Aperture scale:

The brightest aperture is f/1. That 50mm lens costs about R100 000 or over $10 000. Where the focal length is 50mm,  the lens opening (aperture) at the back of the lens is also about 50mm, giving a ratio of 1:1 or 1/1 (actually f/0.98. When the aperture blades close down to let in half the amount of light, the opening is now 1/1.4. Halving again is 1/2. These increments are 1.4 (square root of two), with the odd steps being multiples of 2.

  • f/1         (base)
  • f/1.4      (1/1.4 of original area)
  • f/2          (1/2 …)
  • f/2.8    …
  • f/4        …
  • f/5.6     …
  • f/8         (1/8th)
  • f/11      …
  • f/16     (1/16th)
  • f/22    …
  • f/32     (1/32, only on a few lenses)
  • f/64     (on large format cameras)
  • f/128   (pinhole cameras use around f/137)

For f/16, the value of 1/16 means a small hole which lets in little light compared to the focal lenght or the original area (f/1 of that one lens, f/4 as a starting value of a lot of lenses).

Photo: www.michael.currin.co.za

For sport, I have a 75-300mm lens. At 300mm, the lens is only 20cm long rather than 30cm. This is partly due to front or backfocusing mechanics (the one is for telephotos, other for wide angles) and also the aperture, which happens to be f/5.6 and means the back element of the lens is small. Also the front of the lens is small, maybe 5cm.

But I have also rented a 300mm f/2.8 for a concer, which costs R60 000 new. It gave the same focal length as my other lens, but from f/5.6 to f/4 to f/2.8 it is 4x bright. But it is more like 50cm long and heavy. The opening at the back is large, the front of the lens is huge (probably 20cm).

Both lenses do stop down to f/22, as most lenses do. That is due to the aperture blades.