Quote Originally Posted by Laurent View Post
I'd like to start tray development for my 4x5 negatives, but the question of the timer prevents me of doing so at the moment.

So, is there an Android timer that would be safe for this usage ?
I'm afraid I'd have to give that a big, fat, ugly NO.

Reason being: Any smartphone will be using a backlight which has spectral emission in the range of sensitivity of modern films. Even orthochromatic film may be fogged. The backlight leaks badly, even with a black screen.

When it comes right down to it, what you will need is an audio cue. Since you're going to be working in total darkness, the only thing you'll be able to use is something which yells at you. There exist darkroom timers that can do this. It is also quite possible to build one yourself.

At a more primitive level, a wall clock with an audible tick will work. I use this for print processing.

Quote Originally Posted by Laurent View Post
I installed "Darkroom timer" http://www.android-software.fr/darkroom-timer, which seems nice, but am not sure about the effects on the negative.
I use this on my Galaxy Tab when processing film in a daylight tank. Quite convenient, though it's missing features I would like. The timer I used as a kid was my father's Vivitar Process Commander, which allowed me to set drain time, agitation interval, agitation time, and all sorts of other stuff. It was also quite usable for print exposure management. Man, do I ever miss that thing. Maybe one of these days I'll build something similar.

Good luck in your endeavors!