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04-15-2008, 03:46 PM   #1
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Join Date: Oct 2007
Location: Wisconsin
Posts: 273
Program mode with non-A type lenses

This should be feasible. Let me explain.

When Pentax went from M to A, the biggest difference was the method of aperture actuation. M-type and earlier cameras used an actuation method that was proportional to the diameter of the aperture opening. This didn't really matter at all to the camera, because it would always simply smash the coupling as far as it would go. However, with the advent of the KA-mount, the mount went to a system that was proportional to the area of the aperture. This was because with A-type lenses, the camera varied the amount it moved the aperture actuator, and the linear proportion, with area, was the only possible means, as the lenses didn't transmit FL data yet, and even if it did, calculating aperture data for AE would be very processor-intensive. Any A-type lens set to f2.8 would be the same as far as the camera knew. However, an M-type 85mm f2 is different from an M-type 50mm f2. My solution is this. With manual focus lenses on startup, you're required to enter FL anyway for SR uses. SO, what if there were an extra option, saying that this was an M- or K-type lens, and this is its maximum and minimum aperture? Because the camera would know everything about the lens, and has sufficient processing power, you'd be able to have full autoexposure, as long as you set the lens to its minimum aperture on the aperture ring. What do y'all think?

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