View Full Version : Projection Lens

Neil Purling
3-Feb-2009, 15:04
This creature may be a Petzval. I removed the elements from the barrel and stuck them in my Polaroid Copal #1. The spacing between the two optical cells in the barrel is not so great so I figured it might form a image I could focus set into the Copal.
The rear cell screwed in the rear of the shutter OK, but the front cell.......
As you can see I used a rubber band.

The lens is approximately 80mm, no idea of speed, perhaps f2.8.
If the beast is actually a Petzval, what sorts of scene will show the swirly effect best?
I have taken some shots, which will have to be processed before I know what I have got here.

3-Feb-2009, 15:14
It looks like it may be the front cell of a triplet projection lens from your photo, but it's hard to tell without seeing more images. Shoot a photo of the sky filtered by dense trees or foliage and you'll see the swirl if it's there.

Neil Purling
3-Feb-2009, 15:45
The barrel was chromed, which makes me wonder if it may be too modern to be the Petzval type.
The scene has to be back-lit to get the swirl effect? Or is the contrast difference something to do with it. If I am doing a shot of back-lit trees I would probably be running at the max 125th exposure of the Copal Press #1 to eliminate branch movement due to wind.

3-Feb-2009, 16:40
A lot of projection Petzvals have chromed barrels and black painted cells. If you have one cell with two air-spaced elements and one cell with two elements cemented together--it's a Petzval. If that front cell has two widely spaced elements and the rear cell only has a single element--it's a triplet.

A scene with a lot of small bright highlights makes it easy to see the lens aberrations at the edge of the frame.

Neil Purling
14-Feb-2009, 14:56
This is a quick n dirty scan off a T400 CN negative, not the most contrasty of materials or it could be the lens.
Do look at that back-lit tree. Definitely worthy of further investigation.
Preferably with a ND filter as well, because the Polaroid Copal has no iris.