[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Rollei] Meter calibration...

At 10:08 PM 11/3/2002 -0500, you wrote:
>At 06:37 PM 11/3/02 -0800, Don Williams wrote:
>* f3.5 is a "ringer", just about in the middle of f2.8 and f4.  I don't 
>know why they picked that as a standard, unless it represented some sort 
>of technical limit in olden  days.  There are a couple of "ringers" which 
>come up from time to time, typically about a half-stop from the standards, 
>again probably based on design limitations.
>Well, f/3.5 is ringer in more than one sense.  There is that other 
>aperture scale, 1/3 off of the one you gave, and commonly known as the 
>"European" scale:

Never heard of any European scale, just ASA.

Let me square these and see what the relationships are:

>F       F-squared       Next Ratio
>1.2     1.44
>1.5     2.25            1.56
>2.3     5.29            2.35
>3       9               1.70
>4.5     20.25           2.25
>6       36              1.78
>9       81              2.25
>12      144             1.78
>18      324             2.25

The column "Next Ratio" should be the same in each instance since it 
represents the relationship from one F number to the next.  In the ASA 
scale it's always 2.  I must have made some math errors, but in any case it 
just doesn't make sense to me.

(Yes, we should be using squares of the reciprocals, but it doesn't affect 
the pattern we are looking for.)  This pattern I don't understand.

>Note that f/3.5 doesn't fit into this one, either.  Leitz and most other 
>German makers used this scale until about 1960, Zeiss being the one firm 
>which almost always (I belive that the known exceptions are well under a 
>hundred in number during the entire last century) used the American scale 
>you gave.

Does this mean that the old Leicas should have f-stop settings of 1.2, 1.5, 
2.3, 3, 4.5, 6, 9, 12, and 18?

>msmall    FAX:  +276/343-7315
>Cha robh bàs fir gun ghràs fir!

     Don Williams
     La Jolla, CA