John Francis
Tue, 31 May 2005 10:30:37 -0700
>On Tue, May 31, 2005 at 12:45:33PM -0400, Collin Brendemuehl wrote:
>>
>> Because the two lens types step down with different mechanical
>> ratios between the arm and the aperture blades, the camera
>> (in its current iteration) does not know how to move or release
>> the arm.
>>
>> But this could be fixed in software, by having the camera be
>> smart enough to detect non-A lenses (all pins shorted, and
>> no "A") controlling the stepper position would be accomplished
>> in an alternate fashion.
>
>You're making a very big assumption here - that the response
>to any given actuating arm movement is the same on any two old
>pre-A lenses. There is no requirement for this to be true
>(the actual response is controlled by the lens aperture ring).
>
>You'd probably not be off by more than a stop or so in most
>cases, but there again that's true even if you use the same
>movement as you would use for "A" lenses. The worst case is
>when you are trying to use small apertures - any small error
>in sensing the lever position leads to large exposure errors.
>
>
>Ask yourself this question: Why did Pentax change lens design?
>They already knew how to create non-linear mechanisms; there's
>one in (almost) every single "A"-or-later lens. But instead
>of keeping their existing lens mechanism, and producing a body
>with an actuator mechanism capable of controlling such a lens
>in the way you propose, they changed to a design that allowed
>much better control at small apertures, and made sure that
>all lenses built to that design had a calibrated response.
>
The camera would have to make no assumptions at all.
A simple calibration stepper movement could inform the firmware
what the minimum, maximum, and in-between values are.
Dynamic calibration. Again, it can all be done through
software control of the stepper. This could easily end up
being more accurate than the detents allow.
I'm drafting a letter to Pentax' marketing/engineering department
and proposing not only this but also some open software
characteristics as well as the formation of a developers
group, allowing custom software integration into the cameras.
The industry is ready to mature to this point. The important
question here is, is Pentax ready?
Collin
Sincerely,
Collin
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