Why ASA/ISO 64?

My wife asked me a question I could not answer.

 

Why is Kodachrome 64, "64"? How did Kodak decide to make that rather unusual

number the ASA/ISO when they first released the film (originally as Kodachrome-

X, I believe) back in the early 60s? Why not ASA 50 or 75 or 100, or something

like that? They already had the ASA 25 film, Kodachrome-II. Wouldn't it have

been logical to make the "other" version of the stuff a nice, neat multiple of

that number, either one or two stops faster?

 

Is there some special thing about a square root number like 64 that I don't

know?

Maybe they figured 64 worked nicely with international shutter speeds 30 64 125 250 500

Weird? Not to a lot of people. The round numbers are: 1, 2, 4, 8, 16, 32, 64, 128, 256, ... :)

ISO sensitivity is decided by photographing gray scale targets and then reading the results with a densitometer. The ISO 64 version was consistently the best according to the sensitometric (sp?) standards. But back in the day many many pros routinely rated K64 at ISO 80 for a more saturated look and deeper blacks --and then we'd bracket like crazy.

 

This was done not just for the technically "best" exposure or to cover one's mule in case of a lab mistake (which also is the reason you should never send all of your film in in one batch) but also for aesthetic effect and emotional impact. The technically correct exposure doesn't always make for the best photograph. Many examples of this can be found at http://www.jaymaisel.com

ASA 64 was the best fit for the Instamatic cameras (126 format). When they finaly got around to publishing the standards for color negative speed, Kodacolor X turned out to be 80 speed instead of 64, but that is no problem with color neg film.

Ron,

perhaps but KodaCHROME (transparency) wasn't KodaCOLOR (color negative).

I think it has more to do with it's progressive ASA/ISO over the years. In my copy of 1940's "Kodachrome and How to use it". The speed is listed as ASA 8! My theory is that it doubled a few times over subsequent decades, and became 64. Of course this doesn't account for Kodachrome 25.

Could be due to the "sunny 16" rule - 1/60th sec at f/16 is easy to work from and extrapolate other combos. Of course, Kodachrome is too contrasty to work in bright sunlight and give acceptable results. K64 is stunning under overcast conditions.

I think it's so that the speed is an integer when measured with both the German logarithmic DIN scale as well as ASA. DIN is done in 3rds of stops instead of halves or quarters.

Historically, ASA numbers followed the doubling of numbers progression - usually. 64 was the target design speed of the film and followed the traditions of Kodak's competitors as well as following its own tradition. Pan-F was ASA 32 when Kodachrome 64 came out. Kodachrome, introduced before Kodacolor, was origionally ASA 8 when first mass marketed.

 

The Kodak Apparatus division (camera) may think it directed Kodachrome X to be 64, but the Kodak park people (film) would be interested in keeping the traditional multiples. The question for the 126 film was would 32ish film speed or 64ish film speed be most useful given the compromises of camera design and costs. And the demands of a cheap camera coaxed a little more latitude out of the film design. Kodak had gone through many proposals of single perf, no perf 35mm film, 20mm film, single index hole (round) or square per frame in 35mm, rectangular vs square formats, each with and without a cartridge in the fifties before arriving at the Instamatic 126 format. They had a choice of normal shutter speeds, f stops, samples of small flashbulbs from the flashbulb companies, and finally decided on what film speeds would be automatically supported by the instamatic cameras by 1963.

 

Yes, Tungsten balanced film seemed to have followed another tradition, and yes, slower speed film get into jumping from ASA 16 to 25 at some point. Agfachrome, made the jump from 64 speed to 50 speed in the 1970s and film companies have followed this pattern more often since then, leaving the Kodachrome tradition by itself.

 

 

______

 

Ellis: In the mid-sixty's, lots of Kodachrome-X was used in the 126 size. Not everybody wanted prints, many amatuers were used to slide shows then, like my folks.

 

By the way - I have B&W negs from the 50s, when my Dad worked for Kodak, with single index sprocket hole, rectangular negs - much more practical IMHO than the 126 they came up with. What were they thinking!?