I may well be telling you something you already know, but it was a realisation for me (not so much a discovery, as a 'connect the dots').

I'd been having all sorts of problems trying to use IDL for indoor scenes where the room only had a smallish window. Previous threads spoke of compensating for Poser's lack of camera settings (aperture and exposure settings) by cranking up the lighting. I tried that, but it was always too dark.

Anyway, I got to thinking about using a genuine SLR camera to photograph the room in my scene, and what setting I might use. If I was to use 100 ASA film with a nominal aperture of f4 or so, I'd expect an outdoor shot in full sunlight to have an exposure time of about 1/60th to 1/125th of a second. Using those same settings in a room like that in my scene, I'd expect the exposure time to be about 1 to 2 seconds.

Applying that rule of thumb, and knowing that every increase in the time roughly doubles the amount of light, I counted up the steps (1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1... 7 steps) then doubled the light the same amount: 100, 200, 400, 800, 1600, 3200, 6400. That's right, set the light of the sun to %6400!

Then the skydome. Same counting, set ambient to match. Ambient to 64!

I rendered it, and it worked! A but dull still, but within expectations. I 'bracketed' one stop up (light to 10,000, ambient to 128), and got the image above...

Basically it means I can apply general rules for a camera to estimate values for light in IDL. Still not as good a result I might expect if there were genuine exposure controls in Firefly, but a big improvement over what I'd been getting.

Hope this is of use to someone!