Orthochromatic photographs are taken with Orthochromatic film which is very sensive to colours from blue to green but extremely insensitive to colours from red to orange. It's usually used for copying videos in a darkroom with red light because the film does not absorb any red.
1. Open the image for editing.
2. Add a "Hue/Saturation" adjustment layer (Layer> New Adjustment Layer> Hue/Saturation. Apply the following to the "Reds":
Lightness: -100
3. Apply the following to the "Yellows":
Saturation: 50
Lightness: -25
4. Apply the following to the "Greens":
Greens: 75
Lightness: -25
5. Apply the following to the "Blues":
Saturation: 75
Lightness: -25
6. Apply the following to the "Magentas":
Lightness: -25
7. Apply the following to the "Master":
Saturation: -100
Orthochromatic Film
Regular Black and White Film
8. Compare the differences between the orthochromatic and the regular black and white film.