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Post by Peltigera on Mar 2, 2011 12:03:57 GMT -5
I have just purchased (today) a Zeiss Ikon Contaflex Beta and have loaded a trial film. I have a problem, however - film speed setting on the exposure meter. The film I have is ISO 100/21DIN but when I set the exposure meter to 21DIN (there is no 100 marking on the ASA scale) the corresponding ASA number is 40!  Do I go by the ASA (as ISO) or the DIN figure? Or are both wrong? I also have a secondary but not particularly important question - the focussing scale is in feet but the bottom of the lens has meter - which I prefer. Is it possible to remount the lens so the meter scale is against the focussing pointer? Any advice much appreciated. John. |
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photax
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Post by photax on Mar 2, 2011 12:41:58 GMT -5
Hi John,
You are right. I`ve never thought about that problem, because at the time I used this model, films here have been marked with the German DIN. I am just sitting in front of my Contaflex and there is actually 40 ASA vis-a-vis the 21 DIN. But there is also no 100 ASA marking, just 40,80,160 and so on. Sorry, I dont know what that means.
MIK
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photax
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Post by photax on Mar 2, 2011 12:47:56 GMT -5
Hi, Its me again  Just read an article about this problem. The ASA standard had been revised in the 1960`s. MIK |
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PeterW
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Post by PeterW on Mar 2, 2011 16:34:10 GMT -5
You are quite correct, MIK. The ASA/ISO scale of speeds was revised in the 1960s to give a meaningful conversion. Accurate conversion is impossible without rounding the figures up or down because the ASA/ISO scale is arithmetic whereas the DIN scale is logarithmic. Also, the laboratory procedure for testing is different for each system. Each maker of exposure meters had its own method of conversion. After a lot of international discussion it was agreed that if the ASA/ISO number doubled, the speed of the emulsion doubled. In the DIN system, the speed of the emulsion doubled if the figure 3 was added to the DIN number. Makers of exposure meters fell into line. So the accepted comparison for exposure meters (on or off the camera) and rounded up or down to whole numbers started ISO 6 8 10 12 16 20 25 32 40 50 64 80 100 ... DIN 9 10 11 12 13 14 15 16 17 18 19 20 21 ... and so on. The revised comparison scales should be accurate to within a quarter of a stop. Before long, Russian Gost figures were revised to make them the same as ASA/ISO Further confusion was added to the revision when Ilford was persuaded to drop the so-called "safety margin" on its film speeds, a margin it adopted years before to allow for the light transmission through multi-element uncoated lenses. So, overnight, FP4, for example, jumped from 125 ASA to 200 ASA. It was advertised as NEW, NEW!!, but I don't think many experienced amateurs, and certainly no professionals, were fooled. At the same time, Ilford revised its recommended development times for ID11. Some similar confusion among the scales on exposure meters comes from lens makers adopting different systems. There’s a piece about this on my website at www.peterwallage.com/Chit%20chat%20page.htm#fstopPeterW |
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Post by Peltigera on Mar 3, 2011 5:25:38 GMT -5
Thank you for your help - but I am still not clear. Do I use the ASA or DIN figures on the Contaflex exposure meter? Or neither?
[later] OK, finally had the sense to work it out for myself. Compared the Contaflex with my Leningrad meter - DIN is the one that is OK.
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photax
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Post by photax on Mar 3, 2011 11:31:25 GMT -5
Hi John,
As you found out, DIN will work. I did the same with a Gossen Sixtus Sixtomat meter.
MIK
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Do I go by the ASA (as ISO) or the DIN figure? Or are both wrong?
Just read an article about this problem. The ASA standard had been revised in the 1960`s.