Day/artificial light - different ISO?

[kully]

I have a 1000ft roll of HP5+, on the outside it says ISO400 for daylight and ISO200 for incandecent/(tungsten?).

Thinking about a post I read a few weeks ago on photo film's different sensitivities to different wavelengths of light, I was wondering whether ISO should be adjusted for different light sources. Not just with HP5+ but with other films too.

Or. Is this the ISO with the correct filter on (filter factor)?

I've not had any problems I've known to notice, just curious.

EDIT: Actually, I did have problems with under-exposure when I was using APX400 last year, but I can't be sure whether it was my crappy metering or this.

cheers,
kully

 

[Doug]

It's true that, to various degrees, films are less sensitive to reddish light than the meters. So the meters turn out "optimistic" exposure suggestions, and you end up with thin negs. This would affect use of the stronger orange and red filters too.

Ilford does (or used to) publish the sensitivity curves for their films, and I note that XP2 suffers this discrepancy less than the traditional B&W films.

So, yeah, try following Ilford's ISO suggestions and see how it works for you!