Re: Convert camera meter to incident meter?

On Mon, 03 Oct 2005 21:26:08 -0400, McLeod <cerveza@xxxxxxxxxxxx>
wrote:



>I decided to do a little test right here at my computer since
>everything you were saying went against everything I was taught and
>have been teaching for the last 3 years. I took out a Kodak grey
>card, my Minolta IV meter, and my Gossen Lunasix F meter.
>I placed the grey card right beside my keyboard, grey side up. My
>lighting in my office is dim so I set both meters to ISO 1000.
>
>I first took an incident reading with the Minolta laying flat against
>the card with the dome up and got 1 second at 5.6 plus .6 of a stop.
>I then put on the reflected attachment which takes a 30 degree FOV. I
>aimed the meter at the card from about 7-8" away and got a reading of
>1 sec at 5.6 plus .7 of a stop.
>
>I then held the Gossen meter upright so the dome was aiming straight
>up on the same plane as the card. I got a reading of 1 sec at 5.6
>plus 5/6 of a stop. (The Gossen only has markings at 1/3 of a stop
>but it was exactly halfway in between) I then slid the dome over and
>pointed it at the grey card at almost exactly the same position as the
>Minolta reflected reading. I took a reading and got 1 sec at 5.6 plus
>2/3 of a stop.
>
>What you are saying does not make sense and can be proved by anyone
>with a grey card and a meter.
>
First off.. was the lighting even?? Second..You did right with
incident measurement however 7-8 inches is too close to get an
accurate reflected measurement based on your 30 degree FOV. You only
measured the light on a small part of the card therefore it cannot be
correct. You have to measure the same FOV in both tests...otherwise
you are doing nothing more than a spot meter reading.

In addition low light is not an accurate way to test. You need enough
even lighting to get medium speed measurements.

I conducted the same test as you with both my Minolta Autometer and
Weston Ranger 9 taking into consideration FOV of each meter (10 degree
for the Minolta and 18 degree for the Weston) and used a 500w tungston
light set 4ft from the card to give even lighting.
Minolta:
1/125th f/8 incident
1/125th f/16 reflected
Both reading with the Minolta were just slightly on the high side of
each full reading
Weston:
1/125th f/8 incident
1/125th f/16 reflected

The Ranger 9 was calibrated to factory specs back in June of this year
by QLM. The Minolta was sent back unadjusted with a note that it was
in spec..

--
Colyn Goodson

http://www.colyngoodson.com
.

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