What is a lens?
Lens is the sets of round glass cut into a curved shape, neither concave or convex that exposes the light uniformly to the digital sensor. The glass or sets of glasses are call lens elements. Each glass has a particular job for the overall image quality by correcting or minimizing aberrations, flares and other optical imperfections like barrel distortions and vignetting.
|Left is a lens element without special coating and the right have a special coating to reduce lens flare.
Next is your aperture. They're work like your eyes iris with the use of blades. The larger the aperture the more light it allows into your camera by opening up those blades. The F number gets smaller when the aperture is fully opened, and the F number goes down when the aperture is near close. In most cases, you just need to know: the smaller the F number, the bigger the number on the price tag.
Examples of aperture fully opened and closed.
|Depth of field examples.
From normal lens, we can neither go wider (wide angle to fisheye lenses) or narrow (telephoto lenses). The interesting stuff that happens when playing around with focal length is the subject and the background/foreground start to interact with each other in the picture.
Framing the subject at the same spot on the photography with different focal length lenses.
Sources: Wikipedia.org; Canon EF Lens Work III
Please feel for to send me questions about you camera. I'm here to help.
This is Charlie Wang signing off. If you missed previous lessons, it's here:
What's a camera? and What's a sensor?