In order to get my mind off the ridiculous negotiations going on with a seller (they think it’s 2005 I swear), I did a little experiment to show how aperture value affects light.
Currently, I have 3 lenses for my Nikon D40 — the 35mm f/1.8, the 18-55mm f/3.5-5.6, and the 55-200mm f/4-5.6. What do all of these numbers mean? The 35mm f/1.8 means that the lens has a focal length (how “zoomed in” you are) of 35mm and a minimum aperture value (how large the opening in the lens in) of f/1.8. The 18-55mm f/3.5-5.6 means that it is a zoom lens, capable of zooming anywhere from 18mm (pretty wide angle) to 55mm. The aperture on this lens is variable, which means the minimum aperture value will change depending on the focal length I’m at — at 18mm I can use f/3.5, but as I go higher I must use a higher aperture value, with the minimum aperture value being f/5.6 at 55mm. This is a function of how the camera is built, and essentially makes the lens a little cheaper to build. You can buy zoom lenses with fixed apertures (usually at f/2.8), but they are usually much more expensive. Same thing goes for the 55-200mm lens, but at 55mm I can use a minimum aperture of f/4. On to the photos!
All of these photos were taken at 35mm, ISO 200, and 1/100 of a second. The only thing that changed between the photos was the aperture value, demonstrating what this photo would look like if I had taken each of my lenses and put it on their respective minimum aperture values.
This is a very simplified example, because there are a lot more factors that go into aperture value than light, but I hope it helps someone!