THIS IS ALL MOOT, I HAVE FOUND WITH K AND M LENSES TO JUST ESTIMATE EXPOSURE BASED ON YEARS OF EXPERIENCE OR USE GREEN BUTTON
AND THEN TWEEK FSTOP OR SHUTTER SPEED SETTINGS BASED ON THE FIRST TEST EXPOSURE HISTOGRAM. THERE IS NO WAY YOU ARE GOING TO GET BETTER RESULTS THAN TWEEKING. ONLY ISSUE IS SPEED. BUT IF SPEED IS OF THE ESSENCE, YOU SHOULD BE USING KA OR KAF NOT K OR M. JCO -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Francis Sent: Saturday, May 10, 2008 12:28 AM To: Pentax-Discuss Mail List Subject: Re: K20 and manual aperture lenses 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. -- 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.
