Regards the ambient sensors, this information was passed from the
folks at Tekade.de on the DPReview forum when someone asked about
metering errors with their custom split-image prism viewfinder
screen. Just like the screen you bought, their screen works fine in M
and CW modes but needs a correction in S mode, for exactly the same
reasons.
For a TTL flash sensor to work, it has to be in the mirror box
(because it operates at exposure time). I doubt that Pentax would put
two different flash sensors in the body to support TTL and P-TTL
separately, so those are in the mirror box.
Godfrey
On Jan 5, 2006, at 4:34 PM, Don Sanderson wrote:
Godfrey, could you tell us where you found this info?
We were discussing it the other day, it would be nice
to have a reference source.
I know the older meters pretty well but the
technology has passed me up. ;-)
Thanks!
Don
-----Original Message-----
From: Godfrey DiGiorgi [mailto:[EMAIL PROTECTED]
Sent: Thursday, January 05, 2006 5:30 PM
To: [email protected]
Subject: Re: MicroPrism ist-D Focus Screen is here!
The Spot pattern sensor reads off the focusing screen and is not
exactly aligned with the optical center of the viewfinder optical
system, thus the metering discrepancy.
CW Averaging and Matrix meter patterns are read from sensors in the
bottom of the mirror box and should cause no discrepancy in meter
readings at all. I believe that the P-TTL/TTL flash sensors are co-
located with the CW Averaging and Matrix metering sensors.
(Far as I'm aware, this is correct information for D, DS, DS2 and DL
bodies.)
Godfrey
On Jan 5, 2006, at 2:17 PM, Don Sanderson wrote:
I tested with the spot pattern.
I'll try again with the others but the 1/2 stop really isn't
something I'm too worried about.
Which meter pattern are you using? Matrix, Spot or CW Averaging?
The new screen requires you to use -0.5 exposure compensation
to get the same meter readings as the original screen.
IOW the camera thinks the scene is 1/2 stop darker than it is
and will overexpose without compensation.
This would indicate the meter is behind the prism as others
thought and not behind the mirror as I thought.
Could you elaborate on that a bit? How does it increase
exposure? Does it
require a greater exposure time for the same results as the
original
screen, or less?
The new screen seems to increase exposure by about 1/2 stop.
