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05-17-2008, 07:04 PM   #1
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AF adjustment test chart specifically designed for the Pentax DSLR cameras.

Hi Pentaxian and friends,

The Pentax k20d has a special function located in the Custom Setting menu. It is Custom Setting No. 34 and it is called Focus Adjustment. According to Pentax, all newer DA Series of lenses are tuned at the factory for proper focus with all Pentax DSLR bodies. However, the older K-mount lenses may produce back or front focused images. The K20D’s AF Adjustment function allows the adjustment of the focus position for these lenses and can store up to twenty lenses in its memory. It is also possible that newer DA lenses need adjustment as well. Any high precision instruments, such as modern lenses, may need calibration once in a while. With the K20D built-in firmware, you can check and adjust all your current Pentax K-mount lenses.

Reading the Pentax manual, or our book, the Pentax K20D “Everything you need to know…and then some” for that matter, the AF Focus adjustment function is explained, but there are no adjustment chart to comprehensibly adjust the focus of any lenses. A bench mark chart is required. There are a few AF focus check charts floating around on the internet, but I have not seen any designed specifically for the Pentax line of DSLRs and lenses. The charts I have seen on the internet were all designed with the Nikon products in mind, although there are no in-camera adjustments possible with these DSLRs. All you do is checking the back or front focus problems so that you can send your lens or lenses to the manufacturer for adjustment. On all the charts I have seen, either the English measurement scale or the Metric measurement scale were incorrect. I also noticed that they required laying the chart on a flat surface and position the camera at 45 degrees, which is a little difficult to do accurately.

Well, it took me a little while, but I designed a chart for the Pentax line of DSLRs and lenses. It is free for the download amd will also be included with all K20D books. It is very simple to use and will stand at exactly 45 degree on a flat surface, requiting you to simply set your camera horizontally. The chart was designed with AutoCAD. (This is an engineering design software package, for those of you that are not familiar with AutoCAD). The chart measurements are exact and adjusted on the 45 degree plane to reflect and measure the exact back or front focus depth. In other words, it shows the exact depth of focus measurements in millimeters or inches, from the 45 degree position. It just required a little trigonometry formula for right angle triangle.

The actual method of checking your lenses is written on the sides of the chart. You can download the chart here, Pentax K20D AF Adjustment Chart.

Here are the instructions for setting it up. You can use the chart as you please and distribute it to anyone, but you cannot sell the chart or reproduce it for publication without written permission. I think that’s fair enough.

1. After downloading the PDF chart, print it preferably on a thick stock letter sized paper. I used a matte photo paper with a 61lb weight / or 10 mil thickness.
2. Next, cut the chart where is says “Cut at line”. 3. Score the chart where is says “Score and fold”. Scoring simply means to use a straight edge and a dull side of a knife and tracing along the line to make an indentation in the paper so that folding becomes easier and precise. 4. Fold the chart as shown. 5. Staple of tape the chart pointed end as shown. The angle is already adjusted so that the chart will lay exactly at 45 degree when placed on a flat surface such as a table or desk.
Use the instructions on the chart to test your lenses.

The chart is small and will work just fine with lenses capable of focusing as close as 6" to 9". If your lens cannot focus as that small distance, then the chart is not big enough. If you have a way to enlarge it, do so. The measurements in mm and inches won't be accurate anymore but you will be able to tell if the focus is accurate. If you could enlarge the chart to 3 feet tall, it would be adequate for extreme telephoto as well.

You can read the chart directly on the camera monitor with the zoom function, but I found it easier to print it.

That’s all there is to it.

ADDITIONAL COMMENTS:
I hope you find the chart useful and please email me with your questions or suggestions. I realised quickly after I posted this thread that this a highly controversial subject as all the negative members did come out in force. To all these members, It would be nice if you could post some of your greatest pictures so that we can all see if you can indeed take great photos or are just pixel peepers and agitators. When criticizing the chart negatively, please let us know what accurate way you would check your lenses. It would help a lot. Help by coming up with solutions, if you don't agree with whatever is posted. Isn't what these forums are for? This is a site for Pentax owners and we are here to help each other. I love Pentax Forums because it is a great and friendly site for Pentax owners. So please , the RiceHigh and company, get of of your soapbox and help positively. The chart is clearly designed for the K20D owners as you can change the AF adjustment at will in the Custom Setting menu No. 34, and it is non destructive. You can reset it anytime you want. And don't change the setting just because...do so only if you consistently have front or back focusing problems.

Thank you for reading,

Check the blog for downloading the chart and instructions to use it.

Pentax DSLRs

Yvon Bourque


Last edited by ebooks4pentax; 05-31-2008 at 08:43 PM.
05-17-2008, 07:22 PM   #2
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you need to check your"perfect focus shot, as I believe it is actually front focused (although it is a little difficult to tell in the uploaded resized version.

the reason I asy this is that for perfect focus, the depth of field is 1/3 in front of the focus point and 2/3 behind the focus point.

Your perfect focus shot has more in front of the focus line clear than behind it.
05-17-2008, 08:00 PM   #3
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I agree Lowell. I think these charts we see online are quite dubious. This is the latest "45 degree" chart. I see Yvon has posted this on all the Pentax boards, but he usually doesn't reply after his initial posts. There is some argument that the 45 degree test is not accurate. I posted on another thread my experience with that test, and the results. The test caused me to make adjustments to the k20d that were not necessary. I wonder how many people have needlessly sent in cameras to be repaired because of this test.

Another thing that concerns me on this test is that there are alot of things for the AF to lock on to in the center. Even on "spot" focus mode, what is the guarantee that it will lock on the center?

Why wouldn't it be better for us to simply type some text on sheet of paper, and tape it too a wall, and focus on that? Adjustments could then be made accordingly. On a camera that doesn't have adjustments, then you know for sure to send it in.

Last edited by PentaxPoke; 05-17-2008 at 08:10 PM.
05-17-2008, 08:07 PM   #4
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I used the D70 focus chart last time and shocked to see that my Tamron 28-75 is out of focus. But in actual usage, I find the lens tack sharp. The only time I find the focus is out is when I am using f2.8 and trying to snap a shot in very dark areas and without flash.

05-17-2008, 08:31 PM   #5
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QuoteOriginally posted by PentaxPoke Quote
I agree Lowell. I think these charts we see online are quite dubious. This is the latest "45 degree" chart. I see Yvon has posted this on all the Pentax boards, but he usually doesn't reply after his initial posts. There is some argument that the 45 degree test is not accurate. I posted on another thread my experience with that test, and the results. The test caused me to make adjustments to the k20d that were not necessary. I wonder how many people have needlessly sent in cameras to be repaired because of this test.

Another thing that concerns me on this test is that there are alot of things for the AF to lock on to in the center. Even on "spot" focus mode, what is the guarantee that it will lock on the center?

Why wouldn't it be better for us to simply type some text on sheet of paper, and tape it too a wall, and focus on that? Adjustments could then be made accordingly. On a camera that doesn't have adjustments, then you know for sure to send it in.
Actually, as long as the center spot is in focus, everything is fine. I do say that on the instruction written on the sides of the chart. You have to check the focus with either the chart at 45 degree or tilt the camera at 45 degree, otherwise you cannot see the depth of the front or back focused area. The test is done at the maximum aperture of the lens and at the closest distance possible with the lens still capable of focusing. Actually once the closest point of AF is found, It would be better to back off a little. So this would constitute a worst scenario possible. How many times do you shoot at the maximum aperture and at the closest distance the lens can auto focus.

At the end of the day, it's not about what the chart says, it's about how your pictures look and the actual composition of the picture. There are no substitute to taking a real picture, but it's fun to test your lenses.

Don't take yourself too seriously, and just adjust your lens if you consistently have many pictures with front or back focus problems. You might be the problem, not the lens.


Best Regards to all,

Yvon Bourque

Last edited by ebooks4pentax; 05-18-2008 at 12:24 AM.
05-17-2008, 09:38 PM   #6
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I want my own personalized focus chart.

Instead of "K20D in focus" it would say "KungPOW you rock at manual focus!!"

"Backfocus" would say "Try again KungPOW, don't give up!"

I think the positive slogans would help me be a better photographer.

Then on the flip side there would be a chart to test the auto focus. "KungPOW's K10D is bang on!"

Ok enough of this. Too much sun today.
05-17-2008, 10:50 PM   #7
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I agree totally. This chart is even most useless!

Yes, this is the most dubious AF accuracy test chart I have ever seen. Not only it is just a clone to the original D70 "45 deg" focus test chart, the modified cross target simply will NOT let any crossed AF sensor to be able to focus properly - for any DSLR have its cross sensor aligned properly! (For anyone knows about the working principle of the DSLR AF systems will know why.)

It just looks like a big joke to me, from the technical point of view, sorry!

P.S. I'm afraid that if one wants to promote something, at least it must be technically sound. Don't mislead others with mis-concepts, please - just because if one just wishes to promote something!

QuoteOriginally posted by PentaxPoke Quote
I agree Lowell. I think these charts we see online are quite dubious. This is the latest "45 degree" chart. I see Yvon has posted this on all the Pentax boards, but he usually doesn't reply after his initial posts. There is some argument that the 45 degree test is not accurate. I posted on another thread my experience with that test, and the results. The test caused me to make adjustments to the k20d that were not necessary. I wonder how many people have needlessly sent in cameras to be repaired because of this test.

Another thing that concerns me on this test is that there are alot of things for the AF to lock on to in the center. Even on "spot" focus mode, what is the guarantee that it will lock on the center?

Why wouldn't it be better for us to simply type some text on sheet of paper, and tape it too a wall, and focus on that? Adjustments could then be made accordingly. On a camera that doesn't have adjustments, then you know for sure to send it in.
05-18-2008, 12:21 AM   #8
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QuoteOriginally posted by PentaxPoke Quote
Why wouldn't it be better for us to simply type some text on sheet of paper, and tape it too a wall, and focus on that? Adjustments could then be made accordingly. On a camera that doesn't have adjustments, then you know for sure to send it in.
Please explain this advanced technical method of checking the AF Adjustment. Emphasize on the "Adjustments could then be made accordingly".


Last edited by ebooks4pentax; 05-18-2008 at 12:29 AM.
05-18-2008, 06:35 AM   #9
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QuoteOriginally posted by k10dbook Quote
Please explain this advanced technical method of checking the AF Adjustment. Emphasize on the "Adjustments could then be made accordingly".
I have to say PentaxPoke's statement is true and accurate. From his comment, I dare to say he knows well on how AF systems of DSLRs work exactly and how testing/adjustment should be made.

He statement is clear and precise. What else do you want to elaborate/explain/emphasize?
05-18-2008, 06:57 AM   #10
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QuoteOriginally posted by k10dbook Quote
Please explain this advanced technical method of checking the AF Adjustment. Emphasize on the "Adjustments could then be made accordingly".
The best thing would be to have a single black spot in a field of white with the measures off to the side, the problem is that there is too much to lock onto with this chart.
05-18-2008, 07:14 AM   #11
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QuoteOriginally posted by Cideway Quote
The best thing would be to have a single black spot in a field of white with the measures off to the side,
Nope. The camera won't focus neither.

QuoteQuote:
the problem is that there is too much to lock onto with this chart.
Yes, I'm afraid. That's a good example on why quite often when people stole designs from others, reverse engineering (without the knowledge of original design and engineering) and re-manufacture something, those things just don't work or even if it works, it will have many new flaws.
05-18-2008, 09:50 AM   #12
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Do Not Use This Chart!!!

This chart is dangerous to use. Therefore, let me say it in bold letters for every reader of this thread.

Ignore this test chart!

It will give you wrong focus results!
(EDIT: This applies to both, the original and the revised version of the test chart, cf. below.)

The reasons have already been given:

QuoteOriginally posted by RiceHigh Quote
Not only it is just a clone to the original D70 "45 deg" focus test chart, the modified cross target simply will NOT let any crossed AF sensor to be able to focus properly
QuoteOriginally posted by Cideway Quote
the problem is that there is too much to lock onto with this chart.

The original D70 "45 deg" focus test chart has a single horizontal line surrounded by a large white area. For a reason...

Last edited by falconeye; 05-20-2008 at 06:46 AM. Reason: comment on revised version
05-18-2008, 12:14 PM   #13
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Agreed. This test chart has way too many things that may draw the AF sensor to focus on. I'd just use the d70 test chart if you're interested in this type of testing.
05-20-2008, 12:45 AM   #14
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Letís help each other become better photographers.

Hello Pentaxians and friends,

Before you read this reply, let me just tell you that pentaxforums is as good a Pentax forum as it gets. This is an exclusive Pentax site and lots of constructive information is shared here.

Yesterday I ishared an AF Adjustment Chart to help in determining if any particular lens has front or back focus problems. As I often do, I posted the major portion of the article on various Pentax forums. Several Pentaxians emailed me with some good suggestions as to how to improve the chart. I first tested the chart with a lens that focused as close as just a few inches and my chart worked well at eliminating the back focus problem I had. The lens was a Pentax SMC-F 35-70mm macro. Every time I would take a macro picture, it seemed that the actual photograph would be out of focus when, I was certain that I had focused properly. The K20D, with the AF Adjustment function was the right camera to test and adjust the lens.

I recognized yesterday that the target cross was too small for constant and accurate results. I changed the chart and incorporated a much larger center portion while retaining the overall design. Additionally, I scaled the center portion to almost the size of an 81/2” x 11” letter size paper. I still believe that it is easier to have the chart standing at 45 degree from horizontal while testing the lenses with the camera on a tripod and as horizontally leveled as possible.

If you look at the chart, the center is oval in shape when viewed perpendicularly. The reason for this is because when focusing on the chart with your camera leveled, you will notice that the oval shape turns into a circle, helping in visualizing when the camera/lens is leveled.

The oversized chart can be attached to the smaller chart with paper clips, to retain the 45 degree angle. It is at 45 deg because that way, the depth of field can be seen. If the sheet was flat, there wouldn’t be any depth to it. The Metric and English dimensions are accurate on the small chart, but the enlarged chart shown the dimensions also enlarged. Still, it does show if you have back or front focus errors.

Again, if other suggestions are emailed to me, I will first make sure that we all agree with the improvements and re-issue a once again improved chart.

Now, I assume that we all own and use Pentax equipment. My blog, the other Pentax blogs, as well as the dedicated Pentax forums should all have one thing in common. That is to help each other as Pentax users.

The reason I am bringing this up is that I experienced some rather condescending comments from some members of forums. Its one thing to share your knowledge with the entire Pentax audience, but it’s another thing to be rude and pompous toward other Pentax brothers and sisters. I won’t name any of the forums, as I am sure you already visit every Pentax sites on the internet. At the top of the list for rudeness, is a member from Hong Kong whose name you probably already know. That person should tone down a little from his self-proclaimed expertise.

A Pentax site should be embracing all Pentax users from the person with no experience that just bought a Pentax DSLR today to the most talented and experienced professional photographer in the world, whoever that is.

I wrote before that owning a Pentax DLSR was like being part of a big family. I truly believe that Pentaxians are a special loyal group. Let’s help each other become better photographers.

Thank you for reading, and thank you for all the constructive comments.
Download the AF ADJUSTMENT CHART HERE
Yvon Bourque

Last edited by ebooks4pentax; 05-31-2008 at 08:43 PM.
05-20-2008, 02:25 AM   #15
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Stupid question tome

before we get all wrapped up in a FF / BF issue., can any techno geek out there tell me exactly how big the AF sensor is with respect to the red dot in the middle of the finder, and how accutately it is placed.

Maybe our BF /FF issue is really more imaginary because the sensor is not exactly where we think it is. the 45 degree incline will amplify a vertical placement error and make it appear as BF / FF.

why not shoot the target vertically, and with AF turned off after that move the target in and out?
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