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cross-type AF point on 10D ?

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Thread started 21 Mar 2007 (Wednesday) 04:35   
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mxp
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does the eos 10D have a cross-type AF point ?
:rolleyes:

Post #1, Mar 21, 2007 04:35:34




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John_B
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mxp,
Yes on the center AF point only

Post #2, Mar 21, 2007 06:08:01


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Doug ­ Pardee
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As John said, yes the center AF point is cross-type. However, it doesn't have the triple-precision f/2.8 sensor that the 9-point AF on the 20D/30D/XTi/400D has.

Post #3, Mar 21, 2007 10:28:13




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bauerman
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Can someone go into more detail regarding this topic - its interesting to me and I would like to learn more. What exactly is a cross-type AF point vs. the other AF points in the 10D or any other camera for that matter?

Post #4, Mar 22, 2007 12:45:47




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Doug ­ Pardee
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bauerman wrote in post #2913136external link
Can someone go into more detail regarding this topic - its interesting to me and I would like to learn more. What exactly is a cross-type AF point vs. the other AF points in the 10D or any other camera for that matter?

Most AF sensors are only sensitive to edges that go in one general direction: either horizontal edges or vertical edges, but not both. A cross-type sensor is sensitive to both horizontal edges and vertical edges.

Post #5, Mar 22, 2007 13:01:23




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bauerman
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But this functionality is only available within the confines of certain apertures? Does that change depending on the lens that you have attached to the body?

(Thanks that explanation by the way - makes a lot of sense and is not something I was familiar with before now.)

Post #6, Mar 22, 2007 13:06:11




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Doug ­ Pardee
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bauerman wrote in post #2913216external link
But this functionality is only available within the confines of certain apertures? Does that change depending on the lens that you have attached to the body?

The autofocus system on the 10D, as on all of the Canon DSLRs except the 1-series, is designed for lenses of f/5.6 or faster. Yes, it depends on the lens (and often on the current focal length setting), because autofocus is done with the aperture wide open. What counts is how wide the lens aperture can go (at the current focal length setting).

There are some third-party zoom lenses that are f/6.3 at the long end, but lie to the camera and claim that they're f/5.6 so that the camera will autofocus.

The 9-point AF system used on the 20D, 30D, and XTi/400D also has a triple-precision non-cross sensor—sensitive to vertical edges only—at the center AF point that is turned on when a lens of f/2.8 or faster is fitted. So with an f/2.8 lens, the center AF point is still cross-type and therefore still sensitive to both horizontal and vertical edges, but it gives more precise results with vertical edges. This triple-precision sensor is not present on the 10D or any of the other Canon DSLRs with the 7-point AF system.

Post #7, Mar 22, 2007 15:02:49




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bauerman
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Excellent information Doug - and much appreciated. It makes a lot of sense and I especially liked the bit about the "lying lenses" that fibbed that they were f5.6 so the camera would autofocus. :-)

Are there any links or websites that you know of that explain this subject in more detail that you could point me to? Thanks.

Post #8, Mar 22, 2007 15:08:51




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adas
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bauerman wrote in post #2913848external link
I especially liked the bit about the "lying lenses" that fibbed that they were f5.6 so the camera would autofocus. :-)

I would stay away from those lenses. If they're lying they were f/5.6, they most likely "pretending" they achieve consistent focus. It's not Canon who's set a limit at f/5.6 for AF. It's the geometry of the AF sensor that won't allow a smaller aperture.
I don't have links, but you can google for PHASE DETECTION AUTOFOCUS.

Post #9, Mar 22, 2007 17:45:22


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bauerman
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Thanks adas - I will do that.

Post #10, Mar 22, 2007 18:13:44




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Hellashot
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adas wrote in post #2914663external link
I would stay away from those lenses. If they're lying they were f/5.6, they most likely "pretending" they achieve consistent focus. It's not Canon who's set a limit at f/5.6 for AF. It's the geometry of the AF sensor that won't allow a smaller aperture.
I don't have links, but you can google for PHASE DETECTION AUTOFOCUS.

Then you are telling people to stay away from the Bigma. :) I have it and it sure does get AF right. :)

Post #11, Mar 22, 2007 21:04:07


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