Originally posted by magnum1 I honestly can't as I am not knowledgeable enough. All I know is if I take two pictures, one at f2.8 and one at f11, spots will show up much more at f11. Have no idea why????
OK here's my attempt at an explanation -
Preamble -
First, I have noticed that dirt on film seems to show up sharper than dirt on digital sensors. On digital sensors they kind of look blurry.
I am speculating that dirt/dust on the sensor is on a plane other than the actual plane of detection/recording -
eg: the Bayer filters/lenses must have a finite thickness - which covers the actual pixel site.
Then there is the
optical anti-aliasing filter which again has a thickness -
Plus there may be some anti-static anti-dust coating(s) that may again have some thickness.
So between the two optical systems and any coatings - there is a finite amount of thickness/space that separates the dust from the actual pixel detecting site/plane -
so it's not quite like film which has the emulsion side facing the lens so any dirt/dust on it is on the actual capture/detecting plane.
Hopefully people are still following me?
There is
depth of focus (Wikipedia link) not to be confused with depth of field - this is the tolerance/depth that a projected image from the lens is actually in focus on the detection plane - eg: sensor or film.
The depth of focus is dependent on the aperture - so the smaller the aperture the greater the depth of focus - so with a smaller aperture the dirt will tend to be more in the focus part of the projected image - whereas with a larger aperture the dirt is more in the out of depth of focus part of the projected image.
This may explain your observation?
Anyone else care to comment, or correct this, please?