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02-23-2009, 11:22 AM   #16
Lowell Goudge's Avatar

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QuoteOriginally posted by newarts Quote
Thanks, Lowell, it is hard to argue with such nicely taken and presented data!

What's the physical explanation for it? IIRC the screen is not involved in metering; perhaps it is secondary reflections from the screen?

I believe that the screen is involved in metering directly, and I also note that even katz states spot metering is impacted by the split image. The following is a direct cut and pase from their site " Metering modes that weight the center portion of the scene heavily, such as partial metering, spot metering, and some manufacturers’ evaluative metering will be most affected."

From what I have read, and I can only speculate that there is a "scattering" of light off the focusing screen that causes off direct axis impact on the metering points. I believe this is related to the screen finish on the K10D and K20D, which is different than other pentax cameras.

As an analogy, I guess in a similar manner to the metering is impacted by the light entering the viewfinder, if you have the camera on a tripod.

02-23-2009, 11:34 AM   #17
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QuoteOriginally posted by warpedwoof Quote

...Here's the list: k17mm f4, k24mm f2.8, a28mm f2, m35mm f2, m50mm f1.2 & tak50m f1.4, m85mm f2, m100mm f2.8, smctak135mm f/2.5, m200mm f/4 and a300m f/4...
Wow! That is what I call a list.

I can second the value of a good focus screen. I installed a split-image with microprism a couple of months ago and have really enjoyed being able to do fine focus work again.


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