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.
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
>>
>
>
>
>
--
Things should be made as simple as possible -- but no simpler.
--Albert Einstein
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