Shedding light on "theoretical texts" versus the reality of shooting images everyday.
So many texts advise us that when we want to capture an image with a long/large depth of field, typically found in landscape photography, we should be using the smallest aperture normally available to us, such as f22 - (remembering the larger the f-number, the smaller the actual aperture opening).
Unfortunately the "theory" doesn't take into account practical limitations of light transmission through a physical camera lens.
When the aperture is open, there is less diffraction of the light passing through, however when the aperture is reduced to a minimal size, then the light will diffract a greater amount. There is a whole scientific explanation around diffraction patterns, etc, etc. But what does this mean? Basically, at f22 the image will become "soft". It will lose some of its sharpness.
The answer - as a "rule of thumb", shoot landscapes from f9 through to f11. Characteristics of lenses will vary slightly with manufacturer and model, so worth experimenting a little, if you have the time.
There are a number of other factors and methods that can be used to gain the maximum depth of field, of which will be covered in future blogs.