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.
The visibility of dust has *nothing* to do with Depth of Field or any of that malarkey.
"Dust on the sensor" is analogous to a little ball held half an inch from the wall. If you light the ball with a broad light source (large lens opening), its shadow on the wall is very soft and difficult to see. If you light the ball with a point light source (small lens opening), the shadow is very well defined.
Why? Just imagine ray tracing light from a point source compared to a broad source. It should be obvious to you.
Godfrey
