Originally posted by Docrwm Thanks folks. Based on this input I won an "A" auction instead of an "M" auction and came out cheaper too!
Good for you! Actually, having the "A" feature is an advantage in many ways. The better action of the "M" version aperture ring is moot, because it is completely unnecessary to take the ring off of "A". In fact not only is there no advantage, there are many disadvantages. Of course as most of us know, there are many control features and other camera features not available when using the ring. But also, electronic control of aperture via the camera body has its own advantages. I have the "F" version, which has AF and also the "A" setting on the ring. From the specs, the "M", the "A", the "F", and the "FA" all seem to have the same optical formula.
---------- Post added 11-14-18 at 06:13 PM ----------
Originally posted by clem I have used my M 50 1.7 lens since I bought it in the 70’s and there are firm clicks between stops. I have never heard about a problem before and I’m not going to worry about it now. The reason I like M over A is because I like picking the aperture instead of letting the camera do it automatically. I feel more in control of the outcome especially when it becomes a 35 mm equivalent of a 70 mm lens, perfect for portraits.
When not using the aperture ring, but having the "A" setting, with a camera body having electronic control of aperture via on-body controls, you can still select your apertures manually instead of the camera doing the selecting. Newer lenses don't even have an aperture ring at all. This came about back in the film era. Electronic implementation controlling aperture proved to have better exposure accuracy at certain settings, in the case of many camera bodies, over mechanical aperture control. Even true where the body could function either way. Back then, test reviews of both camera bodies and lenses often included exposure accuracy.
Your 50mm equivalent is more like a 75mm lens with a Pentax DSLR having the APS-C format. Actually, if I remember right, with Pentax it is 1.53 x which would put it at 76.5, quite close to the FA 77mm Limited on a 35mm film body.
In addition, when using a variable-aperture zoom lens, which most are, with the mechanical control, the aperture value will actually change as the lens is zoomed, no matter where you set your aperture. if you set f/5.6 it might well become f/9.5 or even f/11! With the electronic control, however, if you select f/5.6 it will stay at that value even when the lens is zoomed, unless the lens's wide open maximum is not that wide, like f/6.3 at the long end. Of course, if shooting in Av mode, the camera will alter shutter speed to preserve the exposure value, but that may not be what you'd rather have. Electronic control is even more advantageous in manual mode, so you don't have to continuously manually compensate for such change as you zoom.