Need help to ID lens type

[Joe Smigiel]

I have an old brass lens that is about 5" long, rack and pinion focus and marked as 28" E.F. on the rear outside bezel. It would appear to be a projection lens (no iris or slot for stops) with an aperture of about f/12. Engraved:



BAUSCH & LOMB OPTICAL CO.
Rochester N.Y. U.S.A.
MADE FOR
NICHOLAS POWER CO. New York.
40168

At first I thought it was a Petzval, but when I took it apart I found four elements arranged as:
http://my.net-link.net/~jsmigiel/images/technical/power_lens.jpg

The front group is air-spaced and the rear group is uncemented but in contact. Curvatures are exaggerated in the sketch. The curvature is really only obvious on the front element and very difficult to make out on the rear group.

Anyone know what sort of design this is?

[Jason Greenberg Motamedi]

Are you sure it isn't a Petzval that isn't mounted correctly? Someone took it out of the mount and didn't remember how it went in.

[Joe Smigiel]

Are you sure it isn't a Petzval that isn't mounted correctly? Someone took it out of the mount and didn't remember how it went in.

Hi Jason. It has 4 elements in 2 groups, none cemented. Aren't Petzvals 4 in 2 with the front cemented and rear air-spaced (and RRs 4 in 2 with both groups cemented)? Or does the cement not matter if the cells are in contact?

[BarryS]

I think it's a Petzval, too. Some projection lenses have the groups reversed. I don't know about the uncemented group, but maybe it's related to the long focal length--maybe the lens performed well enough uncemented.

[Kirk Fry]

See page 36 of Kingslake. There it shows a similar design (Petzval) except that each of the elements above would be rotated 180 degrees as Jason suggests. Maybe it works ok with them flipped and avoided patent problems.... (I am guessing :-) ) KFry

[Paul Fitzgerald]

"and the rear group is uncemented but in contact."

do they produce concentric interference rings like they were mated? Maybe someone removed the old balsam and re-assembled it backwards.

[Jason Greenberg Motamedi]

Joe, I bought a HBH many years ago which came more or less like yours. The previous owner had cleaned the lenses by soaking them in some solvent. This dissolved the balsam, and then the fool couldn't remember which way they went in. So I bought them reverse, the front in the rear and rear in the front, with the rear uncemented. So, it may have started life as a Petzval...

And, for what it is worth, I remember someone on the CW forum stating that he used an uncemented Petzval for many years, with no ill effects. Not that I would suggest it...

[goamules]

I agree. Also, I've had several of those B&L marked "Nicholas Power" and they were petzvals. You could re-cement them too.

[Jim Galli]

It's just a petzval that someone had put back together bass-ackwards. See them like this all the time. Put the doublet back in front, face the 2 deepest curves toward each other at the rear and put the thin one rearmost. Bingo, a very nice Petzval.


http://tonopahpictures.0catch.com/Smigiel.jpg

[Paul Fitzgerald]

You could also re-cement the doublet and use it in the rear as a 42" meniscus, hope you have the bellows ;-)

[Jim Galli]

re-cementing is a simple job. One time I was in a hurry and cleaned up the glass real well, and poured some wesson oil from the kitchen, just a drop, and let the pieces go together with just the oil filling the gap. It worked fine and I used it that way for a while, then finally got time to re-cement it.