Vic Mortelmans wrote: > Hi, > > OK, obviously I do know that A-lenses have an A-modus, allowing the > camera to set the aperture (shutter-priority modes), while M-lenses > always require the aperture to be set on the lens. > > But being in persuit of a 50mm f/1.4, I notice that the A-model is > priced at least twice as high as the M-model, if not more. > > Looking at the mechanics of the diaphragma, I wonder if an A-lens is > that different, apart from the electronic contact that probably doesn't > do anything more than telling the camera whether the A-mode is on or off. > > And I also assume that the 50mm f/1.4 M and A are optically identical? > > So is there any objective reason for the price difference, or is it just > the game of demand and available quantity that sets the price? > > Groeten, > Vic >
There's two basic differences. The first is the A mode & contacts, the second is that A lenses have a fully linear aperture actuation. Only one M or K lens has a fully linear aperture and that is the second version of the M 28/2.8, which is fact the A design with an M mount on it (Pentax ran out of parts for the earlier version prior to the launch of the A series lenses, so they did a run of A 28/2.8's with a pre-A mount and M lettering). A fully linear aperture is necessary for the camera to be able to accurately set aperture in P and Tv modes. There are a few cameras which can do that without a linear aperture (the Chinon CP-6 and Nikon FA are two) but they double check and adjust exposure after the lens is stopped down. -Adam -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
