This is one way to control the amount of light reaching the film. TTL metering is electronically controling the flash with sensors built into the camera. This can control both timing and intensity of the strobe as well as the shutter speed. Film speed refers to the sensitivity to light for a certain film. A film speed of 400 will require less light to atain proper exposure than say film with a 100 asa rating.
Faster films are more likely to become grainy when enlargements are made.
Colour absorbtion is caused by the water filtering the light spectrum. The first colours to be absorbed are the reds and oranges, the last are blues and greens. When shooting 10 feet from your subject the light from the flash travels 20 feet before reaching the film. Parallax correction is required when shooting close-up photographs with a viewfinder camera. The adjustment corrects for the difference between what the lense sees annd what the viewfider shows.