On May 1, 2007, at 6:32 AM, Cory Papenfuss wrote: >> Some folks have told me that replacing the focusing screen with a >> Pentax *ist DS focusing screen solved the problem. I might give that >> a try when I get a moment. I tried switching my custom Katz Eye >> screen from the DS into the K10D but found consistent underexposure >> with FA/DA lenses so that wasn't useful to me, but perhaps the Pentax >> DS screen will act differently. > > I've reported making it worse. Of course the split-prism adds a > whole other variable at small apertures. Perhaps the angle of > light going > throught the stock screen doesn't couple properly to light meter > sensors?
My Katz Eye screen is a plain matte fresnel surface without metering aids, a custom design for scribed lines. Yes, I talked with Rachel Katz about the problem I was seeing at length. Her take on it is that Pentax reshaped the scatter of the screen for the K10D model to provide more brightness at the ocular, which has the effect of reducing the amount of light at the metering sensors. So they use a different calibration curve for the sensors, based on the notion of less light going their way compared to the DS, to give accurate metering. I conjecture that there's an error in the calibration curve used when the camera is in the green-button stop-down metering mode. The progression of error as the aperture deviates from wide open is regular and it seems to me that the problem is an incorrect multiplier or lookup table. Godfrey -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
