ISO-A vs. ISO

Discussion in 'Film and Processing' started by karl_borowski, Mar 6, 2007.

  1. I'm tempted to buy some of the Kodak Aerial Panatomic-X film at some future
    date. I know it's estar base, probably only available in 70mm, and has
    extended red sensitivity, but I like Estar, don't mind extended red
    sensitivity, or wouldn't mind a filter for the application in which I'd be
    using it, and wish, frankly that acetate films were a thing of the past anyway.

    What confuses me is that it has an ISO-A of 40. I know that thse films are
    essentially developed in D-19 which has the effect of "pushing" them to give
    high contrast images suitable for topography maps or what have you.

    Does anyone know an exact or rough conversion between ISO-A with a developer
    like D-19 and pictorial ASA with say D-76 or HC-110? I know ISO'd be slower
    but by how much?


    Regards,
    ~KB
     
  2. ISO and ASA are virtually identical for most films Karl, so you can use 40 without too much problem. ASA was a measure of threshold speed, and ISO is a measure of camera speed (I hope I didn't get these two mixed up - senior moment here...). If films differ in toe contrast or mid scale contrast then these figures differ substantially, but Kodak has made films with a contrast of about 0.6 for years, and with a pretty constant toe shape.

    There is a bit of math involved in the actual methods of calculation and there is a definition of light source and exposure intensity for each of these as well.

    Ron Mowrey
     
  3. Hey Ron,
    You misread me. I am referring to Aerial-ISO, aka ISO-A, not American Standards Association film speed. I tend to refer to film speed as ASA still anyway.

    ~KB
     
  4. You're right on that the ISO-A speed is for higher gamma. You'll probably have to determine your own EI.
    Did you notice in Kodak's catalog that the minimum order of KODAK PANATOMIC-X AERECON II Film 3412 in 70mm is 18 rolls of 650 feet each? (That might be a whole master roll.) That's going to cost you tens of thousands of dollars, since I doubt anybody has it in stock to sell you one roll...
     
  5. I have a 100 ft 35mm roll of aerecon plus X. I haven't used it. Any interest in that film?
     
  6. Karl;

    I've used plenty of Aerial film, as you know. Probably thousands of square feet AAMOF. We set our cameras at ASA 40 for a 40 speed film, and I found that the same name consumer film for my 35mm camera came out very very close to the actual speed of the aerial film.

    The higher gamma was due to the low contrast of the images on the ground caused by surface haze, so the 'effective' gamma was closer to normal and that is why you can easily use ISO and ASA in this case as being nearly identical for starting purposes.

    You will, of course have to contend with the higher gamma because there is no surface haze to 'cut'. But we also used to develop that film in D-19 or an even higher contrast developer too.

    I suggest you start with 40 and normal development. You will probably get a good image with high contrast. Then expose at about 25 and underdevelop and you will come in pretty close.

    Ron Mowrey
     

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