“I want to make contrast masks from 6×7 [120 film] color. What film and developer should I use. I can’t afford 4×5 Tmax100”
First: don’t use 4×5 size film. Use 120 film, cut into 3 inch length.
Next: it must be panchromatic film to collect (mask) all the colors on your original without being a separated mask.
Use Ilford PanF film. Ilford PQ Universal developer. Arrange the stack as illustrated. Set the enlarger as if you were making an 11×14 print using your suggested lens. Follow the start points indicted in the drawing.
The black paper underneath is more important than you may think. It controls reflected light and flare back toward the cover glass and lens.
PQ developer 1:20 for 3minutes continuous agitation 68degrees F.
The darkroom has been the recipient of electronic gadgets for decades. Many of the private darkrooms were equipped with electronic aids long before the digital upgrades. The intent was convenience, as well as ease of operation for the casual darkroom printer.
The first items were timers. After that came analyzers – darkroom meters used for judging exposure and contrast selection.
Enlarger timers, usually, control time. First ones were mechanical, much like a clock. Digital timers provided more features, including “f-stop” timing. In wet room (side) are process timers; some are multi-step, or even multi-process capable.
Exposure/ Contrast Meters
Technically they are on-easel meters. The readings are taken at the printing stage. The negative is projected onto the easel; the meter probe (sensor) is positioned on the easel to capture the light from a spot of the image.
Darkroom 21: Tron
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Published source, DIY build information: timers, light sources, meters