balopticon-1.jpg

Detail showing the lens:

http://www.kolstad.us/ebay/Convertible-Balopticon-2.jpg


(Image courtesy of Wikipedia.)

[MrDen]

And finally, what was the answer?