Originally posted by aleonx3 With M42 lens where there is A/M switch (some don't), you can use Av mode instead of M mode on the camera. With Av mode you can use EV to compensate for over/under exposure, with M mode, you can use stop-down metering (green button) but not EV change to augment exposure.
Re M42 Lenses and the A/M switch.
The A/M switch only exists on later M42 lenses, which allowed for wide open focusing but stopped down metering.
There are some M42 lenses with automatic aperture and no A/M swithc (I think) these are "auto takumars" in pentax's line up. These lenses will not stop down because the activation pin is not pressed, they need a simple modification to make them work in stopped down mode on a K Mount body. (any body film or otherwise)
There are also preset M42 lenses, where there are 2 aperture rings, one is usually stiff with defined detents for the aperture settings, the other quite loose and no detents. you preset where you want to shoot, and the loos ring acts as the stop down function when you are ready.
Re exposure compensation.
I can only speak here about the *istD, K10D and K7D (all I own) with the exception of the K10D where EV compensation
DOES NOT WORK in manual, EV compensation does work in manual mode for the other pentax cameras, this allows for compensation in both manual and AV mode for any errors introduced by the M42 lenses not shorting the lens mount pins