HUGE Voigtlander Petzval - crown missing

[renes]

I was offered to buy a huge Voigtlander & Sohn Wien Braunschweig petzval, no. 21622, which is 15,7 inches hight (40cm) with front lens diameter of 5,1 inch (13cm), it has original waterhouse stop, hood and 9 inch OD mounting flange, but crown lens is missing. Never have seen such huge lens. Both glasses are exellent, brass is blackening but can be cleaned I suppose. Do not know what FL it originaly was, and if such rare Voigltander petzval but with missing crown could be useful and is it worth to pay $900?

[BarryS]

I'm sure it looks impressive, but $900 for non-working lens is too much for photographer. If you were looking for a museum display item, it would be great, but $900 is a lot for a big achromat and a pile of brass. Missing the hood or the flange for a rare lens--no problem, but missing a lens element? Others may feel differently, but no thanks.

[renes]

Thanks.

[Steven Tribe]

If you can find it's twin, get the R1 and R2 and the central thickness measured and the refractive index, then you can procede with getting a replacement made! The glass quality should be no problem as it pre-Schott glass. I don't think these very large Petzvals are that rare - but they don't get out much!

[Emil Schildt]

If you can find it's twin, get the R1 and R2 and the central thickness measured and the refractive index, then you can procede with getting a replacement made! The glass quality should be no problem as it pre-Schott glass. I don't think these very large Petzvals are that rare - but they don't get out much!

:o If I only knew what you were talking about....

BUT I happen to know that the museum of Photography in DK has some really impressive old petzvals lying around....
They were found in a bombed (by mistake) house in Copenhagen in WWII....

Dented an'all - some looks fine though.

I know the manager well - I could ask him to make some mesurements - If I only knew what you were talking sbout...:rolleyes:

[Emil Schildt]

I was offered to buy a huge Voigtlander & Sohn Wien Braunschweig petzval, no. 21622, which is 15,7 inches hight (40cm) with front lens diameter of 5,1 inch (13cm), it has original waterhouse stop, hood and 9 inch OD mounting flange, but crown lens is missing. Never have seen such huge lens. Both glasses are exellent, brass is blackening but can be cleaned I suppose. Do not know what FL it originaly was, and if such rare Voigltander petzval but with missing crown could be useful and is it worth to pay $900?

renes: please let me understand you correctly (being an ignorant, you know):

the crown lens is missing? the crown on the back or the crown part of the front?

If the back, what diameter?

Please excuse my ignorance.. I actually don't know much about this, but I have something I want to check out....

[Steven Tribe]

Both the crown elements in the original Petzval are bi-convex. The first part of the achromat is a bi-convex with quite low radii (R). The last element in the rear is another bi-convex crown with higher radii (flatter). This is typically the lens in the rear which gets damaged because of the thin edge as opposed to the flint element in front of it.

[hansdekort]

http://www.ebay.com/itm/Voigtlander-Petzval-21622-39cm-high-/161030726865

[jumanji]

That's really fun :D. Was it sold AS IS or they made a new crown glass... ?

[Steven Tribe]

This is fascinating.
Possible scenarios are:

-Sold as it was in 2011.
-A new crown glass - I just don't believe this is possible unless they have access to another "Fünfzoller".
-They have made up a missing lens from an old 5" condenser lens. These are quite common, and is the way I would go, if I was into the fraud business.

[Tim Meisburger]

I have a no name brass petzval that was missing the front crown glass. I assume someone pulled it out to use as a magnifying glass. Anyway, I replaced it with a crown glass from an overhead projector triplet, and now I have a petzval that covers about a three inch circle! I should search around and see if I can find someone with a similar lens, then I could figure out the correct R value, because the one I have is obviously wrong.

[Steven Tribe]

A spherometer is something I have been looking for quite some time.
Always seem to be antique (equals cost and doubtful functionality) or to large (made for telescope mirrors)

[jb7]

A spherometer is something I have been looking for quite some time.
Always seem to be antique (equals cost and doubtful functionality) or to large (made for telescope mirrors)

Got to be worth a 15$ gamble...

http://www.surplusshed.com/pages/item/m1535d.html

[Mark Sawyer]

I have a no name brass petzval that was missing the front crown glass. I assume someone pulled it out to use as a magnifying glass. Anyway, I replaced it with a crown glass from an overhead projector triplet, and now I have a petzval that covers about a three inch circle! I should search around and see if I can find someone with a similar lens, then I could figure out the correct R value, because the one I have is obviously wrong.

Tim, the front objective should be about 1.5 to 2 times the focal length of the whole system, and around f/5 by itself. The front achromat of a decent telescope would probably be the best choice short of finding an old element or having one reverse engineered. (Petzval's original design was based on the front achromat of a telescope with a new rear group, and Petzval telescopes are still being made.)

[Steven Tribe]

Got to be worth a 15$ gamble...

Thanks for the tip. I have taken the chance already! Even a faulty instrument can be calibrated for occasional use.
Now I used to be quite good at Geometry in school - time will tell if I still can!

Tim, if it is the front achromat you are missing - send me a PM with inside thread measurements. I have an orphan Petzval cell with a hood about 70mm thread.

[Tim Meisburger]

Great! Thank you Mark and Stephen. I actually have to go to work now, but I'll tear into that thing when I get home and with my new-found, knowledge see what I have. Stephen, correct me if I am wrong, but couldn't I just copy the arc of the glass on paper and then determine the radius from that, either mathematically or empirically?

[Steven Tribe]

Only if you cut the lens in half across the center of the lens, unless you have some kind of mechanical contraption to trace the curve.

I suppose you could measure the circumference with something like a map distance measuring "wheel" and then make a formula with an X and the micrometer measured distance between the two edges. Not very accurate though.