Is this a petzval?

[Tim Meisburger]

I picked up this lens at a flea market for $20. There was no spacer between the two rear elements, so one was rattling around, and they may have thought it broken. I made a new spacer out of cardboard, and everything is tight now, but I have several questions:

- Is it a petzval?

- Are the rear elements oriented correctly?

- Is this a lens for a slide projector? I assume that is what the slot in the front is for?

- Any idea of a maker? There is no script on the barrel or edges of the elements. Only mark is 6 1/2" on the front cover.

Can it be used in either direction? Seems like the cover could easily be converted to a flange.

[Louis Pacilla]

I picked up this lens at a flea market for $20. There was no spacer between the two rear elements, so one was rattling around, and they may have thought it broken. I made a new spacer out of cardboard, and everything is tight now, but I have several questions:

- Is it a petzval?

- Are the rear elements oriented correctly?

- Is this a lens for a slide projector? I assume that is what the slot in the front is for?

- Any idea of a maker? There is no script on the barrel or edges of the elements. Only mark is 6 1/2" on the front cover.

Can it be used in either direction? Seems like the cover could easily be converted to a flange.

#1 Yes

#2 Kind of. You should flip the outer rear cell so the flatter of the two surfaces is facing the film plain.

#3 Yes

#4 No. It is a Magic Lantern lens Though.

#5 No. You should have the glued pair in the forward position. with air spaced paired in the rear.

[Tim Meisburger]

Thanks Louis! That's very helpful. wonder, do you think I could cut a waterhouse slot in this? If yes, any idea where I would put it? Is there a formula, or is it just midway between the cells?

[Two23]

It would be easier to make washer stops.


Kent in SD

[Steven Tribe]

"It would be easier to make washer stops."
....And these could fit in the wide front slot which was used for thick coloured glass when this was used on a magic lantern. The front assembly can be easily taken apart.
You will have to add a spacer or they will rattle around.
All Petzvals fitted with illumination control used front disc stops before 1860.

[Tim Meisburger]

So the location of the stop makes no difference? That seems strange. Sure it would be easy to make some stops that would drop in the slide holder in the front of the lens, but would that reduce the image circle. Are waterhouse stops, or other stops located between cells, better than washer stops located in fron of the lens?

[Math]

The diagram you drew shows a lens that is NOT a petzval lens. A Petzval lens is a four-element lens, two air-spaced in the back and (usually) two glued in the front. Can you see if the single element (left side on your diagram) is actually two lenses glued together? Often the line where they are glued are pretty clearly visible.

[Tim Meisburger]

Yes, I've since looked at some diagrams on the web, and looked again at the lens, and I'm pretty sure the front element is a cemented pair. I just hadn't noticed it before because it is housed in a brass rim, and because I was not looking for it. I'm not sure, but I might be able to pop it out of there. I'll give it a try later.

[Steven Tribe]

Front stops on a Petzval will gradually reduce the size of the illuminated circle. But I doubt that the "quality" circle will decrease - it might even increase.
I have not experimented with front washer stops on Petzvals - but I know that after 1860 the system was given up within a few years by just about every European maker - which must indicate that the central stop was considered an improvement.

[Tim Meisburger]

Thanks Steven. Once I make a flange and get the lens running wide open, I'll inquire again about cutting slots and making stops, so I can get the petzval operating as originally intended, razor sharp, without all that distracting swirling bokeh...