Juan,
If I undertsand it... Warning this is my own mental meandering... It's not a matter of the lens focusing on the dust... obviously it can't as you say, because the dust is behind the lens as opposed to being in front of it.
Warning... still postulating...
It's a matter of the image that is hitting the sensor (generically used as opposed to the filter, etc., in front of the sensor). If that image is 'busy', with lots of detail and/or big tonality and/or color changes in a relatively small area of the sensor, it seems to obscure/hide/make less noticeable that there's dust present.
That's one of the things I believe...
Another item I just read, since I don't want to appear totally foolish is...
http://www.photo.net/equipment/digital/sensorcleaning/
And I think that answers your/my question.
Tom C.
his 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.
j
-- Juan Buhler http://www.jbuhler.com blog at http://www.jbuhler.com/blog
