Camera Ground Glass as extinction meter

I pulled out my very old 1959 Kodak Master Photoguide as I wanted to see if it had a filter factor calculator. It lists the factors but does not have a calculator. What I did find was a section that says to use a ground glass as an extinction meter to focus on the area with the important shadow detail, with black cloth on, open the lens all the way open and start to stop the lens until shadow detail is barely disitinquishable. There is table that says with Trix if at F8 then 16 secondes at F16. other end of the scale if at F64 then 1/10 of second at F8. Anyone ever tried this?

No, never heard of that! I'll have to dig through my collection of Kodak Master Guides to see if one goes that far back!

It is an interesting "rule of thumb" concept that could prove valuable in a pinch...

...even if that technique worked, you have the uncertainty added by the re-working of ASA value of film which took place after 1959 data guide, in 1960....

The only film is listed is TriX, my Masterguide same date lists Trix at 400 ASA. Shooting a 100 speed film like Tmax 100, then 16 seconds at F 8. Next time I shoot my 4X5 I might test against my Gossen.