More technical stuff: Camera lenses.

Crash course on lenses.

After collecting all the information, this is a short example of lens abbreviations:

50mm - the focal length.  50mm is the average length - the field of vision the naked eye can see. If you see a single number describing a lens, it is a fixed lens and cannot zoom to other focal lengths.  (Meaning you have to physically move closer or farther to fit in groups of people or to get closer to a far-away boat in the ocean).

f/1.8 - the focal ratio.  A ratio of the focal length and the aperture.  The smaller this number, the better.

IS - Canon's abbreviation for anti-shake.

USM - Canon's abbreviation for a quiet, fast zoom.


 My notes:

50mm lenses are the standard for all photographs.  It's the closest match to what the naked eye sees.

Below 50mm is wide-angle...

28mm is common for wide-angle (groups of people, landscapes).

Anything below 20mm is ultra-wide-angle.  A fish-eye lens falls into this category.

Larger than 50mm are telephoto lenses.  Good for close-up, details, and are more flattering for pics of people.  (note: blurs the background, which can be ideal for close shots)

85mm-135mm are good for portraits.

200mm and more is good for wildlife and sports.  Sports photographers typically use lenses over 600mm.

* You can buy zoom lenses where the focal length is adjustable.  The quality is not quite as good as a fixed focal length lens.
*Fixed focal lenses also take better pics in lower light.

Zoom lenses:

General purpose lenses usually go from 28mm-80mm.

Super zoom lenses: 28mm-300mm.

Wide angle zoom lenses: 16mm-35mm

Telephoto zoom lenses: 70mm-300mm



**** DSLR cameras have smaller sensors, so the focal length of any lens changes (multiplies by 1.6x for Canon).

So...

"This means if you want 50mm standard coverage on a Nikon cropped DSLR, you’ll actually need to use a lens with a 33mm focal length (35mm models are closest). If you want 28mm wide angle coverage, you’ll need to use a lens with an 18mm focal length, and so on. So always remember to multiply the actual lens focal length by the crop factor of your particular DSLR – that way, you’ll know what you’re getting."

Standard 50mm lenses on most DSLRs act like a short telephoto of 75mm to 100mm.

LENS APERTURE:

The bigger the lens aperture, the more light gets let in, so the better they work in dim environments.

The aperture in a DSLR camera is called the focal ratio or "f-number".  (This is the ratio between the focal length of the lens over the diameter of the opening in the lens.)  You can usually adjust the aperture (the iris opening), but the important figure is the largest aperture (smallest f-number). 

AUTO-FOCUS and ANTI-SHAKE:

All of Canon have auto-focus.  The "USM" (ultra-sonic motor) is quicker and quieter.

Shaking:
Sometimes while following a subject and taking pics in quick succession, an anti-wobble camera will mistake it for wobble and try to correct it.  Some cameras can correct only vertical wobble.  You can usually switch the anti-shaking off.

Canon calls this anti-shake "IS".