[rollei_list] Re: Hello (again), new Rollei TLR

Richard,

I am not surprised at your statement, I am ASTOUNDED!
At one time I compared all my Weston meters, to a Luna
Pro.  All the Westons had been checked out by QLM.
They were in agreement after the corrected film speeds
were used (Weston vs. ASA) The Westons ranged from
the pre-Master 650 to the Euromaster II, except for that
POS Master 6 (Japanese made toy)

Jerry

Richard Knoppow wrote:

> ----- Original Message -----
> From: "Jerry Lehrer" <jerryleh@xxxxxxxxxxx>
> To: <rollei_list@xxxxxxxxxxxxx>
> Sent: Friday, April 29, 2005 4:32 PM
> Subject: [rollei_list] Re: Hello (again), new Rollei TLR
>
> > Richard,
> >
> > I have been using Weston meters since before you were
> > born, and I did not have under exposures when I used
> > the meter correctly.  I have used Weston, ASA, DIN and
> > Scheiner speeds with the corresponding dials.
> >
> > The first Weston meter I used was in 1936, and it was spot
> > on
> > when I sold it this year.
> >
> > Jerry
> >
>    Check the Weston against another refleced light meter on
> a large flat surface. A gray card is not necessary because
> one is only comparing the two meters for a given amount of
> light. Laying them on the surface of a light table also
> works. You will find that the Weston will give you shorter
> exposures when the speed setting is made to the "equivalent"
> ISO speed. This is the next lower number on the Weston
> scale. When the original ASA system was in use this worked
> fine because that system had a 2.5 times fudge factor built
> in.
>    I was somewhat surprized at this myself but have found it
> consistent on several Weston meters which are calibrated in
> Weston speeds.
>    It is interesting to compare the Kodak speeds with Weston
> speeds. Kodak speeds were measured using the minimum
> gradient method of L.A.Jones and later adopted by the ASA
> but with the addition of the fudge factor. Kodak Speeds are
> approximately double the current ISO speeds and were about 4
> times the old ASA speeds (with safety factor). Here is a
> comparison of some film speeds as given in c.1944 Kodak
> literature:
>
> Film          Kodak     Weston
> Plus-X        250        50
> Portrait Pan  200        40
> Tri-X         800        160
>
>     Weston speeds may not be exactly a factor of 5X from
> Kodak speeds because Weston also classified speeds by
> groups.
>
>     The Weston speeds were determined by making a D-Log10E
> curve of film developed to a a gamma typical for the film.
> The measurement point was the log exposure point at which
> the density was equal to the gamma, i.e., for a gamma of 0.7
> the speed point is measured at a density of 0.7.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
>
> ---
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