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11-19-2010, 07:43 PM   #31
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The screen can't mis-align as it snaps into a recess. My guess is the phase detect module can be positionally adjusted slightly and if you send it in, they will probably try to move it slightly. This will change where the sensors read relative to the screen markings. Since the path distance from the beam splitter hasn't changed focus accuracy shouldn't change. But the techs should check this out as part of their repair.

Send it back if it bugs you. Or, use it until a month before your warranty expires and then send it in. They'll give it all a once-over and return it with a pristine sensor, too.

11-19-2010, 08:24 PM   #32
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I did the test with the center focus region and a variety of objects against solid colored walls and a ceiling. I didn't make any crosses or dot, but the objects tended to be more like the dot than the cross. I did the test at various distances so that the objects of different sizes filled the focus region to different degrees.

The results were very simple to report: if any part of the object was inside the center circle on the focus screen, focus quickly locked. It did not matter whether the object was in the center or edge of the circle. As soon as the camera was moved so that the object was completely outside the circle there was no lock. The circle seemed to be quite precise in showing me the outer limits of the area in which the target must be. However, within that circle, the target could be anywhere.

This is consistent with how I have used the K-x through its 10,000 actuations. I have always assumed anything within the circle is a possible lock and deal with DOF accordingly, or use the center circle to make sure I have locked focus on an object in the plane of my desired point of focus before composing.
11-19-2010, 08:51 PM   #33
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QuoteOriginally posted by DonP Quote
... Or, use it until a month before your warranty expires and then send it in. They'll give it all a once-over and return it with a pristine sensor, too.
For some reason I like this idea, DonP. Maybe because the other things then can be fixed too (if my k-x has them, of course, which can be discovered during that period).

Cheers,
elg (Erika)
11-19-2010, 09:00 PM   #34
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QuoteOriginally posted by GeneV Quote
However, within that circle, the target could be anywhere.
Gene,

During focus on dot checks (The smaller the dot, the more precise the check) I discovered that the central AF sensor is, most likely, really cross-shaped. So the central focusing sensor does not occupy the whole central area uniformly (even if it is not shifted, like it is on my k-x).

Cheers,
elg (Erika)

11-20-2010, 06:32 AM   #35
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QuoteOriginally posted by elg Quote
Gene,

During focus on dot checks (The smaller the dot, the more precise the check) I discovered that the central AF sensor is, most likely, really cross-shaped. So the central focusing sensor does not occupy the whole central area uniformly (even if it is not shifted, like it is on my k-x).

Cheers,
elg (Erika)
I tend to do tests that approximate my own practical use, whether it is of a lens or camera rather than creating targets and tests which may actually be more scientific, but less like my use. I was looking for items that would be the smallest things I would reasonable expect to use to lock focus at various distances. Targets included cabinet or door hardware, an electrical switch, a wire, a screw head in a white wall (probably the most precise), etc. Light was tungsten or flourescent since it was evening.

I did not test for a cross pattern but may try and check that out. I suppose one could try an object at 1 o'clock, 2 o'clock, etc. to see exactly where the field is, but that might not matter much for how I personally use the camera. I need only know that a particular area is sensitive and I will use that area. However, as far as I could see, if any object put so much as its toe in the water of the central region, it was locked. For example, a black wire against an off-white background could extend from the edge of the finder to the edge of the circle, but until the tiniest bit of it crossed the line of the circle, it would not be locked. If the screw head was anywhere I tried in the circle, it was locked.

FWIW, Erika, I am left with two possibilities to suggest for your K-x. My K-x does not seem to have an unacceptable focus pattern. Either there is something wrong with yours, and you should do as Don suggests (nothing to lose but some postage and time) or your test is so precise (perhaps because of the size and shape of the target) that it is outside of the practical limits for which the camera was designed. I think you'll never know which unless you give the Pentax folks a shot at the body.

I have found the K-x focus to be more than acceptable if the focus point is locked on the center. However, since I am comfortable with shifting to MF in my DSLR bodies when I want high precision, my expectations of AF point accuracy may be lower.
11-20-2010, 06:40 AM   #36
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QuoteOriginally posted by elg Quote
During focus on dot checks (The smaller the dot, the more precise the check) I discovered that the central AF sensor is, most likely, really cross-shaped.
...
In fact it is supposed to be a cross type sensor. My understanding is that this means it is composed of two linear sensors at right angles to each other. It seems you have evaluated it quite thoroughly :-)
11-20-2010, 12:13 PM   #37
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QuoteOriginally posted by jolepp Quote
In fact it is supposed to be a cross type sensor. My understanding is that this means it is composed of two linear sensors at right angles to each other. It seems you have evaluated it quite thoroughly :-)
It also tells me that her dots are very small.

I just repeated my test using a dark, round screw head a little larger than the pupil of an eye on a white wall. I stepped back to the point where the center circle diameter was about ten times the diameter of the screw head, and the area did not yet react as a cross. The presence of the screw head anywhere in the circle, even off 90 degrees, such as at 1 or 2 o'clock at the edge of the circle, would lock.

To put this in more practical terms with the FA77 mounted, a pupil (at indoor size) anywhere within the center circle at 16' feet (as far as I could step back) will lock focus, and I did not find the limit at which this pattern changed from a circle to a cross. On the other hand, the circle on my K-x was very accurate with the target I was using.

Last edited by GeneV; 11-20-2010 at 01:18 PM.
11-20-2010, 02:08 PM   #38
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I attempted to exchange the camera in the shop today. This did not work out. According to them - as long as camera takes pictures and does not have any immediately obvious problem (like a crack on the viewfinder, or the camera body, or broken focusing motor), then it is considered not faulty. Even talking to a manager did not help. That's probably because they are not specialized photography shop (I bought it from Argos - they sell stuff through the catalog).
Anyway, I will have to write directly to Pentax representatives then, and see what they will say.

Cheers,
elg (Erika)

11-20-2010, 03:08 PM   #39
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QuoteOriginally posted by elg Quote
I attempted to exchange the camera in the shop today. This did not work out. According to them - as long as camera takes pictures and does not have any immediately obvious problem (like a crack on the viewfinder, or the camera body, or broken focusing motor), then it is considered not faulty. Even talking to a manager did not help. That's probably because they are not specialized photography shop (I bought it from Argos - they sell stuff through the catalog).
Anyway, I will have to write directly to Pentax representatives then, and see what they will say.

Cheers,
elg (Erika)
Many shops like that leave it to the manufacturer for any warranty work. It will be interesting to see what Pentax does with it.
11-21-2010, 03:22 PM   #40
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I e-mailed to Pentax repair center (the one in UK) describing the issue. I included some ilustrations similar to the ones I posted here. I asked them is such camera focus points behaviour within acceptable Pentax calibration/tuning limits, or would they advice me to send it in for servicing. I hope they will reply within a few days.

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elg (Erika)
11-25-2010, 06:11 AM   #41
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Still no reply from Pentax repair center.
In addition to this Yesterday I posted a query to Pentax technical support (online - from Pentax UK website).

btw. I recently got DA 35mm F2.4. Nice lens though it seems to back-focus in daylight, but it is nearly OK under tungsten. Kit lens seems to be in reverse - visible FF under tungsten (tested when shooting close objects) but looks ok-ish under daylight. I need to do more precise checking on these FF/BF issues though.

Can these perceived FF/BF issues be related to the wrongly calibrated K-x body (and dislocated focus 'points'), or are they more specifically lens issues?

What I can say... so far I'm unimpressed by Pentax QC.

Cherrs,
elg (Erika)
11-25-2010, 07:11 AM   #42
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QuoteOriginally posted by elg Quote
...
Can these perceived FF/BF issues be related to the wrongly calibrated K-x body (and dislocated focus 'points'), or are they more specifically lens issues?
...
They seem to be both: the fancier bodies have AF adjust settings for different lenses (+ one global setting). One would assume that one setting would be sufficient to compensate for AF sensor / focus plane (capture sensor) being off in relation to each other but apparently there is something more to it than is immediately obvious. BTW the k-x has one global adjustment available trough the debug menu (see: RiceHigh's Pentax Blog: K-x Debug Mode Activation Method)
11-26-2010, 08:48 AM   #43
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Thanks, jolepp.

I got answer from Pentax tech support (but not from the Pentax repair services). Tech support suggested using focus test chart for focus test, and if I'm not happy about it after the testing then to contact the Pentax repair services (as I complained to them not only about shifted focus points, but about possible miss-focusing issues as well).

I'm just wondering if one sends camera for warranty services, should it be included in original packaging (with all the CD's, cables etc.), or is it sufficient to send the camera and lenses only?

I'm going to run some focus tests over the weekend. Next week I probably will send the camera in (even if focusing will turn out to be acceptable, because focus point shit is annoying me).

Cheers,
elg (Erika)
11-26-2010, 11:45 AM   #44
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QuoteOriginally posted by elg Quote
Thanks, jolepp.

I got answer from Pentax tech support (but not from the Pentax repair services). Tech support suggested using focus test chart for focus test, and if I'm not happy about it after the testing then to contact the Pentax repair services (as I complained to them not only about shifted focus points, but about possible miss-focusing issues as well).

I'm just wondering if one sends camera for warranty services, should it be included in original packaging (with all the CD's, cables etc.), or is it sufficient to send the camera and lenses only?

I'm going to run some focus tests over the weekend. Next week I probably will send the camera in (even if focusing will turn out to be acceptable, because focus point shit is annoying me).

Cheers,
elg (Erika)
It shoud not be necessary to send the CD and cables for repair. I do like the packaging for any shipping, though.
11-26-2010, 11:51 AM   #45
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QuoteOriginally posted by GeneV Quote
It shoud not be necessary to send the CD and cables for repair. I do like the packaging for any shipping, though.
What I meant was original packaging. I could wrap things well into bubble material and put them into ordinary box for postage, as opposed to wrapping them, putting them into original box, and then putting that box into another box.

Some warranty services require original packaging (Perhaps in order to be sure that serial numbers match).

Cheers,
elg
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