Thanks Godfrey. That's exactly what I was looking for. Dario ----- Original Message ----- From: "Godfrey DiGiorgi" <[EMAIL PROTECTED]> To: "Pentax-Discuss Mail List" <[email protected]> Sent: Wednesday, November 07, 2007 11:36 PM Subject: Re: How to estimate vignetting on digital images?
> 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. -- 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.
