What is the purpose of this formula
I have been playing with my meter(not rudely of course) and I can't figure something out.
In the ZOne System adams used a spot meter to get his readings. He metered the important low and the important high. The difference between the two was the range. A normal range, for adams was 5 stops. Zone 3 to 8. Now The BTZS guy used an incident meter to do the same thing. If you tried to use a spot meter for his system you had to do a formula thingy that boils down to Meter difference +5.
While playing with my meter I realized that with the Spot attachment I was getting maybe a difference of .3 stop more light than with the incident part. I went to get the trusty old luna pro and got the same incident reading. SO why the hell do I have to go through some obnoxious formula when I use the spot meter? on the flip side is there something wrong with my meters if the spot part and the incident part is so close together? Since I used two seperate meters and came up with the same difference I doubt it.
Three tenths of a stop is not going to make that big a difference, especially in B/W. And it sure does not warrant adding five to the range.
Did I read BTZS wrong