Nathan - I asked the nice folks at Minox Processing Labs this question when
I got my III-s. They told me that the orange filter is a half-stop and the
green filter is a full stop. I haven't tested this exhaustively, although
I've kept it in mind for occasions when I'm using 100-speed b/w in very
bright sun - too bright for 1/1000 at 3.5. I have tried the filters, though:
the orange enhances clouds nicely and the green lightens foliage and darkens
most other things, e.g., facial features.

Okay, guys - am I wrong about these factors? - MSG

=========================================================================
Date: Fri, 6 Dec 1996 18:06:58 -0500
Reply-To: The Subminiature Photography Mailing List
<SUBMINI-L@LISTSERV.AOL.COM>
Sender: The Subminiature Photography Mailing List
<SUBMINI-L@LISTSERV.AOL.COM>
From: peter zimmerman <peterz@E....>
Subject: Minox Filter Factors
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"

Minox green and orange filters found on the III=series had filter factors of
2x (green) and 3x-4x (orange) depending on the red sensitivity of the film.

At the end of the III run the orange filter was replaced with a 10x ND
filter. NOTE: if anybody has such a IIIS and wants to sell it, LET ME KNOW!

The B had a 2x green and several different values of ND: 10x, 8x, and near
the end of the run, 4x. You can't trust a generic instruction book on this
point because you would have to know that the instruction book was the book
packed with a specific camera. And I do not have dates/serial numbers for
the different filter factors. BUT, in any event, the camera's meter takes
care of the factor for outdoor pix and flash is inherently so hard to do at
close range (front-to-back fall-off is severe), that guessing at 4x or 10x
will do fine. You can find out what your factor is by switching the filter
in and out and seeing how much YOUR meter changes, and can then use that
with your flash. But you'll have to do it out of doors in sunlight in order
to have enough meter range to make the measurement cleanly.

If MPL said that the orange filter was 2x, they are sadly mistaken!

The newer cameras have only an ND filter with a factor of 4x.

Pete Z
=========================================================================