Topic: Good length?


I'm new to media slideshows and would like some basic information to help me get started.

What would be a good length in time of a show? Not too long, or too short so that the viewer won't get bored.

About how many photos would that be?

My slideshows would basically fall into three categories:

1) Introducing a product: car, billiard training device

2) Introducing an Asian supplier/factory

3) For the family, like child birthdays.

I understand that a great slideshow depends on many factors, but I'm looking for a good starting point.

Thanks in advance,