NedL
Subscriber
Hi Doremus,
There is, as you say, also a red component to the general problem. But the OP question centered around darkening skies. The cited film suggests using a yellow filter to achieve this not a red one.
Sorry but I stand firm orthopanchromatic is a made up term. It was dreamed up to explain faulty sensitization of Efke films some years ago toward the red end of the spectrum to make a problem seem a feature. (As I pointed out these sensitization dyes are hard to synthesis and thus expensive. The bottom line triumphs over quality.) Find the term in Haist and I will give the matter another thought. Unfortunately marketing departments now write documentation not scientists. Does the term say anything meaningful? Is the film more ortho than panchromatic or vice versa? We don't know. Looking at the sensitivity curve Acros could just as well be called "isopanchromatic" having reduced blue sensitivity and higher yellow.
Jerry
Good point. "Isopanchromatic" actually seems to describe what I like about this film better. I like to use it without a filter, and it reminds me of using a light yellow filter with other films, but with more "separation" between different shades of green. By the way, the term "orthopan" has been bandied about by Adox with regard to their CHS II and if you look at the sensitivity curves it is also "isopan"
