Actually, I'm buying Godfrey's explanation more than this one. I think the difference between the angles of incidence should be negligible...
j On Thu, 10 Mar 2005 09:42:18 +1000, Rob Studdert <[EMAIL PROTECTED]> wrote: > On 9 Mar 2005 at 14:13, Juan Buhler wrote: > > > On Wed, 9 Mar 2005 15:14:32 EST, [EMAIL PROTECTED] <[EMAIL PROTECTED]> > > wrote: > > > > > Obviously a small (higher) f stop shows up fine detail that might get > > > blurred > > > with a shallower depth of field. > > > > > > This is precisely what is not obvious to me. If the dust is on the > > front element of the lens yes, it will be more visible at smaller > > apertures. But we are talking about sensor dust, which is right on the > > sensor, without a lens to "focus" it. > > Think of it this way and remember that the surface with the dust is suspended > over the active area of the sensor: > > At wide apertures the image forming rays pass through the lens over the entire > aperture opening and all focus at the film/sensor plane so the image forming > rays are coming from a wide range of angles so any object suspended above > obscures only a relatively small area of the image forming rays.. > > At narrow apertures the image forming rays pass though a narrow opening hence > that are conformed to pass though the dusty filter above the sensor surface at > limited angles hence anything in their path will be rendered as a more obvious > shadow on the image forming plane. > > Cheers, > > > Rob Studdert > HURSTVILLE AUSTRALIA > Tel +61-2-9554-4110 > UTC(GMT) +10 Hours > [EMAIL PROTECTED] > http://members.ozemail.com.au/~distudio/publications/ > Pentax user since 1986, PDMLer since 1998 > > -- Juan Buhler http://www.jbuhler.com blog at http://www.jbuhler.com/blog
