[LargeFormat] Compur #1 and Copal #1 for G-Claron 305mm f9

[Clive Warren]

At 23:06 21/01/02 -0800, Frank Filippone wrote:
snip
>There is an equation for the size of the aperture, for a given FL... you
>need this to make the calcs accurately...
>
>OTOH, if you can borrow a 210 lens in a copal 1, you can copy the markings
>on a strip of paper, and tape it to the shutter... This is how I got the
>markings on my 355.... I borrowed someone's lens for a few minutes, and made
>a physical copy....
>
>I like the 305... it is a good lens, but I do not use it often for 4x5... it
>is too short and too long for me.. I use a 110, 210, 450 as the progression
>for 4x5.  I got the G Claron for the 8x10, which I no longer have... ( too
>big to enjoy the experience)
>
>Be aware the image circle with these big coverage lenses.... use a lens
>shade to purposefully vignette the lens, and cut down internal reflections
>and stray light......

The equation I use is:

  diameter of iris opening =  Focal Length/f Number

This is how I discovered that the chap who did the CLA on one of my lenses 
was wrong when he said that the marked aperture scale and the actual f stop 
were matched!  With the shutter speeds spot on it was still 1/2 a stop 
out..... following adjustment  to my measurements and the above simple 
maths, all was well.

So, I am a firm believer in actual measurements - although you can be a 
little off with the less than round iris openings produced by modern lenses 
- just have to average the measurements by eye.  Compare modern irises 
(irii?) to say an Artar or an old Componon enlarging lens with 16+ iris 
blades.........

Thanks for the point about the large image circle, particularly when 
stopped down to f22. Do you think the G-Clarons are badly baffled?  I guess 
any extra non-image forming light is undesirable..... you know that you are 
asking me to put a hole in my favourite black hat!  ;-)

Hmmm.....  450mm, bet that doesn't fit in a Copal #1...........

Cheers,
            Clive