Thanks Yvon! Having the chart standing at 45 degrees is a great idea...but now I have no excuse not to test all my lenses to see how they behave (even though I don't own the K20D) :-)
Chances are that all your lenses are okay. If not, you can always shoot at a smaller aperture, expanding the depth of field anyway. It's jun fun to know how they are calibrated.
As a K20D owner, many thanks for the efforts! I have a question regarding the center part of the chart. I have used another AF test chart design and it involves laying the scale part of the chart 45 degrees from the flat surface but its focus target part is cut and twisted so that it is vertical (90 degrees to the flat surface). I think this makes sense because Pentax's current AF sensors are quite large and are larger than the markings in the viewfinder. If the target area is not vertical, it may cause the large-area sensor to focus to the lower side of your target and cause problems. Sorry English is not my native language but I hope you get my point. Just a thought. Thanks again.
Yes, that's an idea. The file is an AutoCAD file .dwg. If anyone would like the AutoCAD file, just email me and I'll send it to you as long as you promise to share your results with all of us.
The way the chart was designed, it stands at 45 degree on a flat table. Notice that the center portion is oval in shape but when viewed from a camera placed horizontally, the oval becomes a circle and the dimensions become accurate. The face of the chart is actually the long side of a 90 degree triancle (hypotenuse) and the chart accounts for that. When viewed perpendicularly, the dimensions and circle are elongated but when viewed at 45 degree, the circle can be seen and the dimensuins match. It has nothing to do woth the full sensor. The sensor center AF point is the only AF used for this chart.
The centre "target" is way too small with too many extraneous elements for the centre AF to lock on to. NB the AF sensor is much larger than the red dot in the VF. Secondly the term "depth of focus" is incorrect. It should be Depth of field (depth of focus is defined at the sensor side). You may be interested to know that the service manual for the GX10 specifies an FA50 at 1m distance with a flat B/W target on a tripod (and a ruler below it). White part lit at EV12.
8 comments:
Thanks Yvon! Having the chart standing at 45 degrees is a great idea...but now I have no excuse not to test all my lenses to see how they behave (even though I don't own the K20D) :-)
miserere,
Chances are that all your lenses are okay. If not, you can always shoot at a smaller aperture, expanding the depth of field anyway. It's jun fun to know how they are calibrated.
Perhaps you could make the dwg file available too, so we can enlarge it losslessly?
Hi Yvon,
As a K20D owner, many thanks for the efforts! I have a question regarding the center part of the chart. I have used another AF test chart design and it involves laying the scale part of the chart 45 degrees from the flat surface but its focus target part is cut and twisted so that it is vertical (90 degrees to the flat surface). I think this makes sense because Pentax's current AF sensors are quite large and are larger than the markings in the viewfinder. If the target area is not vertical, it may cause the large-area sensor to focus to the lower side of your target and cause problems. Sorry English is not my native language but I hope you get my point. Just a thought. Thanks again.
Peter
To anonymous,
Yes, that's an idea. The file is an AutoCAD file .dwg. If anyone would like the AutoCAD file, just email me and I'll send it to you as long as you promise to share your results with all of us.
To Peter Fang,
The way the chart was designed, it stands at 45 degree on a flat table. Notice that the center portion is oval in shape but when viewed from a camera placed horizontally, the oval becomes a circle and the dimensions become accurate. The face of the chart is actually the long side of a 90 degree triancle (hypotenuse) and the chart accounts for that. When viewed perpendicularly, the dimensions and circle are elongated but when viewed at 45 degree, the circle can be seen and the dimensuins match. It has nothing to do woth the full sensor. The sensor center AF point is the only AF used for this chart.
The centre "target" is way too small with too many extraneous elements for the centre AF to lock on to. NB the AF sensor is much larger than the red dot in the VF. Secondly the term "depth of focus" is incorrect. It should be Depth of field (depth of focus is defined at the sensor side). You may be interested to know that the service manual for the GX10 specifies an FA50 at 1m distance with a flat B/W target on a tripod (and a ruler below it). White part lit at EV12.
Yes the actual size of the center AF sensor is much larger. Take a look at this post on DPReview.com:
http://forums.dpreview.com/forums/read.asp?forum=1036&message=27982148
I am borrowing from the above post an illustration of the center sensor:
http://www.pbase.com/ivanglisin/image/94038933.jpg
This is very much in line with what PopPhoto published when they tested the *ist D which uses the same SAFOX VIII AF sensor hardware.
Peter
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