I frequently use K lenses (particularly the Vivitar I 90/2.5 and the Pentax 85/1.8), but I don't trust the meter. A test shot and a glance at the histogram is all that's necessary for accuracy. On May 10, 2008, at 12:28 AM, John Francis wrote: > > It's also got something to do with the angle of incidence of > the light on the metering screen. The K10D (and later cameras) > have a screen that's quite different from the one in the D bodies. > The K10D compensates for the non-linear response of the system, > but it assumes metering is being done wide open (I don't know > what it assumes for a pre-A lens, but I'd guess f/2.8 or f/4.0). > But if you're using stop-down metering at a small aperture the > K10D calculates the exposure incorrectly. > > I'm glad I decided, back when I got my PZ-1p in 1995, to stick > with a guideline of "A or later" for lens accquisitions. > > > On Fri, May 09, 2008 at 11:03:57PM -0500, Bob Sullivan wrote: >> Bill, >> >> I've found some exposure error as well with K and M series lenses and >> the green button. >> Somebody else mentioned it, and I don't understand it? >> >> I thought the green button closed the aperture down and measured >> light >> exposure values. >> I can't imagine how this is off, but here is an example with K35/2 >> lens. >> (The lens was set at different apertures and green button pressed >> before exposure.) >> >> http://picasaweb.google.com/rf.sullivan/K352ApertureTestOnK20d >> >> As you move away from wide open (f2) to smaller apertures (f12.8), >> light moves toward overexposure. >> (You can see more light in the big shadow on the right.) >> This did the same with an M400/5.6 although I didn't post the >> details. >> >> All I can figure is that it has something to do with the aperture >> lever being linear. >> Since the A lenses (and later), the movement has been linear. >> With the earlier M and K lenses, the movement is non-linear. >> Is it possible that the K20D measures the right exposure, and then >> sets a matching A lens aperture, >> not closing the lens all the way down to the f12.8 we have set? >> >> Regards, Bob S. >> >> >> >> On Fri, May 9, 2008 at 8:56 PM, William Robb <[EMAIL PROTECTED]> >> wrote: >>> One of the guys on the Pentax Dysfunctional Web Forum chalenged >>> me to test my K20 exposure >>> system with manual aperture lenses (green button manual). >>> The camera failed miserably, over exposing by quite a large >>> amount at all f-stops but maximum >>> and minimum. >>> Would it be possible for some others of us to run the following >>> test: >>> >>> Put a non A series lens onto their camera doesn't matter which, >>> but it would be nice to have >>> details, and run a series of exposures from maximum aperture to >>> minimum aperture to test the >>> linearity of the metering and perhaps report back. >>> >>> Sorry if this has been discussed before. >>> >>> I ran the test with several lenses, and then put an original >>> equipment istD screen into the K20 >>> as buddy thought that the screen itself was at fault, and >>> insisted that it had been a problem >>> with every DSLR since the istD. The screen was not the problem. >>> >>> Thanks >>> >>> >>> -- >>> PDML Pentax-Discuss Mail List >>> [email protected] >>> http://pdml.net/mailman/listinfo/pdml_pdml.net >>> to UNSUBSCRIBE from the PDML, please visit the link directly >>> above and follow the directions. >>> >> >> -- >> PDML Pentax-Discuss Mail List >> [email protected] >> http://pdml.net/mailman/listinfo/pdml_pdml.net >> to UNSUBSCRIBE from the PDML, please visit the link directly above >> and follow the directions. > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above > and follow the directions.
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