Another bad K-3, what is with this.

Started 9 months ago | Discussions thread
Gerry Winterbourne
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Re: Another bad K-3, what is with this.
In reply to sfa1966, 9 months ago

sfa1966 wrote:

Roland Karlsson wrote:

Nuffin wrote:

My K3 is in service for backfocus issues. Kinda disappointed mine had this issue. I'm keen to see if the service department will blame it on the lens, the body, or me.

I spoke to a tech recently and he somewhat indicated that I wasn't testing my focus properly. We'll hello! If I focus on something (like batteries lined up at 45 degree angle) and get a focus indicator on the middle, if I take a shot (even with a tripod and on timer) why is it back focusing?

Please understand though that the focus area is much larger than the red focus indicator. So, check that it is not actually locking focus at the battery beside it.

Even with the new 25-point array of AF points in the centre area of the viewfinder? I thought that one of the advantages of the new AF design was to avoid this "much larger area" problem.

PDAF needs a baseline width from which to assess range. Think of the rangefinders on WW1 battleships - very wide base to give accurate range over long distances. The PDAF baseline is the distance between the two microlenses http://graphics.stanford.edu/courses/cs178-10/applets/autofocusPD.html

Narrowing the baseline would reduce AF accuracy so if the new system does use smaller AF points perhaps that's why there are problems.  It seems more likely, though, that the greater number of points is to help focus tracking.

On models up to the K-3 the centre point (and most of the others) are crosses: two pairs of lenses at right angles to each other.  The two baselines are roughly the diameter of the centre circle visible in the VF.  Even if the K-3 is a bit smaller I think the circle would still be a good guide.

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Gerry
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First camera 1953, first Pentax 1985, first DSLR 2006
http://www.pbase.com/gerrywinterbourne
gerry.winterbourne@ntlworld.com

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