Originally posted by Ahsaaan
My lense is Manual smc M 1.7 the problem is i cant change aperture mechanically when attached to camera something inside is keeping it wide open whereas when ever i detach lense and change aperture of lense from ring it changes.
Welcome to the Pentax Forums!
That is how lenses with auto aperture actuation work.* Most (almost all) K-mount lens when used on a K-mount camera only stop down for the exposure, depth of field preview, or for stop-down metering. When using the aperture ring to control the iris, this is only allowed in M or B modes on your camera with metering limited to M mode with set ISO. One must also enable aperture ring in the menu settings. Basic instructions are on p115 of the user guide. All other modes operate as Av mode with the lens staying wide open, even during exposure.
Steve
* Since the early-to-mid 1960s, the vast majority of SLR lenses (all makes) work this way with very few having fully manual aperture.