The Holga's shutter speed
The Holgas shutter speed is around 1/100th of a second, although each Holga may be slightly different so the shutter speed is an approximation. Due to the way the Holgas shutter is made, it's entirely plausible that the shutter speed may change over time. This is due to the fact that the shutter mechanism consists of a simple spring-type piece of metal, which over time may loosen and cause slower shutter speeds.
But as you may have guessed by now Holgagraphy isn't an exact science by any stretch of the imagination. I'm just providing this information so you can expose your film by making educated guesses.
Long exposures
New type 'N' Holgas feature a bulb mode which allow you to keep the shutter open indefinitely. For long exposures you need to be aware of something called Reciprocity Failure - see the exposure section for more details.
