How do I determine the aperture adjustment?? Spot meter on ground glass? Measure the amount of light falling on the ground glass?
How do I determine the aperture adjustment?? Spot meter on ground glass? Measure the amount of light falling on the ground glass?
See if Calumet can supply you with a scale?
"I would feel more optimistic about a bright future for man if he spent less time proving that he can outwit Nature and more time tasting her sweetness and respecting her seniority"---EB White
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?Originally Posted by Dan Fromm
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.
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.
I didn't know that the spacing between fstops is the same no matter what elements your using...
Think about the meaning of f/ numbers and you'll see why.
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.
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).
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