Canon Auto Focus layman report

Just trying to read through all the marketing for Canon's AF. Please feel free to correct and add understanding. Let us only discuss one thing. Center Point AF in One-Shot mode NOT tracking. Thank you.

To summarize the 20D report:
* "newly developed"
* Center focus point is vertical-line sensitive at f/2.8 and horizontal line sensitive at f/5.6.
* Base length of the center AF point is twice as long as f/5.6 compatible sensors.

5D report:
* Center focus point is vertical-line sensitive at f/2.8 and horizontal line sensitive at f/5.6.
* Base length twice as long as previous models. A total of three vertical-line center points are active at f/2.8. Two of these are "invisible". Another "invisible" two work for f/5.6 horizontal lines.

To summarize the 30D report:
* Same as 20D.

To summarize the XTi report:
* Same as 30D

To summarize the Mark III report:
* "New very precise AF"
* Center focus point is vertical-line sensitive at f/2.8 and horizontal line sensitive at f/5.6.
* Read report for tracking if interested

Canon's best auto focus up till the 40D is described as "high-precision cross-type" Which means "vertical-line sensitive at f/2.8 and horizontal line sensitive at f/5.6". With an f2.8 lens both vertical and horizontal axis are working. The only difference on paper seems to be that the PRO bodies do tracking much better. People complaining about the 30D auto focusing are tracking something or not using an f2.8 lens. The XT (350D) does NOT have a "High Precision" center point AF. On paper the 5D (not taking the 40D into account) has the best center single point AF ability.

20D
http://www.canon.com/c​amera-museum/tech/report/200​409/report.html

5D
http://www.canon.com/c​amera-museum/tech/report/200​509/200509.html

30D
http://www.canon.com/c​amera-museum/tech/report/200​603/report.html

XTi
http://www.canon.com/c​amera-museum/tech/report/200​609/200609.html

1D Mark III
http://www.canon.com/c​amera-museum/tech/report/200​703/200703.html

If I understand you correctly, I think you're confusing the 5D's invisible AF points with the center AF point. The invisible ones are within the center circle, but not at the actual center AF point--they are separate AF points surrounding the center point.

Yohan Pamudji wrote in post #3874827
If I understand you correctly, I think you're confusing the 5D's invisible AF points with the center AF point. The invisible ones are within the center circle, but not at the actual center AF point--they are separate AF points surrounding the center point.

Oh yes I know this, but they "assist" the center one...

From the 40D White Paper:

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A newly-developed AF sensor with 9 cross- type AF points greatly boosts AF performance, improving both AF detection precision and extreme-defocus subject detection capability.

AF sensitivity is now EV -0.5 to EV 18. All AF points work as cross-type points at f/5.6 or better. Both vertical- and horizontal-line sensitive focus detection thus works with any AF point for stable focusing.

High-precision AF is attained with fewer AF failures with hard-to-focus subjects. Also, with the sensor pitch reduced from 16µm to 14.4µm, detection performance is more accurate.

The center AF point has a cross-type AF sensor sensitive to vertical and horizontal lines at f/2.8. This is a first in an EOS camera. Previously, the central sensor for f/2.8 or better was only vertical-line sensitive. Because the f/2.8 sensor is a diagonal, cross-type sensor, it does not obstruct the f/5.6 sensor positioned vertically at the center.

The upper center, center, and bottom 3 horizontal-line sensitive sensors are in a 2-line, zigzag configuration. With this double focusing system, inconsistent focusing detection is reduced.

By using the 2-line focusing sensors described above, a subject in extreme defocus can be detected and AF control is quick and easy.

To attain more stable AF performance than before, the AF unit has more precise AF optics and environmentresistant construction and materials.
---------

Sounds pretty good!

So if you don't have an f2.8 lens you don't get full functionality of AF?

tmcman wrote in post #3884772
So if you don't have an f2.8 lens you don't get full functionality of AF?

Without an f2.8 or faster lens, you don't get the benefits of the high-precision focusing mode, however, you should theoretically still see some benefits from the other 40D AF improvements.