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Old May 31, 2005, 5:18 PM   #11
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I think you mean that I am physically moving forward or back after setting focus. This is certainly a possibility, but I'm using a monopod, and don't think that I would do so in 20 or 30 shots without being aware of it. I've tried to make it clear that I don't think the extender is defective. The problem only occurs with the extender, however, so I do think it has something to do with the way I am using the extender, or how the extender is affecting the camera's autofocus function. It is as though the focal plain is 8-10 feet beyond where it should be.

I was just hoping that someone might have seen this happen and know what the cause might be.
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Old May 31, 2005, 7:48 PM   #12
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Im going to have to disagree with Lboy, the 2x converter makes autofocusing dangerously slow, and not to mention inaccurate. Using manual focus will get you a much better shot most of the time.

Having said this, it will produce good pictures if you get used to it.

I got my 2x converter for $140AU ($100US) brand new so i really shouldnt be complaining at all.
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Old Jun 1, 2005, 1:57 AM   #13
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twofruitz wrote:
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Im going to have to disagree with Lboy, the 2x converter makes autofocusing dangerously slow, and not to mention inaccurate. Using manual focus will get you a much better shot most of the time.
AF will be less, yes. Your wide-open is now F5.6 thus 4x less light for the camera to work with to focus. Also, the high-accuracy center focus point is no longer enabled. That only works at F2.8 (or lower).

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Old Jun 1, 2005, 5:48 AM   #14
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Quote:
Im going to have to disagree with Lboy, the 2x converter makes autofocusing dangerously slow, and not to mention inaccurate. Using manual focus will get you a much better shot most of the time.
well bad luckyou. I'm just not experiencing this slow auto focus at all. maybe indoors, but I dont use this combination for that. I have been getting very sharp clean results on fast moving subjects. centre point focus, ai servo. 200mm with 2x extender.
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Old Jun 1, 2005, 9:09 AM   #15
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Lboy, what kind of camera are you using? I'm using the first generation Digital Rebel. Could it be that its autofocus isn't up to the task, or requires a little more skill than I possess? I'm always looking for an excuse to buy new equipment; would a 20D perform better under these circumstances?

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Old Jun 1, 2005, 9:56 AM   #16
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Like barthold have noted, the 20D only works more precisely with f/2.8 lenses or larger -> at f/5.6 with the teleconverter the high-resolution AF sensor is not enabled...

Also it's not just less light, but the amount of de-focus data are just not there for the camera to work with. Try it, even in -2EV darker environment the f/2.8 lens still focus better than slower lenses, regardless if the ambient light is even +2EV brighter with f/5.6: http://konicaminolta.com/products/co...x7/ope01b.html
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Old Jun 2, 2005, 3:53 AM   #17
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tmilner,

EOS-1D Mark II, for the most part. But also often use a 20D and its also fine.

Really, you shouldn't be having a problem with defocus at f5.6 in terms of actually achieving auto-focus. No one is arguing that it wont be somewhat slower. After time you learn to instinctively select an appropriate point of contrast when possible (almost always). There's more tophotography and camera handling than point, shoot, learning charts figures and camera maths.

Your back focus problem is something else.

Anyway once more. Killdeer, don't worry about this combination.
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