Camera lenses have different focal lengths that determine their usage and the type of subjects they are suited for. Standard lenses around 50mm are general purpose lenses, wide angle lenses between 10-40mm can capture wide panoramas and interiors, and telephoto lenses over 70mm are used for portraits and sports from a distance. Other specialty lenses include fisheye, macro, tilt-shift, and zoom lenses.

1. Understanding
Camera Lenses

2. The Focal Length

3. The Lens Ratio
which is the maximum aperture of the lens.

4. Standard/Normal Lens (50mm)

5. Wide Angle Lens (10-40)

6. Telephoto Lens (70mm ->)

7. Zoom Lens

8. Fisheye Lens

9. Macro Lens

10. Tilt-Shift Lens

11. Focal Length Lens Type Common Subjects
8mm - 24mm Ultra wide angle (fisheye) Wide panoramas and skyscapes, artistic
24mm - 35mm Wide angle Interiors, architecture, landscapes
35mm - 85mm (50mm common) Standard General purpose
85mm - 135mm Short telephoto Portraits, candid
135mm - 300mm Medium telephoto Close sports, action
300mm+ Super telephoto
Far sports, wildlife, nature, astronomy

12. CROP FACTOR

14. F STOP

15. F STOP

16. LENS CHARACTERISTICS

17. Lens Distortion

18. Lens Distortion

24. Lens Diffraction
light begins to disperse or "diffract" when passing through a small opening (such as your camera's aperture)

27. Bokeh
the quality of out-of-focus or “blurry” parts of the image rendered by a camera lens
A good bokeh pleases our eyes and our perception of the image and therefore, the background blur should appear soft and
“creamy”, with smooth round circles of light and no hard edges.
The shape of the reflected light in out of focus areas depends on the lens diaphragm