Originally posted by Nass Had to google transilluminator and yeah, good call too. fyi a transilluminator is a lighting platform from underneath that you sit your thing on
Yes, it's similar to the white table we, old guys, were using to look at negative sheets. It's been many years since I had to document petri dishes but it's the standard way it's done. Not only for petri dishes, but for anything on/in a transparent/semi-transparent media or matrix.
For petri dishes, the additional advantage is that colonies (the things growing on the media) usually are more or less opaque relative to the media and back lighting thus greatly increase the constrast. They really stands out against the background, similar to a high key background. Obviouly, we're not talking here of doing an artitstic picture. But for documenting, it's fine and very reproducible. You can even find commercial scientific imagery system based on this...
The other "classical way" is to put the dishes on a black background and illuminate them with two light sources positioned each side on the lens, picture taken from the top. It's about the same idea as doing a macro with two flashes, but not macro... This also works well but one usually need to use a dedicated system for this kind of picture.