View Full Version : Petzval lens modification

14-Apr-2013, 08:58
I recently acquired a beautiful 8 1/2" Darlot lens. Everything is perfect about it but I'd love to have a faster aperture. The lens is pretty basic, one group at the front, one at the back, Waterhouse slit. But inside the lens, next to the slit is a strange flat ring that has about 2" opening. It looks like it's there to hold Waterhouse stops but it can potentially be easily removed making the lens from F4 to something around F2.7. So I'm wondering, is there any functionality for that ring at all and is it going to affect lens performance if I take it out? I don't think I'll be able to put it back in so trial and error isn't an option here.

Steven Tribe
14-Apr-2013, 12:35
Photo please!
These surrounds for Waterhouse stops are to prevent light leaks round the edges - as well as reducing the aperture to what the maker considers is appropriate for his design and customers' requirements. These inserted rings can be single or double, can be pressure fitted or soldering in.
You can put it in again, but it takes time.

Tracy Storer
15-Apr-2013, 08:37
Making a substitute "uncorked" barrel, even a temporary one out of cardboard, would be a great idea to see whether this is a worthwhile idea. No harm to the original barrel unless/until that's determined.

15-Apr-2013, 09:50
Thanks for the great idea, Tracy.

Here's the photo


Mark Sawyer
15-Apr-2013, 11:01
Two thoughts:

1.) Look down the barrel from the front and check if the inner baffle really restricts the aperture. I have several similar Petzvals (Darlot, B&L, Cooke) with baffles like that, but the front element magnifies the aperture such that they don't block any image-making light. (That strong front positive is converging the light through a smaller area as it passes through that part of the lens system.)

If you could, photograph the lens directly through the front from at least portrait distance, (four feet or more), and we can see how much it's blocking the light path to the exit pupil.

2.) Looks like that sucker's really soldered in there! If it does block light, I'd consider taking the barrel to a machine shop and having them mill out the opening to a larger size, so that it will still seal the Waterhouse Stop edges, but be more open. It seems a shame to alter a historic lens, but if it makes it more useful to you, it's not a drastic operation.

Just thoughts...

15-Apr-2013, 11:19
Actually, I found that it was just pressed in there but a bit stuck because the grey coating inside has deteriorated. So I removed it just in case and will test the lens in the nearest future. Big thanks for your ideas!