Washer Stops in Petzval

[Two23]

I need to make some stops for my Derogy Petzval. There is no slot, so I'm planning on making some washer stops to go inside the barrel. The barrel is designed to easily twist apart. I have some black soft foam sheets I intend to glue back to back to make a thin but stiff "blank" to cut apertures into. Plan is to make them a tight fit so they will stay in place. I know they go between the front elements and the rear, but exactly where? Does it matter? I won't be using the focus knob and have been leaving the lens cranked to its shortest position. Can I put the stops over the rear set of elements, which are mounted in their own inner sliding tube? Or, should I fit them into the main barrel, in the middle between the front and rear elements?

The diameter of the main tube is 1.67 inches. The "native" aperture is about f3.5. I plan on making f8, f16, and maybe f32 stops. I need to stop this puppy down so I can get 2 sec. exposures in daylight using ISO 25 B&W film. So, don't I divide the 1.67 inch inner diameter by 1.1416 for each stop, so for f16 I need a hole that is 0.4 inches diameter, correct? I've never done this before and need some help.


Kent in SD

[Richard Rankin]

Why not use a yellow and some ND filters and use the thing wide open? I'm not sure why you would bother getting a petzval to stop it down so it performs more like a much cheaper RR lens.

Richard

[Two23]

Why not use a yellow and some ND filters and use the thing wide open? I'm not sure why you would bother getting a petzval to stop it down so it performs more like a much cheaper RR lens.

I don't shoot portraits, and want the DOF. The stops would give me some latitude for exposures too. I am also going to use a few filters to cut the light as well, both colored and ND.


Kent in SD