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K-x focus screen drawing & Travor focus screen issue
Posted By: xjx, 06-08-2010, 01:27 PM

Forum member Luma discussed focusing issue of Travor focus screen on K-x (see: Travor focusing screen - BE AWARE!). The main part of the observation is that the object in the center of the split-image circle will not appear at the center of the captured image. Instead it is located above the center. When AF is used, the center AF point doesn't agree with the perceived point of focus in the split-image circle. As a result, AF will be off if one tries to focus to an angled surface (such as the 45 degree focus chart) using the center of the circle as focus target.

Being curious how this happens, I took out the stock focus screen of K-x and did some measurement. Here is a drawing I made based on the result:


From the drawing we can see the K-x focus screen has edges that appear clearer than the main part and will be covered by the metal clip when installed. The edge at the upper side is wider than the one at the bottom. The center focus point is located at the center of the grounded area (shaded in the picture) and thus should be a little bit below the center of the whole screen (offset by 0.5mm).

As a comparison, the Travor screen (which I also have) has the split-image circle exactly at the center of the whole screen. When installed on K-x, the circle will appear off center. One can see that by just looking into the view finder.

Last edited by xjx; 06-06-2012 at 10:12 PM.
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06-08-2010, 07:20 PM   #2
MSM
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Looks interesting. Thanks for the update.
06-06-2012, 10:13 PM   #3
xjx
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Don't know why the picture disappeared from the article. Just added it back.
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