[Marc Sabatella]

@Marc: in the previous posts I referred to a front-focus. Now such definitions are in the same league as stating 'the bridge is open', or saying 'sitting in front of the PC' versus 'sitting behind the PC'. I meant to say that the sharpest point in view was further away from the lens than the point-of-aim, thus 'more in front'. In all other posts that means back-focus so I'll switch to that point of view then

I wasn't quibbling about whether your problem is front or back focus. I was questioning whether your testing is sufficiently well-conteolled to be sure you have an actual hardware problem as opposed to the simple testing error that probably accounts for 90% of the reports of front or back focus seen here. Your use of the term "point-of-aim" suggests that, as with most initial attempts at testing focus, yours will turn out to be flawed as well, since it is not about where you aim but rather where the camera chooses to focus. There is nothing you can do about the latter, but FF or BF only exist if focus is somehwere other than where the camera chose to focus - which can and often is somewhere other than where you aimed.

[RKKS08]

@ HoBykoYan

"am not a techie person..."

If you are using MS-Windows, you may be using it with the default settings, meant to behave fool-proof for beginners. With these settings, any MS-program (including the explorer) does not show the true extension. And every MS-program on saving a file automatically adds an extension suitable for the program you use. So the name of the debug file may have a trailing ".txt" extension without showing to you. But the camera now will not find the file.

[mgvh]

Like the OP, I was having issues sometimes getting as sharp as shots as I wanted. I eventually found my way to the ricehigh blog with the means of adjusting backfocusing. I have tried quite a few different tests, including the Moire Fringe pattern. In every instance it seemed that back-focusing was the issue. Using the debug procedure and a bunch of trial and error, I eventually settled on +130um. I'm not sure how clear it shows in the attached pic, but at 100% it is clear that the adjusted focus pic is much sharper at the center.
The pics were taken at f5.6 at 6' which means a total DOF of about 2.7".
Pic on left @ 0um; pic on right @ +130um
Focus point is the red thunderbolt in the O of Rayovac

[HoBykoYan]

@ HoBykoYan
If you are using MS-Windows, you may be using it with the default settings, meant to behave fool-proof for beginners. With these settings, any MS-program (including the explorer) does not show the true extension. And every MS-program on saving a file automatically adds an extension suitable for the program you use. So the name of the debug file may have a trailing ".txt" extension without showing to you. But the camera now will not find the file.

Hi RKKS08,

How could I address this issue with the txt thing?

[HoBykoYan]

@HoBykoYan: from the Ricehigh blog above it is clear that it works from any K-x firmware version to date, I have 1.02, perhaps you can try to upgrade first?
Can you define what you see when you switch on the camera? Did you make sure you hit [ENTER] when typing the line in de modset-file; the cursor needs to blink on the next line when you save it...

Hi Twarp. Yes i made sure that the cursor is at the bottom blinking. thanks
Still not working though

[mgvh]

Hi RKKS08,

How could I address this issue with the txt thing?

Why don't you just download the file that ricehigh provided on his web site?

If you don't know how to create the file, simply Download it Here, for the file I created.

[HoBykoYan]

YESSSSS!!!

finally made it...
You're right RKKS08 there is an extension MODSET.494.txt instead of MODSET.492 only (checked the properties...)
Thanks everyone...

Now here comes another problem
im using a DA 16-45mm lens
@ 16mm correction +180 and
@ 45mm correction -120
do i need to change the correction everytime? i think ther's no problem with primes here though but i have to take not the correction number for each lens that i would be using now with my K-X...

I think need to upgrade body or do correction everytime....

[Twarp]

@ HoBykoYan
If you are using MS-Windows, you may be using it with the default settings, meant to behave fool-proof for beginners. With these settings, any MS-program (including the explorer) does not show the true extension. And every MS-program on saving a file automatically adds an extension suitable for the program you use. So the name of the debug file may have a trailing ".txt" extension without showing to you. But the camera now will not find the file.

Ouch, why didn't I think of this, working in ICT troubles your mind I guess

@Marc, I don't mind you questioning my train of thought considering trying to find a solution to a (sudden, it used to be good, that's the weird part) blurry focus problem. I have been running over and over the actions involved in focusing, why and how. At the moment I select the central focus point I think I may rule out that the camera randomly chooses another of the 10 remaining focus points. The K-x has no red dots to represent the focus points but from other posts I understand that they are only indicators and in several documented cases do not coincide with actual focus points (like a misplaced overlay). Therefore I assuming these 11 points are fixed area's however there is no way of knowing where they actually are, except for the central one:
As a quick test I put a number of empty film cannisters and sugar cubes at 1/2m interval on the floor and when aiming the center of the viewfinder at them respectively, the focus changed accordingly. Thus I assume that the selected central focus point in the viewfinder coincides with the actual center of the screen which then may be used to 'aim'. If the actual aimpoint would have been off-center, one could adjust accordingly. Just like you would do with misaligned sights on a gun. Please let me know whether I make a mistake here or leave something critical out of the calculation.

I actually shot a brick wall from ca. 1m distance, the lens parallel to the surface. In this case, no matter what focus point the camera would have chosen, without correction no total sharpness could be achieved with AF. A correction of +130um gives best=sharpest results with this lens/camera combination. This is repeatable in different circumstances (daylight/artificial light, different targets and distances, etc.). The pictures of mgvh perfectly show what I found as well, coincidentally with the same correction.

[Marc Sabatella]

@Marc, I don't mind you questioning my train of thought considering trying to find a solution to a (sudden, it used to be good, that's the weird part) blurry focus problem.

As I've said before, if the placebo effect is string enough for people to perceive a lessening of symptoms and indeed even increase the rate of spontaneous cures (which it is) after being given a sugar pill, then it's certainly strong enough to make one believe one's lens has developed a problem after some random event causes them to notice things that have been true since day one.

I'm not saying that there is no chance your lens has somehow spontaneously developed a problem - a problem for which there is no known physical phenomenon that possibly produce the alleged results. But I am saying that the act that it *seems* the problem just started doesn't surprise me; that's not even the least bit uncommon. The normal operations of AF are such that there is always the chance that the camera will choose to focus somewhere other than you expect. At first, you write off such occurences as random, but at some point, you become convinced there is a problem, and then you start noticing it everywhere. It's a story that has been repeated here and elsewhere hundreds of times. So I personlly would put zero stock in the perception that the something has changed recently; that's an almost completely unreliable perception and impossible to test for since you don't have a time machine to allow you to perform controlled comparisons.

So, step is to try to regain objectivity in your testing and focus on what can actually be tested: performance *now*.

At the moment I select the central focus point I think I may rule out that the camera randomly chooses another of the 10 remaining focus points. The K-x has no red dots to represent the focus points but from other posts I understand that they are only indicators and in several documented cases do not coincide with actual focus points (like a misplaced overlay).

No, not like a misplaced overlay. It's just a simple matter of size - the red dots are much smaller than the actual focus sensors. The camera can and will often focus on an object that is not directly under the red dot.

I assume that the selected central focus point in the viewfinder coincides with the actual center of the screen which then may be used to 'aim'. If the actual aimpoint would have been off-center, one could adjust accordingly. Just like you would do with misaligned sights on a gun. Please let me know whether I make a mistake here or leave something critical out of the calculation.

Well, you are undoubtedly correct that the actual center of the viewfinder is somewhere within range of the central focus sensor. However, you still uave not ascertained the complete range of that sensor. That's a useful experiment as well, and the same setup should prove useful - just keep trying to focus on an object while moving the camera to put it increasingly off-center.

I actually shot a brick wall from ca. 1m distance, the lens parallel to the surface. In this case, no matter what focus point the camera would have chosen, without correction no total sharpness could be achieved with AF. A correction of +130um gives best=sharpest results with this lens/camera combination. This is repeatable in different circumstances (daylight/artificial light, different targets and distances, etc.). The pictures of mgvh perfectly show what I found as well, coincidentally with the same correction.

Assuming you really were perfectly parallel (how did you measure this?), then yes, that's a pretty good test result. I'd just observe that there is no known physical phenonemon that would cause the *lens* to have any involvement in that if you test was really as exhaustive as you say - and in particular, if you tried testing with the initial focus point at infinity and also at minimum. If the focus is consistently off, then there is one and only one very simple physical explanation: the focus sensor within the camera is not at the same distance from the lens as the imaging sensor. People have theorized about possible ways the lens could be involved - suppositions about the gearing ratio of the focus screw being off, or residual CA that causes the focus point to change as you stop down. If either of those were the case, though, your focus discrepancy would not be consistent at all. If it were something in the gearing, you'd get different results dependning on where the initial focus point was. And if it were residual CA, you'd only see an issue as you stopped down (and it wold become difficult to see since DOF would mask it).

[Twarp]

This is a very interesting discussion. If I just admit I've been using a placebo, then I should undo the correction and proceed in my daily routine. - Of course there was no problem after all and all pictures will be sharp, as they used to. I was just creating and exagerating my own problem by experimenting with the AF-correction settings -.

Now this was not the situation. I only found out there was an AF-adjustment possibility after I went searching for AF-trouble. Moreover, I do not think there's something wrong with any of the lenses but that the problem is somewhere in the camera itself. The suggestion that the focus sensor changed its relative distance from the lens whith regard to sensor-lense distance remaining constant, sounds most likely to me. Perhaps it's loose or shifted which could explain why it happened 'suddenly'. Perhaps even the other way: the total shake reduction platform shifted position and the focus sensor is still fixed. I don't believe in gearing ratio's and residual CA as the cause for these problems.

Is there any technical paper or drawing available, explaining how the AF-mechanism works? Now I'm becoming curious of how big the sensor area's are and how they are interspaced, if they do overlap or just touch or leave blank spots in between. In any case the K-x leaves the user oblivious of how focus has been achieved, 11-points, 5-points or spot focus. Don't even know where the spots are supposed to be except for the center-one.

When the weather clears over here I'll try to take some bright distance pics and also try to experiment with very close focussing and focus area determination. Different AF-modes, different lenses. Hopefully this weekend or so. And give the camera a shake-up beforehand and see if AF changes...

[Marc Sabatella]

I don't know of any technical specs, but it's easy enough to see for yourself how big the focus sensors are - just select a focus sesnor and then try to focus on a black dot on a piece of white paper with the dot in a variety of different positions. If ipthe camera can focus, then the dot is in range.

As for my comments about placebo effects and so forth, understood that I started out talking very generally, as your initial posts didn't really contain enough evidence to suggest that you had controlled your experiment well. I think by now you should have a pretty good deal of confidence that the AF sensors in your camera are indeed misaligned by an amount such that your adjustment works around it.

[stevebrot]

There is no way to know which line the camera tried to focus on - it isn't necessarily the one directly under the red dot for the focus point you have selected. Those red dots are just approximations. The camera can legitimately choose to focus anywhere in general vicinity of that red dot.

Bottom lime: your test is invalid. Chances are, thee is no problem at all, and it's just faulty testing methodology fooloing you into thinking thee is a problem. It is much, much easier to conduct a completely bogus focus teat than to do it right.

Feel free to post same images and we'll probably be able to explain how and why the camera is simply choosing to focus somewhere other than where you intended, and how you can take steps to make the camera focus focus where you want. But thee is practically zero chance that this is a lens problem based on your description.

What he said.

I cannot count the number of threads I have read on this site where the user complains about front/back focus and where the setup to test is the primary culprit. The best way to test focus accuracy is to use a moire-based test target mounted on a flat board arranged parallel to the plane of focus and a series of exposures +/- that of the camera-chosen point of focus.


Steve

[Marc Sabatella]

I would say that his followups have increased my confidence that his camera (not lens) is slightly out of alignment.

[jatrax]

28 posts and no one noticed the original post is from about 15 months ago? Wonder what the OP ever did? Looks like he got a lot of good advice, but maybe too late to return under warranty now.