I don't think I'm missing the point, the point is the lens motor is powered neither at 11.1 V nor at 7.2 V. It is powered at a voltage which I don't know, but which is undoubtedly the same whichever body you are using whith whatever battery voltage/number of batteries you are using. The lens is NOT powered directly from the battery, but from a circuit which delivers constant voltage whichever body/battery combo you are using.Mt Spokane Photography said:You missed the point, battery capacity has little effect, its the current driving the lens motor, and that is based on the voltage and resistance using ohm's law E=IR.pierlux said:Canon Rumors said:*UPDATE 2*
The battery does help a camera body autofocus an EF lens faster.
From Chuck Westfall… “In addition, the EOS-1D X achieves a higher lens motor drive speed with select L-series USM telephoto lenses than the 5D Mark III because of the 1D X’s more powerful battery pack.”
Exactly, power, i.e. V x A = W.
1 x LP-E4N is 11.1 V x 2450 mAh = 27.195 W
2 x LP-E6 is 7.2 V x 1600 mAh x 2 = 23.040 W
27 W vs. 23 W, not much of a difference, but it's there.
Given the same internal resistance of the lens motor, the current would be about 11.1/7.2 times larger or 1.52 times as much current going thru the motor. Presumably the internal resistance of the bigger battery is lower, so it would have little effect.
That will drive the motor much faster.
Sure, the internal resistance of a big battery is lower than that of a smaller one, but resistance comes to play only when you exceed a certain current absorption from the battery so that the battery itself is no longer able to supply the nominal voltage. When you read the battery specs, say, 7.2 V - 1600 mAh, the internal resistance of the battery has already been taken into account, you don't have to worry about that. And when the battery performace declines, it is exactly the battery's internal resistance which increases, giving you a lower voltage even at a low current absorption.
When you're using your camera, you're draining power from the battery which is generally lower than the max power the battery is capable of delivering, otherwise I would claim bad engineering. That's why we are discussing about the possibility for the 7DII to drive simultaneously a big lens AF and IS plus a 12+ fps burst either with a big batt or two smaller ones. But, again, it's a matter of power (W), not simply voltage alone, or current alone. Should only voltage matter, nothing would prevent a camera maker to equip their products with 24 V or 36 V power supplies...
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