Calculating opening size for back/front shutter

[jannok]

I want to calculate required shutter opening size for back/front mounted shutter. How to do it?

Lets assume EL-Nikkor 300mm, that has covering powering power 52 degrees, exit pupil is 47mm from back flange. So tan(52/2)*47*2 gives me diameter 45.85mm at back flange. Is it enough or should I also consider exit pupil size (53.9) somehow?
EL-Nikkor 300mm specs

I'm considering buying Sinar auto shutter that has 75mm mm opening and wondering what lenses can I use with it. 300mm f5.6 lens will probably work, but what about 12" f3.8 projector lens?

[Drew Bedo]

Not sure what the problem is.

I would think that for a front mounted shutter, the only requirement would be that the opening be large enough to cleat the front of the lens. Direct measurement with a tape or ruler should be accurate enough.

The same should be true for a shutter mounted on the rear of the lens.

Packard shutters on the back of the lensboard used tobe common. Front mounted curtain shutters were an even earlier solution.

I could be wrong in assuming that a more sophisticated approach is required, and look forward to learning more.

Cheers.

[jannok]

I'm trying to find out if Sinar auto shutter is worth the investment (thinking of 300/360 f4.5 Tessars, 480/600mm f9 process lenses). For that I need to know how to calculate what shutter opening needed for back mounting the lens. I think there must be better way than just measuring front/rear glass, as for example 300mm f5.6 EL-Nikkor rear glass is ~85mm (shouldnt work with 75mm back mounted shutter), but DB mounted Sironar 300mm f5.6 lens works with 75mm opening of Sinar auto shutter. And if shutter opening is not big enough, does it vignet or is actual lens aperature reduced? If it's aperature, then how to calculate it?

Fixed link for 300/360mm f5.6 EL-Nikkor specs (https://flic.kr/p/oqbgYG)

[ic-racer]

Calculation will be difficult because of the uncertainty in the rear or front nodal point. If you actually know these measurements then it is simple geometry.
That 300mm El-Nikkor is an enlarging lens. Many times one can find a used 300mm camera lens mounted in shutter for less than the price of a new mechanical shutter. It is a very common focal length.

[mdarnton]

" I think there must be better way than just measuring front/rear glass,"

Honestly, I can't think of a better way to know if something fits than to measure it. . . other than by actually trying. I think what you meant to say is "I think there is a more roundabout, complex, and difficult way that won't give a better answer. . . " There's no magic here, and you are making it way too complex. If the hole is larger than the glass, and the glass is against the hole, then there will be no problem. The farther the glass is from the hole, as with an eye at a keyhole, the more the image circle will be cut off, so don't do that.

My 36cm/4.5 Heliar's glass is 3" across at the back, and it mounted as closely as possible to a 3" Packard--about 3mm ahead of the blades, in my case.. If there is any loss, it is theoretical, not actual. That's how it's done. If you never use a lens wide open, this is even less of a consideration in reality.

[Drew Bedo]

Ocaisionally I use a Wollensak 390mm/f5.6, but it is mounted in an Alphax leaf shutter. Lenses of similar specification were made by Schneider in 240mm and 380mm, and don't seem to be too high .

Do you have the 300mm process lens already and need a shutter solution? Do you want to use the Sinar shutter withother lenses?