On Sun, 17 Dec 2006 19:00:50 +0100, John Francis <[EMAIL PROTECTED]> wrote:
> On Sun, Dec 17, 2006 at 10:00:10AM +0100, Jens Bladt wrote: >> But there are contacts on the Adaptall 2 mount for Pentax. >> This will fit any Pentax KA bayonet and report the aperture setting to >> the >> camera, which will work like any A-lens. > > While there are contacts on the Adaptall 2 mount, they don't actually > report the maximum aperture of the lens, because there's no way for the > lens to communicate this information to the adapter. Instead they There are two mechanical links beteen lens and adapter. One of this could convey maximum, and the other current aperture... > always report the same maximum aperture (f2.8), no matter what lens > is mounted (or even, if I remember it right, when no lens is fitted). My SP 90/2.5 reports as 2.5, not 2.8 (or were we talking zooms)? With no lens fitted, no aperuture value is reported (though I can change the shutter speed by manipulating the above-mentioned links). > This doesn't matter most of the time - after all, every auto-exposure > camera Pentax built prior to the introduction of the KA mount managed > to perform perfectly well without knowing the maximum aperture of the > lens. All you need to know is that when stopped down the lens will > need so many more stops of exposure than the wide-open meter reading. > I'm also a little dubious as to whether the Adaptall lenses were an > exact match to the Pentax A lenses when it came to partial stop-down > (i.e. controlling the aperture from the body, with the lens in the > "A" position). I could have been worrying unnecessarily, but when > I was really concerned about precise exposure I always used Av mode > (especially if using the TC, which added another mechanical link). Well, it behaves exactly like an A lens: aperture info in the VF at 'a', and not at the other settings. FA's are better: they return the aperture-ring setting to the viewfinder. Tested with an A50/1.4 and FA 28-70/4 on a Z-1p... -- Regards, Lucas -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
