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p.2 #16 · Probably crazy... 300 2.8 questions | |
rwalkernm wrote:
Chris,
The 100-400 is not a fast focuser (nor is my copy particularly accurate unless there is plenty of light). The 300 + 2x TC is easily faster. The 300mm seems faster to me than the 135 F2 lens, and it is very accurate.
I know I saw some specs somewhere about how much the focusing speed is reduced with the 1.4x and 2.0x TC's, but it still Feels "fast" to me. Wikipedia says with the 1.4x attached, AF speed is cut in half, and with the 2.0x it's cut to a fourth of normal. I just can't remember where it was I saw actual timings in msec.
How the 300mm + TC compares to the 400mm + TC probably just scales with the basic AF speed of the native lens.
If I stack the TC's, (2.0x on the 300mm, then 1.4x on the camera), it will still try to focus on the 1DMkIII, but tends to oscillate focus on it's way to finding where it wants to be. If I start off too far from being in focus, it will not even try to focus.
Maybe someone else has better specs -- these are mostly the "feel" of the lenses.
Bob
I've seen Canon specs on it, just that can not remember where. Either way, 1.4xTC supposedly cuts the AF drive speed to 2/3 and 2xTC reduces the lens AF drive speed to 1/2 of its native value.
However, Canon likes to express the AF drive speed in terms of AF group travel time which makes more practical sense.
Therefore, when it comes to 300 f/2.8 IS, I believe its AF drive speed is 0.4 sec (probably a bit better too.) Therefore, with the 1.4xTC the combo, the speed would be 0.6 sec which starts to get a bit sluggish and it is in the range of 500 f/4.5L and 200 f/1.8. Add 2xTC to the lens, and now we have 0.8 sec AF drive speed which is not very good for fast action at all.
Just for another reference point, Canon quotes the AF drive speed for 85L MkII as 1 sec.
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