technical drawing of a lens barrel with Waterhouse stop slot...anyone got one?

[Drew Bedo]

Wasn't there a modern production run of a Petzval design a couple of years ago?

Would there be anything relevant to this project from that?

[Jac@stafford.net]

Not really, Drew. The Lomo Petvals (three or four models) uses a complex CNC configuration. All that is needed for the project here is simplicity.

[Bob Salomon]

Wasn't there a modern production run of a Petzval design a couple of years ago?

Would there be anything relevant to this project from that?

Stills, from Lomo, I have one and I believe that they may have introduced a second focal length.

[pjd]

Having asked for help and advice, and having received, it's only fair to give up update on far I've gone - or how bad it looks!



Here's an image of the worst part of the scratches to the front cell - haven't yet tried the Indian ink yet.



The prototype barrel as it is so far (I painted the outside of the barrel black as my wife laughed when she saw it, the pipe was made by Hyundai group). The L brackets work well even though they look clumsy.



The circle cutter I use for Imagon barrel stops and now Waterhouse stops. It's easy to use as a smaller circle can be cut perfectly aligned within a larger one - just lift the cutter after making the larger circle cut and adjust the arm length.



Inside the barrel with front cell removed.

[pjd]

Back of the lens board. The rear cell is firm against the board centred in the middle of the barrel, so that should be fairly well aligned. The front cell is more difficult. Right now that's just shoved into the barrel and held in place by friction. It's difficult to fix that front cell securely in place partly because I need to leave the variable diffusion ring free to rotate (clamping it at the front to prevent the risk of it falling out would otherwise be tempting).

Jac's suggestion about cutting a section of barrel off, splitting it and fitting it internally for Waterhouse guides was a good one. So good that I took it a stage further, and fitted an extra section internally. The barrel is twice as thick in some parts because of that, and the Waterhouse slot didn't need to be cut 50% of the diameter of the outer bit of pipe as a result.

The pros and cons of this as I see it so far:

Pros
It's been very cheap indeed.
It's light (in weight)
It works, so far as I've tested it (it hasn't left the basement yet)
It might be useful to show to a machinist to give them a better idea of what I want made

Cons
A machinist might well take one look and dismiss me as a passing idiot
Still not quite sure how to fix that front cell in place
Cell alignment must be a bit out
My wife was at first suspicious of why I was spending so much time in the basement; having seen the results, she's now just amused.

Not having tried the lens with film (or even outdoors on gg) yet, I'm not sure how much of a problem poor cell alignment will be. I'm not expecting to use it as a sharp lens, so it might not be a big problem. Writing this it occurs to me that it might be worth trying the lens with the front cell deliberately fitted a little off centre just to see how it goes.

With diffusion ring turned out it gets very fuzzy indeed. Focal length is reduced that way.

Another thing I didn't decide is whether to leave the barrel fairly open or to add a permanent stop (baffle?) replicating the wide open aperture of the factory produced lens. Without a stop this barrel is about 100mm in diameter, the original aperture would have been about 87mm wide open.

Thanks for all comments and suggestions so far.

[pjd]

Also, thanks to Mark Sawyer for very patiently and helpfully sharing information by PM - he's helped create a monster of sorts!

[Fr. Mark]

I have a fondness for this sort of monster. Keep going!

[Steven Tribe]

This is the exactly similarly procedure applied to orphaned lens cells from a "front turn" Dallmeyer 3B - just in Brass. Using the same barrel brass as guide for the WHS meant that the maximum speed was noticeably higher when compared with another 3B. This is even more the case with this version of the 3B which had a bulky iris. The WH slot went almost halfway through the barrel.

[pjd]

This is the exactly similarly procedure applied to orphaned lens cells from a "front turn" Dallmeyer 3B - just in Brass. Using the same barrel brass as guide for the WHS meant that the maximum speed was noticeably higher when compared with another 3B. This is even more the case with this version of the 3B which had a bulky iris. The WH slot went almost halfway through the barrel.

The same procedure with rather more handsome results

Maybe I'll just leave the barrel a bit wider open than original and see how it goes.

[Steven Tribe]

Here is photo of the first system used to hold WH stops in the barrel. It is more visable on this lens than usual as it is a convertible Petzval where the barrel can be split in two exactly there where the WH slot is.
THere is a circular piece with 2 extra straight-edged pieces to guide the brass stops down. The extra pieces has tiny rivets to hold them in place. The edges have a narrow rebate (2mm) to catch the brass stops. This is from a late 1850's Hermagis, but was continued for many Petzvals for a long period.