Photoshop shows values based on [EMAIL PROTECTED] 127 is the mid point, and it's about 25.5 points per EV step for the full range from Zone 1 to Zone 10. So 130 is right around Zone V and 80 is right around the boundary between Zone 3-4, so it looks like you are showing about 1.5-2 steps light falloff from center to edge wide open, a rough first order approximation.
(Lightroom shows it to be about 51% brightness on center and 32% at corners, again showing a little less than 2 steps falloff to the corners. 10% on grayscale value is 1 step in Lightroom's scale.) Godfrey On Nov 7, 2007, at 1:53 PM, Dario Bonazza wrote: > Hi folks, > > Here is a white-wall shot taken with the DA* 50-135 @ 135mm F2.8, > where it > shows its highest light falloff at corners: > www.dariobonazza.com/public/Vignetting.jpg > > Do yo have any idea about how to measure that? I mean, how to > translate > Photoshop values (around 130 for each RGB channel at center, around > 80 at > corners) into f/stops? > > Thanks to anybody enlightening me ;-) -- 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.
