While many lenses have a maximum aperture of f/22, some lenses have apertures that go to f/40 or higher!
Generally, photographers do not use any aperture above f/18 or f/22 because of diffraction. Diffraction is a phenomenon which causes a loss in sharpness because light rays are bent around the aperture.
The following is a story of when I broke all the rules and used f/40 anyway!
I was shooting a beautiful Christian cross on a ridge one morning. I knew the sun was about to rise just above the cross, so I wanted to take a picture of the cross silhouetted in front of the rising sun. If that's not symbolism, I don't know what is.
The trouble was that I had no neutral density filter, which would have allowed me to block out enough light. Shooting with a telephoto lens straight into the sun is a recipe for a disastrously over-exposed image. I guess I was feeling adventurous that morning, because I decided to use the aperture to block out the light. I had a little grin on my face when I cranked up the aperture right past f/22 and kept spinning and spinning. I was delighted to learn that the lens I was using could be shot at f/40!
I shot at f/40, a shutter speed of 1/4000th of a second, and ISO 100. In almost every case, this would produce a black picture, but I knew it was going to be really bright, so I gave it a shot. The image featured on this page is the shot that those settings produced. No, I didn't convert the photo to black and white. This is almost exactly as the shot appeared straight out of the camera.
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