Originally posted by Styx1284 - How hard is it to use the m42/K mount. How long (minutes,seconds...) does it take you generally to put it/take it off your camera?
m42 lenses have a long thread, so there is a fair bit of (un)winding to mount/remove them. The genuine Pentax adapter takes seconds to remove, but you need a free hand (so swapping a m42 and k-mount lens is slightly longer than just two k-mount lenses). But practice speeds things up.
Originally posted by Styx1284 - Would it be possible to just leave the mount on the lens?
It requires some modification, but its possible. There are threads about this, I think.
Originally posted by Styx1284 - How trustworthy are the 3rd party M42/K-mount adapters that we find on ebay
impossible to answer, there are too many unbranded adapters with undocumented differences. Some are great, others are a nightmare. Best to order something someone already tried,
Originally posted by Styx1284 smc Pentax M,A,F,FA
K and M are oldest. Camera can stop them down, but you need to select the aperture on the lens, by hand. You need to input focal length manually. Can only shoot in M mode and Av mode (but Av is always wide open). Stop down metering with green-button.
A lenses have auto-aperture. This means there is an A setting on the aperture ring, which lets you control the aperture from the camera body. This also unlocks Av and other modes. Continuous auto metering.
F and FA lenses are newer, they have AF and are basically fully automatic, but they still have aperture ring and such things.
DA are newest, which are the most automatic and they don't have aperture ring and often don't even have distance scales.