When to use f22 or higher

Started Jun 10, 2014 | Discussions thread
David Rosser
David Rosser Veteran Member • Posts: 3,468
Re: When to use f22 or higher

mactac wrote:

Clean the lens, when you stop down that far dirt on the lens is discernable.

The lens is clean. I'm talking about the sensor, and this thread is about stopping down

Quite and I fail to see how the dust on the sensor knows what aperture the lens is set at.  Perhaps you could explain the physics of why a "contact print" of a pattern of dust should be very clear when illuminated by a near point source and invisible when illuminated by a larger illumination source. (I accept I might have given you a clue here  ).  My comment is based on years of experience with film where similar problems occurred when using small apertures particularly on wide angle lenses where stopping down to really small apertures brings the front element of the lens into the depth of field.

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