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06-26-2008, 08:37 AM   #16
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QuoteOriginally posted by konraDarnok Quote
I'm inclined to trust my eyes. Full pixel crops:
...
I, and others, have backfocus issues with their K10D. The Debug setting fixed my issue just fine -- with all lenses (except a teleconverter problem I'm having)
I don't mean to question that some people genuinely have problems, but some people are guilty of assuming a small population sample has a defect to be indicative that ALL units have defects, which is as invalid a conclusion as my not having any problems indicates that there NO problems with any units.

I'm not suggesting that YOU(or other people who genuinely have problems) are saying that ALL units are defective, but there are some other people that don't understand how the statistical math works. In fact, I fall into that category, despite having 3 statistics classes. I just haven't done much statistical analysis after graduation.

Then there some people(again not you necessarily) who become convinced they have a defective unit because they read an article about it on the internet and one of the snapshots is blurry, when what they really needed was a tripod, or they needed to move closer and do less cropping and enlarging to end up with a 2MP file that they try to print at 8x10.

Again I emphasize that I'm not talking about you specifically, but I have dealt with people who complained to me about their 6MP camera being "broken" or not enough MP, when they had printed an 8x10 at a ridiculously low resolution because they kept cropping and resizing the image until it wasn't even half it's original size. And then they found an entry on someone's blog who did genuinely have a defective unit, so that must be the problem, eh?

06-26-2008, 09:09 AM   #17
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QuoteOriginally posted by brothereye Quote
2+2=5 for very large values of 2
Yes! I like this calculation (if this is critical)
06-26-2008, 09:31 AM   #18
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QuoteOriginally posted by k10dbook Quote
Were you still having the zig-zag lines when printed?
I did't print it.
QuoteOriginally posted by k10dbook Quote
I appreaciate your comments and will wait for additional comments to react. I wrote to Pentax and received an answer to my email. They are testing and reviewing the chart and will let me know their opinion, comments, approval...actually I'll have to see what their answer is. I will post it here when received. They were actually very appreciative for the charts and very nice.
Glad to hear that Pentax cares.

As for the additional comments...
You may want to do some own tests with non-perfect black and white. I always found it somewhat "sub optimal" that test charts use a scale far off the centre to verify focus (they have to, of course). However, not every lens will have an ideally flat focus plane. To be able to see the paper grain structure is reassuring. As would be a printer dot pattern from non-perfect colors. A black half, on the side, would be a step back from the horizontal-bar kind of chart.
06-26-2008, 06:19 PM   #19
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PART-2. Autofocus Adjustment for the Pentax K20D, AF accuracy check for all DSLRs.

HOW TO PERFORM THE TEST

Download the Charts here.

The two smaller charts were designed so that they can be cut and taped together in a way that they can stand at a 45° angle when placed on a table, desk, or flat surface. The camera / lens is then leveled and preferably positioned on a tripod so that the lens’ centerline is aligned with the center of the chart. Place the lens as close as you can to the center of the chart target while it can still focus on the intersection of the black / white section, then back it off just a little. Position the large chart flat (horizontally) and the camera / lens angled at 45° from the chart.

After choosing the chart that will work best with your lens, and once the chart and camera / lens are position correctly, start by trying to focus on the white area of the chart. The lens should not be able to focus correctly and it should be “hunting”. If it achieves focus while pointing to the middle of the white area, it means you could actually be in focus with the lines surrounding the white area and you need to use the next larger chart.

Next, move the camera / lens angle slowly downward until it auto focuses. At that point, you know that you are focused on the intersection of the black / white portion of the chart. That is the center of the chart. The measurements (Metric on the left and English on the right) are at zero on both sides of the chart horizontal centerline. Take the picture and look at the results. The center target line (00) should be perfectly clear while the top and bottom target lines and text should get increasingly and proportionally out of focus. The top target lines represent the back focus area while the bottom target lines represent the front focus area. Repeat this test several times to make sure you have done the test correctly. If the center target line is in focus, but the front and back target lines are not proportionally getting out of focus, there shouldn’t be any serious problems with the lens. Remember that this test is done with the lens opened at the maximum aperture and that the depth of field will increase with smaller aperture. Most of the lenses have a “sweet spot which is usually 1 to 2 stop smaller than the maximum aperture. Therefore, you should only be concerned if the center target line is not in perfect focus while either the back or front lines are.

UNDERSTAND THE RESULTS

The perfect lens should return a result similar to the image below:

A lens with acceptable Auto Focus should have the center target line in focus, even if the back and front focus lines are not equally or proportionally out of focus.

A lens with front focus problems will look like the image below while a lens with back focus problems will look like the image below it.

A WORD ABOUT AUTO FOCUS SENSORS

Sensors are either vertical, horizontal or cross type. Pentax K10D and K20D have 9 cross type sensors and two vertical sensors. Vertical sensors detect the sharpest vertical contrast within its area of coverage and lock the focus on that point. Alternatively, the horizontal sensors detect the sharpest horizontal contrast within its area of coverage and lock the focus on that point. You guessed it; the cross type sensors detect the highest vertical or horizontal contrast and lock the focus on that point. Since we use the center focus point of our camera, which is a cross type sensor, our chart was deliberately designed without any vertical lines in the center so that the focus can only lock at the intersection of the black and white portion of our target. Note that in your viewfinder, the little red square indicates the focus area but the cross sensor is not necessarily dead center. It merely shows you the area of the sensor, but is not an exact focus point as the sensor will lock on the point of maximum contrast.

DIFFERENCE BETWEEN 45° and 30° CHARTS

The above charts, one at 45° and one at 30°, illustrates why the depth of field is proportional to the angle of the chart. Notice that in all cases, the depth of field viewable area is the same for the front and back focus.

K20D CUSTOM SETTING NUMBER 35 – AF ADJUSTMENT

In the Custom Setting menu, navigate with the four-way controller to AF Adjustment, Setting number 35. Use ▲▼to turn the AF Adjustment On or Off. When choosing On, press ► and select if you want to adjust the lens attached or all the lenses. It seems that choosing all lenses would indicate that the camera needs AF Adjustment as choosing the current lens would adjust the AF for that lens when attached to the camera. The camera can retain settings for up to 20 lenses. Using the rear rotary dial, you can adjust the values from minus 1 to minus 10 and plus 1 to plus 10. You can reset the camera to the factory defaults anytime by navigating down ▼ to Reset and confirm Reset.

DISCLAIMER

Although the Charts have given me good results, you should fully understand how they help analyzing the Auto Focus accuracy. Read the above paragraphs several times until you completely grasp the procedures. You can adjust the focus of all Pentax lenses within the K20D, as they are non-permanent changes. You can reset the Auto Focus to factory defaults at any time. As for the other Pentax camera models, you should only have a Pentax trained technician adjust the Auto Focus of your lenses or DSLR cameras.

Thank you very much for reading,

More pictures are posted on my blogsite.

Yvon Bourque

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Last edited by ebooks4pentax; 06-27-2008 at 12:29 AM.
06-26-2008, 07:11 PM   #20
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If you don't like charts, and do not need to have precise dimension of what the front or back focus are, there is an even simpler solution, pointed out this week. It's the batteries test. Put batteries (at least 3 of them) in a 45 degree position. If your lens is a telephoto and cannot focus close enough, use Coke cans or bigger similar objects. Aim the center focus at the centered battery and see what is in focus. That's as simple as it gets.

I know it's not very scientific, but it can work.

Best Regards and thank you for reading,

Yvon Bourque
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07-03-2008, 12:48 PM   #21
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I tried tonight.
The downloaded Pantexian 45 degree chart in high contrast Black and White oval did not work well to me (especially at indoor MF). Also the lines and scale markings in "mm" were too small to be seen. Maybe better use texts in bigger Arial Fronts for the readability for a shot 2m away as well.

Also, I think the chart should have an distinguishable thick mild grey strap band in the middle and with certain text or texture inside the strap.

I tried also using some real objects for the setup. (middle in contrast and colors; not too extreme in contrast). I tested 2m always (normal application). The clamps in the middle is not blur now.
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Last edited by ckanthon; 07-03-2008 at 04:02 PM.
04-13-2010, 03:49 PM   #22
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QuoteOriginally posted by falconeye Quote
I always found it somewhat "sub optimal" that test charts use a scale far off the centre to verify focus (they have to, of course).
This is exactly my main gripe with this otherwise very thought out chart (as I mention in my AF adjustment hints).

One way around this problem would be to use a "dynamic" chart, i.e., use a flat target which is easy to focus on (some helpful pattern) and then replace this with a ruler-like measurement aid for the actual shot. The challenge with this "dynamic" chart is to make sure that the ruler zero line will always be exactly where the focus target has been.

I could imagine a rotating board which has the target pattern on one side and a ruler pattern on the other side with the axis running through the board so that both sides have the same distance to the camera. Of course, when using the ruler pattern, the board is tilted to a degree that is appropriate for the focal length in use.

Lazy people could add a remotely controlled actuator that flips the board for them.

EDIT: On second thought, the rotating board should really have three sides, one of which is a mirror to be used for aligning the camera before one uses the target side. A lot more difficult to realise as a DIY solution but perhaps not a bad idea in principle.
04-13-2010, 05:07 PM   #23
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I'm surprised to see my chart comments coming up to the surface after such a long time. Everything being equal, it is not necessary to read what is on the chart far left or right, it is importand to see that the center focus point is in perfect focus and that the chart equally goes from tack sharp to blurry, equally fron the front and back focusing chart. The charts are downloaded sometimes up to 400 times every day, and that by Pentax, as well as Canon and Nikon.

If you read the instructions that are included when downloading the chart, you will certainly understand why the process is important. You can still download the charts from my blogsite.

Best regards to all,

Yvon Bourque

04-13-2010, 10:39 PM   #24
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QuoteOriginally posted by k10dbook Quote
I'm surprised to see my chart comments coming up to the surface after such a long time.
The reason I commented was that I had this idea about a chart which has no issues with lenses that have a curved field of focus. I believe even though no one posted here for a while, the thread is still being used as a resource by silent readers and I just want to flag this potential issue.


QuoteOriginally posted by k10dbook Quote
Everything being equal, it is not necessary to read what is on the chart far left or right, it is importand to see that the center focus point is in perfect focus...
If that were the case only then focusing on a parallel target with a focus pattern would be much better.

QuoteOriginally posted by k10dbook Quote
... and that the chart equally goes from tack sharp to blurry, equally fron the front and back focusing chart.
Here lies the problem. In the middle area the chart does not allow you to judge sharpness well. In the outer area, the focus plane might be somewhere else than it is in the centre (due to field curvature of the lens). Since people will typically use the outer area to judge where the best point of focus is, they will adjust in a way that optimises the focus at the edges whereas they really should be optimising the focus for the focus target (centre).
04-13-2010, 11:01 PM   #25
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The focus center point, although marked by a red square in the viewfinder, is not necessarily dead center. The camera focuses on the nearest and sharpest contrast, hence the big circle with a clear delineation between the black and white. Even if the focus point is not dead center, the circle is big enough that the camera will have no other place to focus than the black/white delineation. At that point, you can judge which is the sharpest point, (being the actual focus point) and the front/back focus. It doesn't need to be tacky sharp, just enough so that you can pinpoint the clearest point and the fading point of the front/back focus.

If that is not convincing enough for you, focus on the center point with the camera, lock the focus and move the chart to the left or right while keeping the focus lock. Moving the chart is easily done by taping a ruler perpendicular to the camera and sliding the chart against it. As to make sure the camera is level with the center of the chart, just measure the distance from the floor or table to the center of the chart and the center of the lens. Geometrically, the chart is designed so that the oval is a perfect circle when viewed through the lens at level. When viewed perpendicularly to the lens, the width and height of the oval is seen as a perfect circle. You can verrify that by measuring the projected lines from the oval to the side of the chart. The curvature of the lens is not really relevant in this situation, except for fish-eye lenses. Measure less and photograph more. That's the way to get the best of any lens. Get intimate with your lens (lenses) and learn it's capability. It takes months to get use to just one lens.
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Last edited by ebooks4pentax; 04-13-2010 at 11:10 PM.
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