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05-20-2008, 04:06 AM   #16
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Lowell, I have tried the D70 chart using both AF and Manual focusing. It gives about the same result.
I am told, because its doing it in AF as well as MF modes, its not a BF issue, but more than likely a mirror box problem of some sort, mirror out of alignment, or screen out of alignment.

The folks that have told me this are well versed in camera functions and cures, so i am tending to believe them.
My K10D is going back for round three to try and figure this out.

I have told Pentax Canada my theory and agree its possible.

Dave

05-20-2008, 05:38 AM   #17
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STILL Totally Useless and Very **MISLEADING**!

Despite I (and others as well) have already pointed out what's wrong with your reversed "engineered" chart, it's rather pity that you either haven't listened or still be unable to think about others' comments or yet don't understand, I will not explain further. (It doesn't matter anyway if you oneself understand or not, individually.)

What I want to tell ALL Pentax users here is that *latest* version of *your* chart will either:-

1. Fool the camera and make it unable to focus or hunt seriously for a properly aligned AF sensor against the centre;

2. Create FF or BF for a AF sensor which is shifted off the centre, although in real no such FF or BF will be seen.

If you really want to sell more of your books and promote your "gear books" (and as far as possible, for what I could see), I hope you should learn better knowledge yourself and don't create more unreal problems and mislead others as it shouldn't be.

No offense intended but these are just my humble opinions. I just feel upset and sad to see when such technically incorrect stuff and misconcepts are spreaded, especially by laymen who have little knowledge about the gear technics, but just mis-concepts (not even to say it can help anyone - only the reverse will be true).

NOTE: For those all others who really wish to adjust the AF using the K20D's built-in custom function or just wish to check BF / FF of our Pentax DSLRs other than the K20D, just tape a target on something which is vertically flat, e.g., a wall, and shoot to it directly (as PentaxPoke already pointed out in the beginning), don't use such a misleading "tool". Bottom Line: Simply use the original D70 test chart as a *rough* reference if one still wishes to shoot such "45 degree" chart, which is still usable and technically somehow correctly (just because the original inventor knew how an AF system of a SLR works).

QuoteOriginally posted by k10dbook Quote
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
05-20-2008, 10:18 AM   #18
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QuoteOriginally posted by RiceHigh Quote
Despite I (and others as well) have already pointed out what's wrong with your reversed "engineered" chart, it's rather pity that you either haven't listened or still be unable to think about others' comments or yet don't understand, I will not explain further. (It doesn't matter anyway if you oneself understand or not, individually.)

What I want to tell ALL Pentax users here is that *latest* version of *your* chart will either:-

1. Fool the camera and make it unable to focus or hunt seriously for a properly aligned AF sensor against the centre;

2. Create FF or BF for a AF sensor which is shifted off the centre, although in real no such FF or BF will be seen.

If you really want to sell more of your books and promote your "gear books" (and as far as possible, for what I could see), I hope you should learn better knowledge yourself and don't create more unreal problems and mislead others as it shouldn't be.

No offense intended but these are just my humble opinions. I just feel upset and sad to see when such technically incorrect stuff and misconcepts are spreaded, especially by laymen who have little knowledge about the gear technics, but just mis-concepts (not even to say it can help anyone - only the reverse will be true).

NOTE: For those all others who really wish to adjust the AF using the K20D's built-in custom function or just wish to check BF / FF of our Pentax DSLRs other than the K20D, just tape a target on something which is vertically flat, e.g., a wall, and shoot to it directly (as PentaxPoke already pointed out in the beginning), don't use such a misleading "tool". Bottom Line: Simply use the original D70 test chart as a *rough* reference if one still wishes to shoot such "45 degree" chart, which is still usable and technically somehow correctly (just because the original inventor knew how an AF system of a SLR works).
Rice High,

There again, you are just pointing finger at everyone on this site (not only this particular thread) with your self proclaimed expertise. Why don't you participate in a positive manner? Everybody knows that you always have negative threads about Pentax and that you favor Canon. You love picking arguments and I fell for this one.

If a moderator read this post, can you please delete the whole thing. This thread has turned out more like a DPR style of offensive discussion.
05-20-2008, 10:29 AM   #19
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The only thing more rare than an RH compliment of a Pentax product is an actual RH photo...

My comments were not to criticize the OP for his attempts to produce a focus chart. For that he should be applauded. My problem is the concept of a focus chart to begin with. I have had them fool me into thinking my camera was bad, only to find out that wasn't the case.

Thank you for your efforts Yvon, as well as your enthusiasm for our brand.

05-20-2008, 11:14 AM   #20
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Without doubt some chart testing may be useful especially when you are making adjustments and you want to know how far you still have to go. But there's a very simple test chart everyone can use just to find out about front or back focusing, and the good thing with it is it's not A4 or Letter size, so you don't have to be at macro range.
A spot on the pavement, oil or – whatever.
Shoot at full aperture, at an angle of 60-70 degrees, exactly which doesn't matter, center focus spot chosen and on the spot. You will see very quickly if the pavement is sharper in front of the spot (front focusing) or behind it. Since you are shooting from a high viewpoint, any focusing error will be amplified and well visible. You also eliminate the larger-than-expected sensor as a source of error, and most likely you have daylight and lots of it too.
Too bad I can't get that patented.
05-20-2008, 11:25 AM   #21
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I downloaded a copy of the Samsung GX10 service manual (the one presumably used by Pentax service technicians) and found a section detailing checking autofocus. The chart, instead of being at 45 deg, was set at 30 deg, with a half white/half black card on top of the chart. They manual shows the camera being focused at a point on the bottom of the white/black card just above the focus chart. The chart itself was set vertically, meaning the lines were running up/down rather than horizontally (across) the viewfinder image. And in the manual, it specified 30 deg. The chart was angled so the far end of the chart was on the left side of the image, the close end was towards the right. This goes against everything I've seen discussed where a focus chart is set at 45 deg, and the far end of the chart is at the top of the viewfinder, the close end at the bottom. They also specify that the focus point is not on the chart itself, but the dividing line between the white and black, at the bottom of the card nearest the focus chart.

I found this rather interesting, given the huge amount of talk given to BF/FF for the past couple of years. So, I guess my question is: which is correct, 45 or 30 deg, vertical or horizontal orientation of the chart?

I didn't bookmark the download site, but search on the pentax forum in dpreview for the topic on a russian program for turning on the debug menu in the K10D with pc software.

I don't know know if this would apply to the K10D and K20D, but I can't think of a reason why setting AF in the GX10 would be different.
05-20-2008, 11:29 AM   #22
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psh,

Any chance of you scanning and posting that focus chart from the manual so we could see it?
05-20-2008, 12:01 PM   #23
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I'll see what I can do. The manual is a pdf so I can copy the images, but I've never posted on PentaxForum. Soon as I learn how, I'll try it out.

05-20-2008, 12:21 PM   #24
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OK, I think I've got it. I screen captured the image of the chart/setup and the text from the manual. Wish they had an actual chart to print out, but such is not the case.




If the images don't show, here are the links:
af focus check text on Flickr - Photo Sharing!
GX10 Focus adjustment on Flickr - Photo Sharing!
05-20-2008, 01:38 PM   #25
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