Metering for IMAGO direct positive paper with iPhone lightmeter app

[jonbrisbincreative]

I use a lightmeter app on my iPhone which I have found to be spot-on accurate for all the scenarios I've tried. I use it all the time with my RZ67. I bought some IMAGO direct positive paper from lomography.com and have experimented with it some with inconsistent results so far. I think part of the problem is that I have a hard calculating correct exposure from my iPhone app which only goes down to ISO 6.

I've found this direct positive paper to need about ISO 1.5 so I was wondering if there was a rule of thumb I can use to translate a reading for ISO 6 to the equivalent for ISO 1.5? Will I just have to keep a little chart in my pocket to help? :)

I'm also using the Arista paper from Freestyle cut down to 4x5. It has about ISO 3 or 4, though, so the times are radically different (seconds vs fractions of a second). Sadly, I don't remember what I loaded into my film holders last so I'll have to just burn those sheets and load fresh.

Is there a "sunny 16" rule for direct positive paper? What is your experience with it?

[photonsoup]

I preflashed Arista paper and expose it at ISO 12. I meter for 100, then add three stops. Seems to work OK with my iPhone app, spot meter, or digital camera.

[koraks]

I've found this direct positive paper to need about ISO 1.5 so I was wondering if there was a rule of thumb I can use to translate a reading for ISO 6 to the equivalent for ISO 1.5?
Just add two stops...

If your meter reads e.g. 0.5 seconds @ f/8 @ ISO6 then correct exposure for ISO1.5 will be 0.5 seconds @ f/4 or 2 seconds @f/8