Charles, I get your explaination, but I look at the distances and light paths involved and can't imagine much of an angle at f2.8. The opening is a lot bigger, but that dirt has to be right on top of the sensor...and the light gets around it ?!! Regards, Bob S.
On Tue, Jun 15, 2010 at 3:15 PM, Charles Robinson <[email protected]> wrote: > On Jun 15, 2010, at 15:07, Chris Mitchell wrote: > >> Bob Sullivan wrote: >>> I still don't understand how is is there at f22 but gone at f2.8, >> >> I've always rationalised it as small aperture = large depth of field. Spots >> come nearly into focus at f11 and smaller. At 2.8 they're so out of focus >> they don't register. Is this right anyone? >> > > At a wide aperture, light rays that pass through the dust spot are coming > from ALL OVER the lens from millions of different angles (left, right, top, > bottom, etc) and there are a million little dark spots which are spread out > amongst all of the other light which is hitting the sensor. The lack of > light from that one little spot is not noticable. > > At a narrow aperture (let's get down to an impossible aperture that is one > photon wide for the example), you get down ultimately just a few rays of > light heading through the aperture, through the dust spot on their way to the > sensor. If they are blocked, there IS no other light from other angles to > hit the sensor and you end up with a dark spot. > > It's kind of like the depth-of-field explanation except that the spots are > never really in or out of focus. > > This isn't a perfect explanation. if I could draw it on a piece of paper it > would be perfectly understandable. > > -Charles > > -- > Charles Robinson - [email protected] > Minneapolis, MN > http://charles.robinsontwins.org > http://www.facebook.com/charles.robinson > > > -- > 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.
