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How often do you use AF in selective (SEL) mode?

The reason why I'm asking is that I've noticed that on a Pentax body (K10D and K-5) the AF is a lot more accurate when in AUTO mode than in SEL mode. The images focused in AUTO mode are razor sharp (especially on K-5) and the same shots in SEL mode tend to be a bit blurry.

I've also noticed that in AUTO mode often two AF points are often used together (the red dots in viewfinder). This never happens in SEL mode. Can you please help me understand this?

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I have never used a Pentax but by "SEL mode" do you mean the mode where you can select the auto focus point? And for AF mode, does it always happen that two points are used or it also happens that one or three or more points are used? –  baoye Dec 9 '11 at 16:02
    
The poster also asked this same question here it looks like: pentaxforums.com/forums/pentax-k-5-forum/… –  dpollitt Dec 9 '11 at 22:33

2 Answers 2

SEL or Select mode is a Pentax focus mode that allows you to select which point to focus on out of the available focus points. Auto mode is on the other hand going to select from the available focus points(11 in the case of the K10D) whichever it feels is the best using the TTL phase-matching system(SAFOX VIII) and the subject. A third option is available named center, and all it does is select the center AF point.

As far as I know, the Pentax K10D does not use any type of area AF system. With that said, if you did see multiple focus points light up, it is probably just telling you that they are both in focus currently. SEL mode is only really activating one focus point at a time, so it is assumed the rest are turned off and will not light up at all under that mode.

If performance is truly different as in "missed shots" while not moving the camera or subject, but just by flipping the focus mode, then you have a issue that should be looked at by a Pentax repair center.

To resolve your issue, simply select AUTO when you want all points to be active, and SEL when you want to select a single point outside of the center(use center for that).

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I think Pentax Forums user philbaum has it in the post @dpollit linked to. When you're using auto mode, a focus point which is nicely aligned with something high-contrast is selected. When you're using a specific focus point, that might not be the case, since as with all autofocus SLRs, the focus sensors are a) surprisingly larger than the red indicator dots in the viewfinder and b) not necessarily precisely aligned with those dots. So it's likely you and the camera have different ideas about what the AF target is.

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