Fumbling towards a correct exposure for Dry Plates

[RLangham]

Thanks, and the rest of your post is an excellent explanation of the Sunny sixteen rule.

ISO below 1? Fifteen years ago, I took a Daguerreotype workshop with Jerry Spagnoli at the Photogrpaher's Formulary in Montana. The exposures were something like 30 seconds wide open at f/5.6 in sun or overcast. I started counting backwards and came up with an equivalent "ISO" on the order of 0.005 or something equally useless . . .but it was interesting to do. The sensitized Dag plates were so blue sensitive that UV penetrating the overcast was effective in exposing the plates. . . .so any direct comparison to film was not useful.

Yes, I wouldn't want to get my portrait taken with a Dag!