Again ... Shadows from a broad light source vs a point light source. That's the answer.
Godfrey
On Mar 9, 2005, at 3:23 PM, Juan Buhler wrote:
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
