ASA - DIN - ISO conversion?

Discussion in 'Film and Processing' started by hansley_yunez, Mar 16, 2004.

  1. How do u convert between ASA, DIN, and ISO? I have a classic camera
    ca.1950s with only DIN and ASA, and they dont seem to be equivalent
    to ISO (i believe they have since changed the formulas and they are
    now equivalent).

    DIN goes from 5 to 650, doubling with every increment.
    ASA goes from 12 to 33, adding 3 with every increment.

    Id like to know what these values are in today's ISO terms. Thanks!
  2. I think you have ISO and DIN backwards. Try here -

    Also, ASA and ISO are very close in value.

    Ron Mowrey
  3. From the kodak link it looks like i have the names reversed, but thats what the camera says. Of course it could be a REALLY terribly designed user interface, but its pretty clear that DIN is 5-650 and ASA is 12-33.

    In any case, ill just take the 5-650 value as the ISO. Thanks
  4. I think they must be reversed. According to my old Sekonic meter, DIN 42 equals ASA 12000. DIN 30 = ASA 800. Anyway, a setting that only went up to ASA 33 would have been severely limiting even in the 1950's.
  5. DIN = 10 * (log ASA) + 1
    ASA = antilog ((DIN - 1) / 10)
  6. The equation Bill shows; is in the ancient SPIE literature. You take the base 10 log of the asa; multiply this by ten; and then add 1.<BR><BR>asa 100 = 21 DIN<BR><BR>asa 10 = 11<BR><BR>asa 1000 = 31 DIN<BR><BR><BR>We learned this in 4H Photo club; about 4+ decades ago. It is mentioned in one of the ancient Speed Graphic books we used. Prior to about 1960; some of the B&W asa specs were different. Once the Kodak films gave Westin; GE; and ASA daylight film speeds; and also a sister set of tungsten film speeds.
  7. odd. have a look at this:
  8. another one with the center rotated:
  9. Are you certain that's assembled correctly? Have you used this camera?

    From a quick glance it looks as if going to a slower film would push you to a smaller aperture, instead of a larger one. That would suggest the plate is on backwards, explaining why the film speeds are labelled backwards.
  10. Going to a slower film would indicate a bigger aperture. If u look at the first pic, rotate the inner disc counterclockwise. The DIN value will decrease from 650 to 5, while the aperture value at the 12 o'clock position will widen from f22 to f3.5 (a little beyond actually). So that seems to be correct. The exposure values on the outer disc are also correctly positioned.

    BTW ive never used this camera, it was my grandfathers. In any case the light meter seems to be kaput, i was just curious to know.
  11. James G. Dainis

    James G. Dainis Moderator

    From the gouge mark on what appears to be the center screw, it looks like someone took that apart and didn´t reassemble it correctly.
  12. From previous reading:
    1) ASA and ISO speeds in modern times are identical.
    2) Back in the 1950's, the speeds were adjusted. Previous to that, they had a "safety factor" built in that tended to overexpose everything. This wasn't simultaneous with the change from ASA to ISO, but was a change in the ASA definitions. I can hunt up more info on this in a couple of books I have. Seems like it was about a stop different.
    3) DIN and ISO speeds are figured using different definitions, so there is not an EXACT relationship between the two. The DIN standards and ISO standards specify the testing methods used to establish film speed, which are different.
  13. Hansley, my mistake -- it'd be easier to play with it than visualize how it bahaves. But I think if you took that plate off and flipped it around then the speeds would be labelled correctly and the aperture values would still change correctly with the film speed. So I think it's assebled incorrectly.
  14. EVERY film box I have seen of used in the last 3+ decades has the iso/din numbers related by the equation Bill and I posted. The legal printed asa/iso's are legally to the nearest 1/3 stop; so. All the film boxes made in the last 3+ decades use this formula.
  15. Thanks guys, i opened it up and reassembled it. A bit more complicated than i expected, but it was indeed assembled incorrectly. Now im trying to figure out how to use this lightmeter
  16. antilog? here we use 10^n...

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