I haven't tried M or K lenses on the K-7 but did an experiment with the K-20 when new. Here are the results for a K35mm f2 at different apertures using the green button. (ie. select aperture, 'green button', take photo at selected speed)
http://picasaweb.google.com/rf.sullivan/K352ApertureTestOnK20d# The resulting exposures aren't bad, but seem best wide open. I can't figure out the mechanics of how it works. The exposures actually get lighter as you go to smaller apertures (bigger f #'s). I would expect the opposite. In practice, chimp if you use these lenses. Regards, Bob S. On Mon, Sep 13, 2010 at 2:02 PM, John Francis <[email protected]> wrote: > > I believe the issues surfaced when using lenses with a large maximum > aperture (such as a 50mm/f1.4). > > Although Pentax never explained exactly what was happening, the most > plausible hypothesis I saw was that the exposure metering in the K10D > (and, I would assume, in later cameras) had some sort of compensation > curve for the metering system based on the maximum aperture of the lens > (presumably because of known problems with light hitting sensors at an > oblique angle). An 'M' lens does not communicate maximum aperture (or > the aperture to be used) to the body, so the exposure correction would > not be performed (or would be performed using one fixed value for all > 'M' lenses at any aperture). > > I didn't pay too much attention to the issue, because I decided to go > with 'A' or later lenses back in '95 when I got my PZ-1p, so I rarely > put an 'M' lens on any of my later bodies. And, in any case, I don't > assume the metering on any DSLR is going to give me as good control of > the exposure as I can get by looking at the histogram. > > The "green button" metering technique should get you close; just be > prepared to apply some exposure compensation if you want it spot-on. > That was necessary (at least with the *ist-D and K10D) anyway; from > what Paul Stenquist says the K-7 may do rather better in this regard. > > > On Mon, Sep 13, 2010 at 08:35:49PM +0200, Jens wrote: >> >> I may be using my M lenses too little. But I have never noticed any exposure >> problems - except for those caused by the well known "slow aperture >> syndrom", occuring when lenses are left unused for too long - or stored with >> open aperture blades (on a camera or otherwise). >> >> I use a Seikanon wide angle macro lens quite often - which works like an M >> lens. It's an absolutely brilliant lens - which I believe is made by a >> company related to the later so well known Seiko brand. No exposure >> problems, that I know of. Razor sharp. >> >> Regards >> Jens >> -- >> Treat others as you would like to be treated yourself. >> >> On Sep 13, 2010 19:02 "Steven Desjardins" <[email protected]> wrote: >> > I've never really used an M lens on a Pentax digital, but I'm thinking >> > about buying one. I know the green button trick, but how well does it >> > actually work? Metering OK and all that? >> > >> > -- >> > Steve Desjardins >> > >> > -- >> > 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.
