ND Calculation Help - ISO 3 & Flash

[Leave Me Here]

Dear LF world -

Quick question, would just like some help to confirm the below..

Project-
Shooting 8x10 Paper Negs Portraits, 600mm f9 @ ISO 3, with Flash.

However, would like to preview on digital before hand, WITHOUT altering flash strength.

At ISO 100 on the digital, I think I require a 5 Stop ND filter to make it the equivalent of ISO 3?
Is that correct??

Then lets say, due to bellows compensation factor, I need an extra stop exposure, I would then need an extra ND stop? Making the equiv ISO 1.6?

Any comments would be much appreciated!

Thanks!
Matt

 

[Dan Fromm]

Count on your fingers. 100, 50, 25, 12.5, 6.25, 3.125, 1.5626, ... 0, -1, -2, -3, -4, -5, -6

 

[RalphLambrecht]

5 stops from ISO100 to ISO3(100 50 25 12.5 6 3)is confirmed.