Perhaps the same way as the Nikon's do with an AF lens and the aperture not at minimum? Relative aperture based on the aperture simulator and a little math from the max aperture info given by the lens to the camera. I'm seriously doubting that there is an electronic encoder added to the aperture ring, unless someone who has disassembled one feels like telling me differently. Electronic communication of exact max aperture at the current zoom length would be required to make the display work correctly with variable-aperture zooms, which is likely why it doesn't work with A lenses which lack datalink capability.
Note that even if there is an aperture encoder in the lens, your idea may not work for mechanical reasons. taking the lens off of A will mechanically limit the minimum aperture the lens can be set to. While I can see a way around it (If you're taking the setting from the lens you won't want to drop the aperture any smaller in the first place) I can also see this being an issue, especially with variable aperture zooms (Do you take the absolute aperture set and give up minimum aperture at all but the widest focal length? does the ring only give relative aperture like it would on an older body?) -Adam P. J. Alling wrote: > Read the specification. It's available on Boz's K mount page, > (http://www.bdimitrov.de/kmp/). The only cameras that use the F ring > use it's mechanical properties, but it reports the set f-stop > electronically to the camera body for display purposes. Try an F/FA > lens off the A position on say a MZ/ZX-5n then try an A lens the same > way. The do a thought experiment after reading the K mount evolution > page on Boz's site, ask yourself how the camera knows to display the > aperture for the F/FA in the viewfinder. > > Adam Maas wrote: > > >>No, the aperture ring on F and FA lenses is mechanical, not electronic >>as on the PanaLeica 4/3rds lens(es). >> >>-Adam >> >> >>P. J. Alling wrote: >> >> >> >>>The F and Fa lenses already report that set aperture to the camera body, >>>if it wishes to read it. They could be used entirely electronically as >>>is the new Panasonic/Leica 4/3 duo. No real complication at all, the >>>extra control costs pennies to implement, and Pentax keeps is promise >>>about keeping aperture rings on DFA lenses while still screwing film >>>body users. Everybody wins! >>> >>>John Francis wrote: >>> >>> >>> >>> >>> >>>>On Sat, Sep 02, 2006 at 10:19:57AM -0400, K.Takeshita wrote: >>>> >>>> >>>> >>>> >>>> >>>> >>>>>Adam Maas mykroft at mykroft.com Sat Sep 2 08:49:28 EST 2006 >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>>>>400/4 with SSM would be neat. Can't see any good reason to make it >>>>>>>DFA, though. DA will make it smaller, cheaper and just as good. >>>>>>> >>>>>>> >>>>>>>Jostein >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>> >>>>>>Actually, the size constraints on a 400 are all in the glass diameter >>>>>>(for a given aperture), format is essentially irrelevant to this, at >>>>>>least until you start talking LF, so there's zero reason to make it a DA >>>>>>lens since it will be the same size anyways. >>>>>> >>>>>> >>>>>> >>>>>> >>>>> >>>>>Exactly. After certain size (say 200mm or so), there is no reason to make >>>>>it a DA. >>>>>Still some hope for FF wishers :-). >>>>> >>>>> >>>>> >>>>> >>>> >>>>I thought a significant difference between DA and DFA was the presence >>>>of an aperture ring. Sure, longer focal lengths are going to have an >>>>image circle larger than an APS-sized sensor. But that in itself isn't >>>>enough to make it a DFA lens. >>>> >>>>If, as we expect, these new lenses incorporate a new auto-focus mechanism >>>>then they are designed for use mainly on new cameras. As such, I doubt >>>>that Pentax would bother with the extra complication of an aperture ring. >>>> >>>> >>>> >>>> >>>> >>>> >>> >>> >>> >> >> >> >> > > > -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
