[MSM]

All the cross type sensors are in that large vf scribed box = 9.

Ignore the center sensor within that large vf scribed box and just consider the 8 cross sensors around the perimeter of the box for the sake of this discussion.

On my K5,
a. When i move an object of high contrast into the large box from the left box side, the left side sensors don't activate until the red vf indicator is on that high contrast area. Same with the top, bottom and right sides of the large box except that each time the object has to move into the scribed vf box from the outside areas.

b. When i have an object of high contrast already inside the large box and move it toward the 3 left box side sensors, they activate way before the object reaches them. Same with the top, bottom and right side sensors of the 9 sensor box.

c. Another way of saying this is that the left box side sensors are accurate to the red indicator when approached by an object from their left side. When the left box side sensors are approached by an object from their right side, they activate way before the red indicator dot is reached.

Note: this knowledge might help in some situations, but primarily i use the center sensor.

On a different subject, I don't get why Pentax continues to use such large sensors, unless it costs more for smaller sensors. Do large diameter sensors collect more light?? If so, one would expect Pentax AF to be more sensitive in low light.

Interesting Phil. I think this is what I was seeing with my K5. I use the center AF the most. I find if I place the contrast object at the top or right side of the 'center box' it seems to give me a better AF on the desired target.

[jmg257]

Here's what I came up with....
The sensor arrays are indicated by the green & blue lines.



-The vertical legs seem to overlap the adjacent sensors' vertical leg.

-2 AF points will always light up in Auto Select 11 when 1 of the corner AF sensors finds lock...the AF point for the sensor finding lock and the adjacent AF point in the direction (vert or horiz) of the array doing the locking. For example, if the vertical array of the Upper Right AF sensor area finds lock, the Center Right AF point will light as well. If the horizontal array of the Upper Right AF sensor finds lock, the Upper Center AF point will light.

2 AF points MAY light up in Auto 5...if the adjacent sensor in the direction of the array finding lock is active. For example, if the vertical array of the Upper Center AF area finds lock, the Center AF will light too. If the horiz array of the Upper Center finds lock, it will be the only one to light (since upper left and upper right are inactive).

[simico]

On a different subject, I don't get why Pentax continues to use such large sensors

My guess: it's cheaper to continue using existing hardware (and do some minor tweeks for newer generation cameras) than develop and manufacture a totally new hardware which also requires new production line / tools.

My only wish for a K-5 successor is smaller and more AF sensors (besides fixing existing bugs, of course). But I guess Pentax doesn't really want to invest in new production line for totally new AF hardware.

[rawr]

I guess Pentax doesn't really want to invest in new production line for totally new AF hardware.

The K-30's new AF module looks new to me. New lenses, new sensor, new assembly etc. An even fancier one for the K-5's successor probably wouldn't cause them too much difficulty.

[jmg257]

There are a few Hoya patents for "Automatic Focusing Apparatus".

One shows a 3x3 continious grid ('09 #7496290), as I showed in post #68 in this thread. For a while I thought this was the base of the current AF system...now I see a few patents for a 3x7 array ('05 #6937818, '09 7493034), one which shows it can be configured exactly as the typical 1+3x3+1 focus area in one of the drawings/figures, so this might actually be the 'current' AF as it has evolved, along with the + color sensor improvments as described in other patents.

There are also a couple 2011 patents (2011/0122280A1) for a 5x9 array which could be the next AF sensor...has all kinds of improvements...looks pretty cool!