3 ms·

It's because Wet Plate is typically orthochromatic.

galago 7y ago
michrassena's comment has it right. 'orthochromatic' was a later term implying that the film represented the 'correct' version of the spectrum, because it was more sensitive to blue light. the term 'panchromatic' was adopted when black and white films eventually approximated visual sensitivity. the history of this spans decades, which is why it can be confusing. by the late 20th century, 'ortho' meant a monochromatic film or printing paper that was not sensitive to red light, hence it could be handled in a darkroom with a red safe-lite. however, the spectral sensitivity of even standard photo paper today might be greater than the earliest emulsions.
- stan_rogers 7y ago
  "Orthochromatic" was a fix; it had extended green sensitivity compared to earlier processes/materials (which were usually referred to as "actinic" after ortho was introduced). Ortho was called ortho right from the beginning to distinguish it from what came before. The extended green sensitivity is what made it right. Or at least somewhat less wrong than things had been. If they'd found a way to create panchromatic plates/film before ortho as we know it happened, the name "orthochromatic" would have been given to that instead. So why did ortho rule the roost in the darkroom and in process photography when we had "actinic" papers around? (Obviously, panchromatic is out unless you like working in total darkness.) Incandescent lamps for exposure is a big part of the answer. You don't get a lot of blue light out of a glowing filament, and sunlight isn't quite as consistent and reliable as you might want it to be. (And arc lights aren't a lot of fun to work with or around.) Non-repro blue, a pale cyan that humans can easily distinguish but ortho film/paper can't, is most of the rest. Panchromatic can "see" non-repro blue by design, and "actinic" can see it because it's not blue enough to appear white if it's dark enough to see easily (in paste-up, etc.). Non-repro blue, ruby masks and relatively bright safelight made life... well, not exactly easy when compared to, say, a desktop publishing application, but it beat the heck out of constant squinting in the dark, wondering if that thing was really supposed to be there, or if it was a line at all.
  - staticautomatic 7y ago
    Developing film by inspection is a joy. I've developed a lot of ortho 4x5 under red safe light and love it even though I don't need to (my developer exhausts around the same time the film finishes developing so I don't actually need to inspect). I just do it for fun.

michrassena's comment has it right. 'orthochromatic' was a later term implying that the film represented the 'correct' version of the spectrum, because it was more sensitive to blue light. the term 'panchromatic' was adopted when black and white films eventually approximated visual sensitivity. the history of this spans decades, which is why it can be confusing. by the late 20th century, 'ortho' meant a monochromatic film or printing paper that was not sensitive to red light, hence it could be handled in a darkroom with a red safe-lite. however, the spectral sensitivity of even standard photo paper today might be greater than the earliest emulsions.

stan_rogers 7y ago
"Orthochromatic" was a fix; it had extended green sensitivity compared to earlier processes/materials (which were usually referred to as "actinic" after ortho was introduced). Ortho was called ortho right from the beginning to distinguish it from what came before. The extended green sensitivity is what made it right. Or at least somewhat less wrong than things had been. If they'd found a way to create panchromatic plates/film before ortho as we know it happened, the name "orthochromatic" would have been given to that instead. So why did ortho rule the roost in the darkroom and in process photography when we had "actinic" papers around? (Obviously, panchromatic is out unless you like working in total darkness.) Incandescent lamps for exposure is a big part of the answer. You don't get a lot of blue light out of a glowing filament, and sunlight isn't quite as consistent and reliable as you might want it to be. (And arc lights aren't a lot of fun to work with or around.) Non-repro blue, a pale cyan that humans can easily distinguish but ortho film/paper can't, is most of the rest. Panchromatic can "see" non-repro blue by design, and "actinic" can see it because it's not blue enough to appear white if it's dark enough to see easily (in paste-up, etc.). Non-repro blue, ruby masks and relatively bright safelight made life... well, not exactly easy when compared to, say, a desktop publishing application, but it beat the heck out of constant squinting in the dark, wondering if that thing was really supposed to be there, or if it was a line at all.
- staticautomatic 7y ago
  Developing film by inspection is a joy. I've developed a lot of ortho 4x5 under red safe light and love it even though I don't need to (my developer exhausts around the same time the film finishes developing so I don't actually need to inspect). I just do it for fun.