Quote Originally Posted by MattKing View Post
If you are adjusting shutter speeds, you multiply.

If you are adjusting apertures, you add the base 2 logs of them to get the change in stops.

The base 2 logs are the number you "raise" 2 to to get your factor. And they are the stop equivalent of the factor.

Here is a calculator: http://www.miniwebtool.com/log-base-2-calculator/

so for your factor numbers 2.15 and 2.5 the result is 1.1 + 1.3 = 2.4 stops (after rounding off).
Thanks for helping me understand this.

So for 1 sec at f4:

Adjusting shutter speed it's 1 x 2.15 x 2.5 = 5.375 sec (adjusted for RF) at f4.

Adjusting aperture it's 1 sec at f4 + 1.1 + 1.3 = roughly f1.8 (2.4 stops).

Or my original exposure becomes effectively 1 sec at roughly f9.

Do I have that correct yet?