Is it used at the negative stage then? I thought it was perhaps for calibrating some sort of exposure meter at the paper/easel stage. I suppose I would find this helpful in focusing 4x5 negatives with less obvious grain.
Thanks for clearing that up.
Tom, on Point Pelee, Canada
Ansel Adams had the Zone System... I'm working on the points system. First I points it here, and then I points it there...
I think it was popular up to '70 when grain focusers took main stage on that front. Yes, you put it instead of regular negative, focus and then replace it with regular one. Maybe they will be still useful for mural projections without extremely long arms. But I will be afraid to move negative carrier after precise focusing. Have one similar of SSSR origin.
It might be useful for checking enlarger alignment.
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2