6 A few examples of focal length (based on 35mm equivalents) include wide angle lenses, often around 24 or 28mm; telephoto lenses, anywhere between 80 and 300mm; and standard or all-purpose lenses, usually spanning around 28 to 80mm.For f-numbers, a camera you'll use for shooting indoors without a flash should have a lower f-number like 1.4 or 2, and a camera you'll use for shooting outdoors, especially of moving objects, should have a higher f-number, like 5.6 or 8, or even much higher like 16 or 22.