Determing exposure time

On: Sun, Apr 14, 02 04:58:44 PM

Thilo K. wrote:

If I make some strip exposures with different exposure times, I will still influence the final result by increasing or waning development time until density is about 1.0 for transmission holograms. So I canīt be sure whether it was the wrong exposure time or the wrong development time that was responsible for a over or underexposure... How did you cope with that problem ?


Tom B. - Mon, May 20, 02 04:48:47 AM

It's the brightness of the finished hologram that matters. You want to find the optimum combination of exposure and development time. Using a relatively flat object that fills the frame (say 4 by 5 inches), you could expose a sheet of film as one big test strip, exposure time increasing across the frame, then cut the film into strips and develop each strip for different periods. The brightest image wins. You will need to find a way to mark the strips so you can tell which was which afterwards - permanent marker pen ink gets eaten by the developer - maybe a crayon or china marker, or notching the edges? If you are using plates, you might want to make a thin vertical developing tank so you can lower the plate into the developer one step at a time.

Thilo K. - Mon, May 20, 02 12:43:35 PM

Iīve heard this suggestion multiple times yet. But I came to the conclusion that it canīt be the best method: Just consider what happens if youīre using no disposable developer for single use, if youīre using a developer with waning quality ? Or even if youīre using a one-time developer, what if the temperature of it changes ? What if your laserīs power changes due to its age ? What if your films/plates loose momentum of their sensitivity due to their age ? You wonīt be able to reuse the values you get with the test exposures. I donīt know how to do better, but I donīt think that is the real thing.

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