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invisibleflash
1-Jul-2013, 04:27
My old light meter broke. I was going to buy a selinium Sekonic. It uses ISO. Does the ISO setting on the new meters = ASA setting for film? Or is the digital ISO different from ASA?

Sevo
1-Jul-2013, 04:39
The full ISO number (e.g. 100/21) combines the ASA and DIN ratings in their 1980's definition. Digital ISO ratings are defined differently, but they substitutable by definition, so that the difference between procedures only would have to interest you if you had to calibrate a camera from scratch without comparison to an already adjusted meter.

ASA and DIN both were significantly reformed around 1960, with old meters and films up to a stop off in some conditions - but in general anything that old will be off by even more due to ageing, and requires recalibration.

E. von Hoegh
1-Jul-2013, 07:04
My old light meter broke. I was going to buy a selinium Sekonic. It uses ISO. Does the ISO setting on the new meters = ASA setting for film? Or is the digital ISO different from ASA?

As far as lightmeters go, ISO and ASA are the same to all intents and purposes. Digital camera ISO may or may not be the same, depending on how the camera's manufacturer calibrates it.

paulr
1-Jul-2013, 08:47
As far as lightmeters go, ISO and ASA are the same to all intents and purposes. Digital camera ISO may or may not be the same, depending on how the camera's manufacturer calibrates it.

Yes! Good point. The tests at DXOmark.com show the differences between nominal and measured ISO. It's usually within 1/3 stop or less, but you'd want to know if you ever use a dslr as a meter when shooting transparencies.

Bob Salomon
1-Jul-2013, 09:07
Yes! Good point. The tests at DXOmark.com show the differences between nominal and measured ISO. It's usually within 1/3 stop or less, but you'd want to know if you ever use a dslr as a meter when shooting transparencies.

Since film speeds are just a suggested starting point the careful worker, analog or digital, should test their system - including the metering system - and tailor it to their preferences. It has always been so. Film speeds were always effected by lighting, exposure, filters, developers, developing time, etc. It was never an absolute.

C. D. Keth
1-Jul-2013, 10:30
Yeah, they mean essentially the same thing right along with EI. They come from different testing criteria but they're equivalent for our purposes and, as Bob writes, they're only a starting point for fine work anyway.

E. von Hoegh
1-Jul-2013, 13:04
Yeah, they mean essentially the same thing right along with EI. They come from different testing criteria but they're equivalent for our purposes and, as Bob writes, they're only a starting point for fine work anyway.

Nay nay. EI is whatever you choose to expose the film at, to suit your requirements, developing, printing, etcetera.
I use Tri-X sheet film (ISO 320) at an EI of 200. ASA, ISO, DIN, GOST, and others are all traceable to certain standards.

Ian Gordon Bilson
1-Jul-2013, 23:01
I have always understood ASA to be what is printed on the package,and ISO to be the rating which gives you the most pleasing results. I know they are not the same,and ISO was invented by some faceless committee in The Hague (?).
I have rarely found them to be the same. The advice to "expose for the shadows - develop for the highlights has always been valuable.

paulr
1-Jul-2013, 23:03
Since film speeds are just a suggested starting point the careful worker, analog or digital, should test their system - including the metering system - and tailor it to their preferences. It has always been so. Film speeds were always effected by lighting, exposure, filters, developers, developing time, etc. It was never an absolute.

True enough for film, but meters are expected to be calibrated to a fixed standard. If you decide you want to expose your ISO 100 film at ISO 64, you still need to set your meter to 64. With a dslr, this will often mean choosing a nominally lower setting.

C. D. Keth
1-Jul-2013, 23:29
Nay nay. EI is whatever you choose to expose the film at, to suit your requirements, developing, printing, etcetera.
I use Tri-X sheet film (ISO 320) at an EI of 200. ASA, ISO, DIN, GOST, and others are all traceable to certain standards.

Yea, yea. If your definition is the truth, then why does Kodak recommend exposure indices for its motion picture film?

Sevo
1-Jul-2013, 23:41
Yea, yea. If your definition is the truth, then why does Kodak recommend exposure indices for its motion picture film?

Easy. To quote Kodak's motion picture film FAQ: "Why is the speed rating of motion picture camera films given in Exposure Indices rather than ASA or DIN values?
There is no ANSI standard to determine the speed of these films.
The speed of motion picture camera films and the suggested filtrations are determined on the basis of practical picture tests."

Jac@stafford.net
2-Jul-2013, 00:16
Yea, yea. If your definition is the truth, then why does Kodak recommend exposure indices for its motion picture film?

Kodak is very careful regarding the statement of film response where exacting conditions are most important. IOW, testing under various circumstances is necessary. We all know that in practice.