Wheel diaphragm f stops?

[Syntax]

I have a R.O. Co #2 lens with a wheel diaphragm [4 stops] on a Marvel Camera, any literature or ideas on the f stops for this model lens? Also a B.C. Co. 5 x 8 [3 stops] on a ROC New Model View camera. Neither wheel has any markings.

 

[removed account4]

Hi Syntax
Are there any numbers or markings at all on the wheel ? (sometimes they are hard / impossible to see)
Take a look at this page: https://en.wikipedia.org/wiki/F-number
You might also try to decipher the focal length ( if you don 't know it already ) and measure the hole and do the N=f/D to get a ballpark
and then look towards the bottom of the page and check what you have against the list of all the funky f number systems that were used.
While I'm not familiar with your specific lens but you might see if the "Stoltz" numbers have anything to do with it...
years ago I had a lens I couldn't figure out the numbers for Andrew Glover ( dagor77 ) told me about stoltz and it was it!
good luck with your fun lens!
John

 

[Syntax]

Hi Syntax
Are there any numbers or markings at all on the wheel ? (sometimes they are hard / impossible to see)
Take a look at this page: https://en.wikipedia.org/wiki/F-number
You might also try to decipher the focal length ( if you don 't know it already ) and measure the hole and do the N=f/D to get a ballpark
and then look towards the bottom of the page and check what you have against the list of all the funky f number systems that were used.
While I'm not familiar with your specific lens but you might see if the "Stoltz" numbers have anything to do with it...
years ago I had a lens I couldn't figure out the numbers for Andrew Glover ( dagor77 ) told me about stoltz and it was it!
good luck with your fun lens!
John

Thanks for the link, no marking on either wheel unfortunately. I would have thought with the popularity of the ROC lenses someone has had to have already figured out the stops, and no info in the ROC sales catalog either.

 

[voceumana]

The approach is a variation on the waterhouse stop system. See: https://en.wikipedia.org/wiki/Waterhouse_stop

You can determine the f number using the focal length and diameter of the opening and calculate; if the lens is a 2 inch focal length, and the diameter of the opening is 1 inch, then the f stop is 2; the calculation is (2 inch focal length) divided by (1 inch opening) equals f/2.

You measurement of the holes need not be extremely precise, since they are probably on the regular spacing of f/ stops.

 

[Syntax]

I have a R.O. Co #2 lens with a wheel diaphragm [4 stops] on a Marvel Camera, any literature or ideas on the f stops for this model lens? Also a B.C. Co. 5 x 8 [3 stops] on a ROC New Model View camera. Neither wheel has any markings.

So for future reference the Rochester Optical Co #2 lens [landscape] with rotating diaphragm has f stops of f16, f20, f26.6 & f40, this was based on a 10” focus [254 mm] from the original catalog literature.
The B.C. Co. 5 x 8 lens [same size as ROC #2] based on a 10” [254 mm] focus has f stops of f20, f26.6 & f40, based on my math, thanks for the help everyone.

 

[Syntax]

I think I’m confusing focal length with focus length on the calculations.

 

[Syntax]

I was wrong on the focal length, it is 11” not 10 making the ROC #2 f stops f18, f22, f30 & f44
The BC Co 5 x 8 lens also an 11” focal length has f stops of f22, f30 & f44