Posted by Mal Stone on January 06, 2001 at 13:49:53:
In Reply to: Bellows factor posted by Morris on January 05, 2001 at 05:04:38:: I'm trying to understand the procedure in laymans
: terms about adjusting for the bellows factor after an
: exposure reading is done.
: I would appreciate any (if possible) simpler
: explantion.
I taught as a lecturer in photography here in the UK.
Bellows factor was always a chore for the students to
calculate.
We found a very simple way using a ruler.
Firstly you need to convert the lens size from millimetres to
inches i.e. a 150mm lens = 6 inches, 180mm lens = 7 inches
etc.
Next step you measure the distance from the film plane to the lens
centre (again in inches)
You then read the inches as F stops (a 6" lens as F6 - 7" lens as
F7)
If you read the F stop increments on a Weston meter or any meter
that shows numbered 1/3 stop increments you can easily equate
bellows factor.
Say we have a 7" lens and a bellows extension measurement of 9" we
then take the bellows factor as 2/3rds of a stop (F7 - F8 -
F9)
An 8" lens with a 12" extension would be 1and a 1/3 stops (F8 - F9
-F10 -F11 -F12)
Hope I've been of help!