On Mon, Jun 26, 2006 at 07:53:02PM +0200, Martin Trautmann wrote: > On 2006-06-26 12:40, John Francis wrote: > > You're both wrong. It's either no darker (just cropped to a > > smaller area) - > > so you assume that there's no additional magnification within the > viewfinder? Personally, I assumed first that the viewfinder image is the > same as before. I checked - and I'm wrong. > > Analog kameras where at abount 0.7 .. 0.8 magnification, covering around > 92 % (MX/ZX series). *ist was 0.7 of 90 %. > > Digital cameras where 0.95 of 95% (*istD or *istDS) and 0.85 of 95% > (*istDL and probably K100D). > > I guess this is somewhere in between: the viewfinder is not half area (as the > sensor is, cropped from 24x36 to roughly 18x24). But it's not magnified to > full format viewfinder either. > > > so just as bright in illumination per equal > > area (or equal solid angle submitted at the eye), or it's > > 1/(1.5)^2 as much total illumination, which is a little over > > one stop difference (it's like going from f/1.4 to f/2.1). > > Hm - I guess you are right. Half sensor area translates directly to half > light, which is exactly one aperture step. > > So what's the total? (1/2 * 0.95) / (1 * 0.7) = 0.67. The K100D has 67% > brightness of a ZK-L? Please correct me when I'm wrong...
Totally bogus. You either don't need the magnification at all, if you are measuring the total amount of light energy the viewfinder, or you need the square of the magnification as a measure of area. In any case, you're making it far too complicated. Ignore the coverage - what you really care about is how bright a unit area of the viewfinder looks. The K100D has, we will assume, 0.85x viewfinder magnification. A ZX-L has 0.7x. That means the image in the K100D viewfinder appears (0.7/0.85)^2 (which, by a coincidence, is pretty close to 67%) as bright as in the viewfinder of the ZX-L - a difference of just about half a stop. If you also take into account the difference in total image size (the DL shows .95^2 of a 24 x 16 sensor, while the ZX-L shows .90^2 of 36 x 24) you get another factor of two in favour of the ZX-L. But showing twice as much illuminated area in the viewfinder doesn't make a given part of the image any brighter - it would only be important if you were using the viewfinder as a light source to illuminate something else. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
