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.