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11-19-2010, 07:58 AM   #16
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If you do a search of the forum from about a year ago, Erika, you will find several posts where this subject has been discussed. There is even a post where one member had plotted where the auto-focus points were in his/her k-x. I do remember seeing them as being shifted both UP and to the right of where they are depicted in literature for that user's camera. I also don't think this is indicative of any workmanship problems. Consider the geometry and beam splitting the light. Microns of difference can mean fractions of mm changes in where the focus point appears to be located.

Another thing to consider regarding the size of the focus point is you'll probably find it easier to have the camera focus on what you want. The center cross focus point in my old Nikon D40 wasn't located exactly where the LED lit, It took me awhile to realize that after looking at many shots - especially portraits where the eyes were not in focus, but maybe the nose was. I know where the focus zone is on my k-x and it's second nature now to use the offset, focus and recompose. And the focus locks and doesn't hunt. My D40 would sometimes hunt because it was trying to focus on a cheek with almost no contrast or texture.

I'm sure those who shoot macros rue the lack of focus point illumination and the size of the focus zones. They are not where you think they are and they are larger. It makes it tough to get the fly's eyes tack sharp. But for the rest of us that shoot everyday life and landscapes it a is a non-issue. Changing bodies may or may not help. If you can't enjoy your k-x you best option may be to shift it. I love mine, warts and all.

11-19-2010, 08:15 AM   #17
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QuoteOriginally posted by elg Quote
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.
This is normal. AF points is the marketing name, but are not really points.

QuoteOriginally posted by elg Quote
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
If I understand what you're saying, maybe it's the focusing screen which is misaligned, so it's not matching exactly with the AF position. You should return if it bothers you, as I expect you have warranty.

To tell the truth, though, I don't believe I would be able to detect this problem even if I looked after it. If your camera is working and focusing, I wouldn't bother.
11-19-2010, 08:42 AM   #18
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QuoteQuote:
And what happened to Marc?

You could probably PM him and ask. I think he got burned out on answering the question 1,000 times :-) And he was frequently the first to respond.

According to his blog, he is in Denver hosting a jazz workshop.

Last edited by SpecialK; 11-19-2010 at 08:47 AM.
11-19-2010, 08:43 AM   #19
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QuoteOriginally posted by causey Quote
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?
Initially I used the central point only. When I noticed that it is 'dislocated' I used other points in rotation (one at a time), to find out are they 'dislocated' as well. They were. The light was tungsten.
It was not about the precision of the focus, front-focus or back-focus. It was about the camera focus confirmation for the active focus point, in order to determine where that focus point is located on the viewfinder (and what its approximate size is).

Cheers,
elg (Erika)


Last edited by elg; 11-19-2010 at 09:01 AM.
11-19-2010, 08:47 AM   #20
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QuoteOriginally posted by SpecialK Quote
You could probably PM him and ask. I think he got burned out on answering the question 1,000 times :-) And he was frequently the first to respond.
I PM'd another mod who tells me Marc tells them he is extremely busy at his teaching. I notice on his blog that he is in the middle of conducting a workshop this week.
11-19-2010, 08:47 AM   #21
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QuoteOriginally posted by elg Quote
Initially I used the central point only. When I noticed that it is 'dislocated' I used other points in rotation (one at a time), to find out are they 'dislocated' as well. They were. The light was tungsten.
It was not about the precision of the focus, front-focus or back-focus. It was about the camera focus confirmation for the active focus point, in order to determine where that focus point is located on the viewfinder (and what its approximate size is).
So, you used the central focus point, and the camera focused correctly... The focus was precise. Then how did you determine focus points were misaligned? By the way you got the luminous focus confirmation? But how, exactly?
11-19-2010, 08:52 AM   #22
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QuoteOriginally posted by GeneV Quote
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?
No, it is more related to the finding, that the actual focus point in the viewfinder is not where I expected it to be.

QuoteOriginally posted by GeneV Quote
I assume that by "focus region" you mean the approximate location in relation to the viewfinder markings
Yes.
For example, I expected the central point to be roughly (but not necessary precisely - maybe shifted very slightly to one or other direction) in the middle between the round bracket markings, but not shifted by 1/3-1/2 of the dimension (of the central area) to the right.
11-19-2010, 09:11 AM   #23
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To me it seems that OP's method of determining the actual location of the focus points is sound. Also, given the precision with which the AF sensor (& light path components) must be located relative to the sensor plane for AF to work properly and the amount of play that there could be with the (stock) focus screen, 1/3 of the central circle diameter sounds like too much to be in spec.

@OP: Does the focus screen center circle appear to be in the middle of the frame (in captures and otherwise)? Is AF in fact precise?

11-19-2010, 09:31 AM   #24
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QuoteOriginally posted by jolepp Quote
To me it seems that OP's method of determining the actual location of the focus points is sound. Also, given the precision with which the AF sensor (& light path components) must be located relative to the sensor plane for AF to work properly and the amount of play that there could be with the (stock) focus screen, 1/3 of the central circle diameter sounds like too much to be in spec.

@OP: Does the focus screen center circle appear to be in the middle of the frame (in captures and otherwise)? Is AF in fact precise?
I agree, i don't know why folks are discouraging the op from sending it in. The size of the area is not an issue, the size of this misalignment is, whether its due to the screen or the focus device, is irrelevant.

i hope the op reports back after sending it in. It would be interesting to know how effective the repair is.

Best wishes,
11-19-2010, 10:15 AM   #25
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QuoteOriginally posted by causey Quote
So, you used the central focus point, and the camera focused correctly... The focus was precise.
I did not say that. To be precise - camera clearly front-focuses under tungsten. But this test was not about this. It was about where the focus point is actually located on the viewfinder.

QuoteOriginally posted by causey Quote
Then how did you determine focus points were misaligned?
With the central point enabled camera refused to focus on the little cross when that cross was roughly on the middle of left round viewfinder marking. It did focus on it when the cross was on the middle of the right round viewfinder marking, and even when it went more to the right - completely beyond the right round marking border.
When doing this I did not take the pictures or checked how sharp looks the image in the viewfinder (the little cross was too small for this particular purpose). I was checking am I getting focus confirmation from camera or not.

Sorry about the confusion.

QuoteOriginally posted by causey Quote
By the way you got the luminous focus confirmation?
Focus confirmation was the usual beep and lit green hexagon.

Cheers,
elg (Erika)
11-19-2010, 10:28 AM   #26
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QuoteOriginally posted by philbaum Quote
I agree, i don't know why folks are discouraging the op from sending it in. The size of the area is not an issue, the size of this misalignment is, whether its due to the screen or the focus device, is irrelevant.

i hope the op reports back after sending it in. It would be interesting to know how effective the repair is.

Best wishes,
I don't think people are discouraging her from getting it checked out. She is asking for advice from this forum, and people are requesting information in order to be helpful. I suppose everyone could have just said "send it to Pentax" and been done with it.

I, too, would be interested in how effective sending it back would be, since Sterretje linked to another thread where some posters indicated that the level of accuracy she is experiencing may be typical--i.e. within the center marks is as close as it gets. I have never tried this out on my K-x in the manner described here.
11-19-2010, 01:42 PM   #27
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This is a rough illustration what I was talking about.

When central AF pont is selected, then:

In the first image (from the left - cross is on the left side) - camera fails to focus.
In the second one it focuses normally
In the third it can still focus
and in the fourth one it does not focus again.

The same experiment was done for a few other focus 'points' and I found all of them 'shifted' to the right.
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11-19-2010, 01:55 PM   #28
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QuoteOriginally posted by DonP Quote
If you do a search of the forum from about a year ago, Erika, you will find several posts where this subject has been discussed. There is even a post where one member had plotted where the auto-focus points were in his/her k-x.
Thanks, DonP,
I'm looking for these posts right now. So far I could not find them (there are a lot of topic's about k-x!).

QuoteOriginally posted by DonP Quote
Consider the geometry and beam splitting the light. Microns of difference can mean fractions of mm changes in where the focus point appears to be located.
This may explain the issue.

QuoteOriginally posted by DonP Quote
I'm sure those who shoot macros rue the lack of focus point illumination and the size of the focus zones.
I like shooting some macro style pictures as well (not to the level where focus on fly eyes becomes important though). The lacks of AF illumination does not bother me too much, but the very big focus 'points' may (or may not) pose some problems.

No camera is perfect. I like the little k-x (this is why I bought it), but at the same time I'm a little bit worried about these mis-allignment issues.
11-19-2010, 07:05 PM   #29
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QuoteOriginally posted by elg Quote
This is a rough illustration what I was talking about.

When central AF pont is selected, then:

In the first image (from the left - cross is on the left side) - camera fails to focus.
In the second one it focuses normally
In the third it can still focus
and in the fourth one it does not focus again.

The same experiment was done for a few other focus 'points' and I found all of them 'shifted' to the right.
I just did the same experiment with mine. I used center point and selectable AF points, and tested against a dot in a white wall.

I can't reproduce the same behaviour, mine stops locking focus as soon as the dot moves outside the center circle. Same happens with other selected points, if I move outside the brackets, it doesn't lock anymore.

It may be that your focusing screen is a little misaligned, if it bothers you should return it, at least mine doesn't exhibit so much misalignment as in your images.
11-19-2010, 07:28 PM   #30
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QuoteOriginally posted by hcarvalhoalves Quote
I just did the same experiment with mine. I used center point and selectable AF points, and tested against a dot in a white wall.
I did a quick re-test with the dot instead of little cross (as dot is smaller after all, so it should give more precise results) . It looks like the camera focused (in the case with cross) on the arm of the cross which is closest to the center. So with the dot this is as follows.

Camera fails to focus:
for the first image - inside the round center focusing bracket marks
(about the same as far right point of the right cross arm in the first image).
and slightly outside the round focusing bracket marks for the last image (about the same as far left point of the left cross arm in the last image).

It still results into the same conclusion - focus 'points' are shifted about 1/3-1/2 of the central portion width towards the right. Test with the point makes me think that the focusing sensor size may be a bit smaller though.

Thanks for the input.

Cheers,
elg (Erika)
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