Calculate netural density filter

Is there a way to calculate how much a given density (say 0.9) the filter will affect the parameters?

Say I am shooting at ISO 80, f/8 and the correct shutter would be 5", if I then use the filter how much would the shutter speed change with the other parameters remaining the same?

Or should this question be stated another way?

If there is a way to calculate this I would be intersted to learn.

In the world of neutral density filters, the .3 filter eats up 1 "stop" of light, the .6 eats 2 stops and .9 eats 3 stops. In your example, 5" = 5 seconds? If so, then 10 seconds for the .3 filter, 20 seconds for the .6 and 40 for the .9 filter.

This any help?

othomas wrote in post #11794613
This any help?

Exactly what I was looking for, thanks!