Whats done for convenience? Open apeture metering and AE? You bet it is! That's why stop down metering went away and why open apeture AE option is better than green button thingy is some situations. There is only one reason for stop down, its possibly more accurate, but if the open aperture design is such that the amount of error it produces compared to stop down method is small enough to be unnoticable, then the convenience of open aperture metering and AE far outweighs the slightly better but unneeded accuracy of stop down methods under certain bright light condtions.... In low light with small apeture settings, open aperture method is actually more accurate which totally kills any small advantage stop down method may have had. bottom line, nobody does stop down metering anymore for these simple reasons unless there has been a mount change that necessitates using stop down on some old incompatable mount. that is not the case with the Pentax DSLRS and K/M lenses though... JCO
-----Original Message----- From: Gonz [mailto:[EMAIL PROTECTED] Sent: Sunday, September 18, 2005 11:22 PM To: pentax-discuss@pdml.net Subject: Re: green button wars (again) J. C. O'Connell wrote: > > Secondly while its true stop down metering CAN BE more accurate in > sufficient light but if the tolerances of the lens apertures are kept > within design parameters and the cam sensor as well , the wide open > metering can work with more than enough accuracy for even narrow > latitude slide films. That is why the entire photo industry abandoned > stop down metering about 30 years ago. Think about this if stop down > meter is "better" than why doesn't the camera stop down meter with A, > F, and FA lenses too with no open aperture option? Its done for convenience. You can see your shutter speed real time and can make adjustments if its too fast/slow. Pentax could have had a pseudo-AE mode if they wanted to with just one press of the green button per aperture selection if they wanted to. By taking two measurements, one wide open, one with the aperture down, a simple ratio could be used for all future calculations using the future wide open measurement. If you changed the aperture, you pressed the green button again. rg
