Re: ATM Photographing foucalt/ronchi shadows

[astillma@nit.AirTouch.COM (Anthony Stillman)]

Tom,

I've used a 35mm SLR with a 50mm lens.  I use 1000 ASA film and expose
for between 5 and 10 seconds.  Oviously everything has to remain stable.
I've found that it really is no big deal though, I've even taped the
whole aperatus together and not used a shutter release and still gotten
decent results.

A brighter light source helps with exposure time, but they still tend to
be longer than a second.  Really fast mirrors are hard to read with a 
foucalt.  The contrast is too high.

Ronchis are a little easier as there is more light, here stability is
important or the line edges blur.

Focus on the mirror, not the screen, knife edge or wire.  You are imaging
a shadow iluminated by the mirror not the item making the shadow.

Place the lens about where you would place your eye.

A really dark room helps reduce the fogging.  I use my black bag to 
keep stray light from the source to a minimum.

Good luck
and please ask if you have any more questions.

Anthony