View Full Version : Projection Petzval - advice needed

Simon Benton
20-May-2010, 16:21
I recently purchased a B&L projection lens at a very low price - on examination it turns out to be a Petzval lens of 11 1/2 inch FL. I decided it was a Petzval by determining that the front element element is a cemented doublet and the rear element is an air spaced doublet - the curvatures of the glass agree exactlly with the Petzval design. It is 5 inches tall and 2.25 in diameter and casts a lovely image on my 5X7 - the glass is in very good condition.
It has an iris which I would guess was used to darken the slide image when it was used as a projection lens. The iris maximum diameter is 1.75 inches which gives an aperture of approx f6.5. If I removed the iris it would give an aperture of around f5. Should I remove the iris (which would be permanent) and use the lens only at f5 or should I keep the iris and use it at f6.5 with the option of stopping down?
If I have made any errors in calculations or assumptions please let me know - any advice gratefully received.

Nathan Smith
20-May-2010, 16:27
Maybe try it out first and see what you think. If you don't get the effect you're after and want to try it full out then you can do that. I'd hate to do anything permanent and regret it.

Mark Sawyer
20-May-2010, 16:42
I'd consider making a second barrel just for wide open use. It could be rather ugly and still be fully functional.

You might also offer it for trade to anyone who has an iris-less version and would like the adjustable aperture.