the amount of diffraction is determined by
lens size, and the amount of affect that diffraction has on part of your image, depends on how far that part of your image is from the
lens. so for an image with a film camera (not that sure with a Digital Camera), i work on s=D/1600d where s is the diffraction limited size of object, D is the distance from the
lens in feet, and d is the
lens size (focal length/f
stop). so if i am photographing the on the Sturt Reserve in Murray Bridge with a 35mm
lens at f11, and the twin bridges are 1km in the background, i know that anything that is just over a half a foot in size or larger will be rendered sharply in my image. So as you can see, by using a larger
aperture, we get better resolution and less diffraction, however our
dof is limited. But just over half a foot (16) allows me to render the basic structure of the bridge, but rivets and the shape of the beams are not detectable.
so beams of
light travel ina straight line, but when they are squeezed through a diagraphm opening, they divert. they still travel forward, but now at an angle, so obviously the further away an object is from the
lens, the more that diffraction will affect said object. now with a Digital Camera, you can just chimp, but if you ever graduate to a larger format camera, you may not have that luxury. the above calculation doesn't have to be worked out every time, you will become familiar with these figures. i know that for max
dof for most of my scenic shots, that f9.5 on my 35mm will give me great results.
as for
lens size, Ansel Adams named his school "f64". this was an f
stop that he often used. the
lens that he was quite partial to was a 300mm
lens, and he used this for alot of his work.
Lens size = 4.6mm