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70-200/4 IS USM PLUS 2X TC?

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Matthijs Claessen , Jun 27, 2011; 06:45 a.m.

Note that with some brands the aperture change by the extender is not communicated. The AF will be operational.

This can also be done with Canon by taping off some of the contacts. (Canon advises against that but it works, or so I am told.)

The results with the x2 III extender aren't that bad by the way. (With the II they're less good. See the mouse over.)

Kind regards, Matthijs.

Robert Thommes , Jun 27, 2011; 08:01 a.m.

Matthijs,
Thanks for comparing the two TCs. You're right, the 2X III is really not that bad at all. Now becomes a question of expense and loss of wider aperture....and loss of AF(?).

Marc Bergman , Jun 27, 2011; 09:46 a.m.

Robert,

Have you thought about renting a lens for your trip? LensRentals has a great selection for your Canon.

http://www.lensrentals.com/for-canon

Robert Thommes , Jun 27, 2011; 10:10 a.m.

Yes, I have considered renting. But this might give me a good excuse to just go out and purchase one, too. I'm sure that a 100-400mm would get lots of use for my frequent nature shots.
But.....I could not make such a buy without the sale of my tried and true 70-200/4 IS. Therein lies the dilemma.

Philip Wilson , Jun 27, 2011; 10:50 a.m.

What are you planning on shooting with such a long focal length? If you are thinking birds etc... you may find that the AF is too slow with a TC (they slow down the AF). If you really need 100-400 on a regular basis then trade your 70-200. But if you will mainly shoot in the 70-200 range then you may want to rent or consider a prime (which are cheaper than zooms) such as the 300 F4 and 400 f5.6

G Dan Mitchell , Jun 27, 2011; 10:51 a.m.

"... your lens is actually a 448mm fl with your current 1.4x converter."

A way to avoid the blow-back about the focal length not changing (which is, by the way, absolutely correct) is to phrase this important point more or less as in the following:

"... the angle of view provided by your lens is actually equivalent to that of a 448mm fl on full frame with your current 1.4x converter."

Dan

Steve Dunn , Jun 27, 2011; 02:17 p.m.

Note that with some brands the aperture change by the extender is not communicated. The AF will be operational.

If by "operational" you mean "will try to work but may be completely useless." The f/5.6 limit is there for a reason; here's a simplified explanation.

Phase-detection autofocus essentially samples light from opposite sides of the beam of light being projected into the camera by the lens. If the subject is in focus, the two sensors will see the same thing; if the subject is out of focus, the images seen by the two AF sensors will be shifted relative to each other, with the direction of the shift depending on whether the subject is closer or farther than the focused distance and the magnitude of the shift depending on how far out of focus the subject is (all else being equal).

As the lens gets slower, this beam gets narrower, and at some point the beam becomes narrow enough that the AF sensors lie outside the beam of light. At this point, obviously, AF no longer works. In general, the farther apart the two samples are, the better the AF system works, but the tradeoff is that this would require a faster lens (and if you've ever wondered why the high-precision AF sensors in some bodies require faster lenses, now you know). f/5.6 is a reasonable compromise between the two. f/5.6 is not a hard-and-fast cutoff; there's a margin of safety in there, which is why a third-party zoom lens that's f/6.3 on its wide end can still autofocus even though it's slower than the supposed requirement of the camera (and such lenses lie to the camera, stating that their aperture is actually f/5.6, to avoid having the AF system shut itself off). But f/8 is a whole stop slower than the camera's designed to use, and you shouldn't count on it working at all; even if it does, don't expect it to be as reliable as with a lens that's f/5.6 or faster.

FWIW, I once tried using the Canon 1.4x II TC on the 28-135/3-5.5.6 IS USM. (This is not a supported configuration, and can only be used if you're careful to keep the zoom toward the long end of its range; if you zoom back to the wide end, the rear element of the lens will strike the front element of the TC, potentially damaging both.) Since the zoom is f/5.6 at its long end, it becomes f/8 with the TC. The body doesn't know this, because the lens isn't designed for use with a TC and therefore lacks the extra contacts necessary to detect the TC's presence, so the body tries to AF. I don't recall whether I did this with my Elan 7E or 20D, but the end result was that even in good light with a high-contrast target, the AF system simply hunted between near and infinity and was unable to find anything to lock onto.

Robert Thommes , Jun 27, 2011; 04:19 p.m.

Philip Wilson,

To answer your question, I'm planning on shooting wildlife in National Parks. Birds being the least of my interests. I'm thinking more like larger mammals such as deer, moose, bears, elk, etc. This entire venture is new to me.
If I felt my 70-200 with 1.4X TC could handle most of my needs, I'd stop there; as I have this.
I know that the results of such a combo are good. But is the length(reach0 sufficient? I'm not so sure on that.

Mike Hitchen , Jun 27, 2011; 07:29 p.m.

Large moose are about 6 feet at the shoulder and black bears are 3 to 4 feet. So you could take pictures of people at different distances and see how far away you are before cropping becomes unfeasible. We were taking photos of grizzlies from anything up to 100 feet away with a 300mm lens with decent results.

Robert Thommes , Jun 27, 2011; 07:49 p.m.

Mike,
30 yds is pretty close for grizzlies. Were you on foot, or in a car? What park? What season?
Thanks


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