Film ISO rating temperature

[edebill]

Can anyone explain what the temperature measurement frequently paired with an ISO rating means? For instance, I have a box of HP-5+ here that says it's "ISO 400/27 degrees". Some Fuji Pro 160S says ISO 160/23 degrees.

Should I be altering my film speed for ambient temperature?

Temperature is on my mind since getting a Jobo - I have to use ice baths to get the water bath (filled with cold tap water) down to 75F for b+w developing.

 

[Nick Zentena]

No. It's the older DIN system. Just ignore it. Unless you've got a meter that lets you set to European DIN instead of ASA. I think ISO is supposed to be a bit of a cross between ASA and DIN so they show both numbers.

 

[Markus B]

It is the sensitivity of the film in the older DIN*-scale values.

33 DIN = 1600 ASA = 1600/33 ISO
30 DIN = 800 ASA = 800/30 ISO
27 DIN = 400 ASA = 400/27 ISO
24 DIN = 200 ASA = 200/24 ISO
21 DIN = 100 ASA 100/21 ISO
18 DIN = 50 ASA 50/18 ISO
15 DIN = 25 ASA 25/15 ISO

*Deutsche industrie norm = German industry standard

 

[edebill]

Thank you! I hadn't noticed that they were all the same for a given ISO.

 

[Roger Hicks]

It's not older: it's still current, though less popular. 3 degrees = doubling, because it's logarithmic.

Most people find arithmetic (the first number) easier. Once you're used to DIN, there's nothing in it.