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. I haven't compared the results with the new/original screens using TTL/PTTL flash yet. I assume it would have no effect on TTL but may on PTTL. In PTTL the preflash is before the mirror goes up and the main flash is after. This is evident from the fact that you can see the preflash thru the viewfinder.
BTW: Having this screen makes it _very_ obvious just how inaccurate AF can be sometimes. Makes the DA lenses focus clutch seem even more valuable for "touch-ups". Don > -----Original Message----- > From: Shel Belinkoff [mailto:[EMAIL PROTECTED] > Sent: Thursday, January 05, 2006 2:39 AM > To: [email protected] > Subject: RE: MicroPrism ist-D Focus Screen is here! > > > 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 focus looks pretty good on the pics you posted .... > > Shel > > > > > [Original Message] > > From: Don Sanderson > > > http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7573618765 > > > > Here are the focus accuracy results using the microprism center: > > > > http://www.donsauction.com/pdml/istD_FocusScreen.htm > > > > This is with a Sigma 50/2.8 macro wide open, focus point was the > > highlight in the top birdies eyeball, manual focus. > > Seems absolutely spot on to me, though the screen seems a bit > > less bright than the original, focusing was very easy, the > > microprism effect was quite pronounced. > > > > Autofocus seems to not be affected in any way. > > > > The new screen seems to increase exposure by about 1/2 stop. > > > > All in all, a good $30.00 spent for a focus challenged person > > such as myself. ;-) > > > > One Caution: The new screen is a bit thicker so it loads the > > springs on the closed retainer frame a bit more. > > When you release it, be ready to catch it as it pops out! > >
