Focus Locus Offline Upload & Sell: Off
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p.1 #8 · p.1 #8 · Canon 1 DX Setting (Lens drive when AF impossible) | |
OntheRez wrote:
The note refers to "super telephotos." Any idea when they get super? I'm guessing this isn't really applicable to say the 70-200 f/2.8. Anyone with a thought on this?
The mass of the moving elements, and the degree of rotation between MFD and infinity, are why I think the superteles benefit from the switch, whereas other lighter element group lenses with less helical movement do not. It takes more time to move heavy elements, and longer distances of rotation add to the time lost finding focus again. The switch prevents the camera getting completely lost, when you know where the subject is, and can touch focus again to get it back without the lens having to grind through 100 degrees of helix to get back to where you left it.
I just opened my bag to check before posting this, so these are my own ball park "clock" estimates of "crank angle" between MFD and infinity that I found on my equipment, not official specs from Canon:
- 70-200/2.8 II is 110 degrees
- 200/1.8 is 180 degrees
- 300/2.8 is 240 degrees
- 400/2.8 is 270 degrees
Unlike the other lenses, the 200/1.8 needs power from a camera in order to check, and it is best to set the focus switch to manual if the battery is weak. Ask me how I know!
I don't own a 5, 6, or 8 so I can't give you any idea how much twist of the wrist it takes to crank those elements around through their focus range, but I imagine those longer teles would also fall somewhere between 200 to 300 degrees.
Math has never been my strong suit, but I think element diameter plays a role here somewhere, in terms of the energy and time it takes to crank the elements back and forth inside the tube.
I think Canon considers "SuperTelephoto" primes to be the white 2, 3, 4, 5, 6, 8, & 12. At least that is how they have been arranged on their rebate forms and sales literature over the years. Except the 12 of course. That was special order.
Contrast this to some of the smaller, shorter black primes, with as little as 40 degrees of rotation lock to lock.
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