Quote Originally Posted by Terry Again View Post
That said I must ask where the formula came from to make the adjustment of the camera setting for film speed?
I recalibrate the ISO setting as follows.

Bright sunny day, ISO 100 film, we all know the setting will be f16 at 1/125th.

I insert a 1.5v battery in place of the required 1.35v battery.

Adjust your meter setting to see which ISO setting tells you to shoot at f16 @ 1/125th.

In most cases I have found a setting of ISO 25 at 1.5v equals a setting of ISO 100 using 1.35v.