Originally posted by Mike Cash M lenses will only meter fully open in Av mode. But mechanically the lenses do stop down if you attempt to shoot with them in Av mode. Of course, the metering is all wrong so there's no point to it.
No the metering is not
all wrong. It is
right for the lens fully open! The point is that the exposure that you see in the VF is the one calculated for the
current aperture which is fully open. For my K100D, the camera uses this exposure (or one calculated in the same way) when it takes the photo. In Av mode, when the K100D sees that I have a K or M lens it basically gives up trying to work out what aperture I have set, and treats it as being fully open all the time. M42 lenses work in Av mode because the K100D does not open the diaphragm fully open (it cannot) so whatever aperture I set is treated by the camera as being "fully open".
Originally posted by Mike Cash You said the iris will stay fully open in Av mode, no matter what aperture is set on the aperture dial, and that is not the case.
Well I must have a faulty K100D because in Av mode if I set my M135 to f/16 and use the optical DOF preview the diaphragm stays fully open, but if I use M mode and use optical DOF the camera stops the lens down to f/16. (I have the appropriate custom menu setting.) Similarly, in Av mode if I set the M135 to f/16 the VF shows 1/180 (metering fully open) when I take a photo and look at the EXIF the shutter speed is given as 1/180, so the camera
did not stop down before taking the photo. However, if I use M mode, the camera
does stop down before taking the photo, but I have to make sure that I use the AE-L button before so that the camera meters at the specified aperture and calculates the shutter accordingly (in this case 1/4).
This is how my K100D works, is it faulty?
Richard