Kowa 210mm in Polaroid Copal 1?

[MPrice]

I recently purchased a Kowa 210mm process lens and am working at finding a way to put it into a shutter. From info that I have received here the elements should fit a Copal 1 making the lens a F6.8 rather than F9. My question is: I have found a Polaroid Copal 1 shutter, assuming that the elements do in fact fit, how do I go about converting the aperture sizes/scale to work with the longer lens? More simply stated, is the measured opening size for an aperture constant with focal length (i.e. F5.6 is F5.6 no matter what the length of the lens) or are their sizes related/proportional to lens length? If they are proprtional to lens length is there a table (or formula) of aperture sizes somewhere that I can use to create my aperture scale? Thanks for the help...

[Jim Galli]

Aperture scale changes with length of focus. So f8 on your shutter is about 1/8th of 127mm or 16mm opening. Now 16mm is near 1/13.2 of 210mm so that same diameter would be f13 or what we would term f11 1/2. If you have a spot meter like a pentax 1degree you can get pretty accurate by laying the barrel and the shutter next to each other on a light table. Set your barrel to f11 or f16 and simply put the lens or the 1 degree meter right in the throat. Take and copy that reading. Stick it in the Copal and adjust the aperture blades until it reads the same. Mark that on your aperture or piece of masking tape as your transfered f16. On late Copals you'll notice all of the numbers on the scale are equi-distant. So once you've found one you've nailed them all. Space your rear group approximately 1mm away from where it would seat machanically. When the factory did them they had a 1mm spacer.

[MPrice]

Thanks Jim, that's just the info I was after, any suggestions on what to use as a spacer for the rear element?

[tim atherton]

When I got my Kowa 210 and removed the elements from the barrel, it had a small 1mm brass spacer/thin washer in there

tim

[MPrice]

Ahh, that would be nice. I haven't quite figured out how to get around to the back element in the setup I have so once I have that accomplished maybe I'll get lucky and the spacer will be there. Now if I can only find a Copal 3s for the 305mm. Thanks for the info.

[Ted Harris]

Be careful of the Polaroid #1 shutter. Sometimes they are standard and sometimes they are not. Take yoru lens with you to see if it really fits. Many of the Polaroid shutters have non standard threading, especiallyin the rear. Additionally, some Polaroid shutters do not have aperature blades.

MAke sure to check it out carefully.

[tor kviljo]

Polaroid shutters from MP3 and MP4 repro cameras usually comes w/o aperture mechanism, as they were meant to be used with the tominom and Rondestock Ysaron series of barrel lenses. Polaroid shutters lifted from the CU-5 series of close-up cameras have standard aperture mechanism (but with elongated adjustment lever lever) and usually came with tominon 75mm or 127mm (standard mounted in shutter). The shutters are looking quite identical until one start searching for the aperture-lever (a aperture less polaroid shutter being of considerably less use for remounting lenses)......

Before remounting anly lens/throwing the barrel away...., carefully measure spacing by measuring distance between front and rear rim of assembled lens lens with precise vernier caliper or equivalent so You can keep spacing correct when remounting. Also make measurements of actual aperture diameter compared to f-stops on barrel - unit to calibrate new shutter unit.