View Full Version : Calculating low ISO

Glen Seelenbrandt
4-Jan-2016, 20:21
I have been playing around with Liquid Light and Ag Plus on glass and tintype with the goal of working towards making my own emulsions. Ag Plus is said to have an ISO of around 1. I'm a little confused as to how to calculate proper exposure for this using my light meter. I know that each stop down usually half that above it e.g.: ISO 100 is one stop below ISO 200. My Minolta iVF goes down to ISO 3 which looks to be 1 stop below ISO 6 and 2 stops below ISO 12. Is ISO 1 considered to be one stop below ISO 3? or is it 2/3 stop below ISO 3? Do I need to shoot for somewhere between ISO 1.5 and ISO 0.75?

Glen Seelenbrandt
4-Jan-2016, 20:59
I think I figured it out...it looks like 1 is actually 5/3 stops below 3. Looks like it goes 3,2.5, 2, 1.6, 1.2 and then 1. Can anyone confirm this? Thanks!

5-Jan-2016, 02:05
Half the iso is double the exposure. Iso 1.5 is one stop slower than 3, iso 0.75 is two stops below 3. So iso 1 is roughly 1 2/3 stops slower than 3.