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11-19-2010, 04:59 AM   #1
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Pentax K-x real focusing points and their alignment

Hi Folks,

Recently I got Pentax K-x. After reading some forums (including this one, but without registration) and some experiments with my new camera, I have found that the real focusing points are a lot bigger that the imaginary focusing point marks so often pictured on the K-x viewfinder images (the standard K-x viewfinder actually does not have these marks, but still their location is often indicated in the pictures).

What I mean by saying a lot bigger? Based on a few simple experiments (by repeatedly focusing on the mark on the uniform non-contrasty surface, and then pointing the camera slightly above, below, to the left, to the right from the mark) I made a conclusion that the central AF point fully fills the space between the round bracket marks in the viewfinder. The other cross type AF points are not much smaller (if smaller at all) than the central one.

Are all K-x cameras like this, or I got atypical (faulty?) one?
I guess that all of them should be like this.

The other thing is that in my instance all 11 AF points seem to be shifted a bit to the right (in relation to the viewfinder markings and AF points approximate locations pictured for Pentax k-x). It looks like focusing screen misalignment issue.
Should I be concerned about this and request servicing (Camera is brand new I got it just a couple of weeks ago), or is this ok?
Is it an indicator of some deeper problems, or simple focusing screen misalignment? Can it be fixed easily?

Thanks,
elg

11-19-2010, 05:56 AM   #2
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Aaaarrrrgggghhhh!!!!

Where did you ever get the idea that the focus points in the K-x (or any other DSLR) were ever anything other than a region? Of course they are bigger than microscopic dots on any focus screen.

JFC.
11-19-2010, 06:07 AM   #3
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The focusing points one can see in the viewfinder (although they aren't luminous in K-x) correspond to regions of the sensor. But I'm not sure what you mean by "focusing points"... The dots marked on the viewfinder of your camera?

If your viewfinder looks weird and bothers you while shooting, you should return the camera or send it to Pentax to fix it.
11-19-2010, 06:16 AM   #4
elg
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QuoteOriginally posted by rawr Quote

Where did you ever get the idea that the focus points in the K-x (or any other DSLR) were ever anything other than a region?
Of course they are not dots, but I did not expected them to be that big! I think that the 9 point array in the middle covers or nearly covers the whole central area fully (i.e. without any gaps in between). I'm not saying that this particular thing is a problem.

Now the other thing (focus point shift) might be a problem (this is why I'm asking for advice).

Btw. On my Nikon D70s the AF points (the real ones) more or less fit within the AF point markings on the viewfinder (although they are slightly shifted to the left, the shift is much smaller than the one on K-x, and they are pretty much inside the markings).

So the question is should the K-x be considered faulty (as it may be symptom of something worse) because of this (as a central point is not entirely in the center of the viewfinder, but noticeably shifted a bit to the right).
This misalignment on k-x is roughly 2-3 times bigger than on D70s, and while on D70s it seems acceptable, on K-x - not so acceptable.

Cheers,
elg (Erika)

11-19-2010, 06:20 AM   #5
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I'm not sure I understand the OP. On the K-x, the only designation of the focus point in a finder is in Live View. The setting of the focus point for the optical finder does not even pretend precision.

Marc Sabatella used to explain this frequently here to new users of autofocus, but even in viewfinders where there are precise-looking dots showing the autofocus point, the actual point of focus is only approximated. AF systems tend to lock in on high contrast edges which allow their systems to work, and those points may or may not be exactly where the screen point indicates. Some strategy is needed to make autofocus work, and it would help to know that the scene is which is causing problems for the OP.
11-19-2010, 06:28 AM   #6
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QuoteOriginally posted by causey Quote
The focusing points one can see in the viewfinder (although they aren't luminous in K-x) correspond to regions of the sensor. But I'm not sure what you mean by "focusing points"... The dots marked on the viewfinder of your camera?
In my posts focusing points = focusing regions.

The lack of AF illumination on K-x does not bother me too much (as I bought camera already knowing about them).

The focus area misalignment - does bother me, as it indicates not so great workmanship. If this is just accident, I could possibly swap the k-x and get better tuned one. If it is general quality of the product - then there is no reason for swapping as I may get one that is worse. So far I did not discover anything very bad within this camera, and I would like to keep it. I like the little k-x.

If the whole issue lies only with the focusing screen alignment (this is what I'm trying to figure out), then it may be a cheaper for me to bring it to the local photo-camera repairer for alignment, than to send it to Pentax in UK (in the insured post) for warranty service.

Cheers,
elg (Erika)
11-19-2010, 06:34 AM   #7
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QuoteOriginally posted by GeneV Quote
Marc Sabatella used to explain this frequently here to new users of autofocus,
How I miss Mark. He was a saint of patience.
I tend too easily to rage after reading this sort of issue for about the 1000th time.
11-19-2010, 06:36 AM   #8
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QuoteOriginally posted by rawr Quote
How I miss Mark. He was a saint of patience.
I tend too easily to rage after reading this sort of issue for about the 1000th time.
I was gone for a month due to an accident, and he disappeared. Do you know what happened?

11-19-2010, 06:39 AM   #9
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How much shift is there, say, in units of the center ring diameter? Also, even a rough sketch of your test setup would help us to comment this on an intelligent basis.
11-19-2010, 06:44 AM   #10
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QuoteOriginally posted by elg Quote
In my posts focusing points = focusing regions.

The lack of AF illumination on K-x does not bother me too much (as I bought camera already knowing about them).

The focus area misalignment - does bother me, as it indicates not so great workmanship. If this is just accident, I could possibly swap the k-x and get better tuned one. If it is general quality of the product - then there is no reason for swapping as I may get one that is worse. So far I did not discover anything very bad within this camera, and I would like to keep it. I like the little k-x.

If the whole issue lies only with the focusing screen alignment (this is what I'm trying to figure out), then it may be a cheaper for me to bring it to the local photo-camera repairer for alignment, than to send it to Pentax in UK (in the insured post) for warranty service.

Cheers,
elg (Erika)
The focus screen you see in the optical viewfinder has nothing to do with autofocus. Is the problem that the area you expect to be in focus does not appear in focus on the screen or that it is not in focus in the photo?

I assume that by "focus region" you mean the approximate location in relation to the viewfinder markings that are indicated by the screen that sets the location of the focus point, or is that not what you mean? It would be helpful to see what the scene is which you are using to test. There are so many things that could play into a perception that the focus point or region is not properly located, or it could be actually misaligned.

I personally only use the center location for focus because it is too easy to forget the previous setting in the absence of viewfinder indicators.
11-19-2010, 06:51 AM   #11
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QuoteOriginally posted by jolepp Quote
How much shift is there, say, in units of the center ring diameter? Also, even a rough sketch of your test setup would help us to comment this on an intelligent basis.
It is 1/3-1/2 (definitely no more than 1/2) of the total width of the area between the round brackets in the viewinder.

The set-up: a little equal armed cross made from the dark brown sticky tape glued on the uniform color wall. Shooting from about 2 meter distance (orientation - landscape). Camera cannot focus on the wall, because of the lack of contrast and visible texture (but it can focus on the cross).
I will try to post sketch from home later today.

Last edited by elg; 11-19-2010 at 06:58 AM.
11-19-2010, 07:18 AM   #12
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With center focus, the focus area is about the size of the etched round brackets; see https://www.pentaxforums.com/forums/pentax-beginners-corner-q/89543-out-focus...o-anymore.html (post #9)

In which case the camera can decide to focus on anything inside it, not necessarily what you assume.
11-19-2010, 07:34 AM   #13
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How did you conduct your test? Did you select, say, a focusing point in the right area of the viewfinder, then used on a target? What kind of light did you have?
11-19-2010, 07:36 AM   #14
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And what happened to Marc?
11-19-2010, 07:45 AM   #15
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QuoteOriginally posted by sterretje Quote
With center focus, the focus area is about the size of the etched round brackets; see https://www.pentaxforums.com/forums/pentax-beginners-corner-q/89543-out-focus...o-anymore.html (post #9)

In which case the camera can decide to focus on anything inside it, not necessarily what you assume.
I'm not clear on whether her problem is the location of the focus points inside the brackets or that the K-x will focus on her target when it is outside the brackets.
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