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Heespharm
11-Apr-2011, 23:06
How do I determine the aperture adjustment?? Spot meter on ground glass? Measure the amount of light falling on the ground glass?

John Kasaian
12-Apr-2011, 01:37
See if Calumet can supply you with a scale?

Dan Fromm
12-Apr-2011, 02:51
Open the diaphragm as wide as it will go. Close it slowly. The marked stop at which it just becomes visible through the front element corresponds to f/9.

Heespharm
12-Apr-2011, 06:06
Open the diaphragm as wide as it will go. Close it slowly. The marked stop at which it just becomes visible through the front element corresponds to f/9.

After that how do I determine the other fstops?

Dan Fromm
12-Apr-2011, 07:02
f/11 is 1/2 stop down from f/9. f/16 is 1 stop down from f/11. And so on.

The scale marks are spaced 1 stop apart. Once you've found the mark that corresponds to f/9 you're set. Except that you should know this already.

Jim Galli
12-Apr-2011, 07:23
Your old scale is usable but it's 1/3 stop off at every stop. ie. when it says you're at f11, slide the aperture 1/3 stop back towards f8, and this is your new f11. One possibility is to elongate the holes in the scale so you can re-attach it in the correct place for the numbers to work. Or simply try to remember to always open a 1/3rd of a stop. Recipe for disaster playing these memory games for most of us, but it's only a 1/3 stop.

Heespharm
12-Apr-2011, 08:02
f/11 is 1/2 stop down from f/9. f/16 is 1 stop down from f/11. And so on.

The scale marks are spaced 1 stop apart. Once you've found the mark that corresponds to f/9 you're set. Except that you should know this already.

I didn't know that the spacing between fstops is the same no matter what elements your using...

Dan Fromm
12-Apr-2011, 08:48
Think about the meaning of f/ numbers and you'll see why.

Struan Gray
13-Apr-2011, 02:25
If it's an original, plain Sironar the aperture scale will be even closer to correct than the 1/3 of a stop that Jim calculated. The switch from the asymmetric Sironar to the symmetric G-claron almost cancels out the focal length change, at least in a back of the envelope calculation. I get just under 1/5 of a stop less exposure for the G-claron.

The difference is more easily measured than calculated. If you have a meter with a ground glass probe attachment, you can compare readings for the two lenses with the camera pointed at a stable light source which fills a reasonable area of the ground glass when in focus. Otherwise, you can take a photo of a greyscale with each lens and compare densities.

I always overexpose negative film by a stop or so, so were it me, I would just get on with using the lens with the existing aperture markings. Add a half stop later if the negs look a little anaemic.

dave_whatever
13-Apr-2011, 06:16
f/11 is 1/2 stop down from f/9. f/16 is 1 stop down from f/11. And so on.

The scale marks are spaced 1 stop apart. Once you've found the mark that corresponds to f/9 you're set. Except that you should know this already.

This assumes that the shutter has stops spaced in a linear fashion - I know some older Compurs dont (more spread out at the wide open end) in which case its a bit trickier. But if its a linear scale you're laughing.

I use a 150mm g claron in a shutter from a 150mm symmar-s. As someone else said, find the point that its just stops being wide open and this is your F9 point, everything else should then fall into place assuming a linear aperture shutter. In my case all the stops were about a stop less than on the scale (i.e. f32 on the g claron is about the same diameter as f45 on the symmar, presumably some quirk of lens design).

Tony Lakin
13-Apr-2011, 07:00
Hi
I have made (Photoshop) a scale for using both 210mm and 240mm G Clarons on a Copal 1 shotter (see below), I have had to reduce the image size to enable to publish it here, if anyone on this forum would like an actual size high res. Jpeg please send your email address via PM and I will forward a copy.

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