Auxiliary/ Zoom lenses

Years back (not too many years really), 35 mm cameras came standard with a "normal" lens.  This was a 50 mm as a rule, described as normal as the angle of view of the 50 came closest to human vision.  Because the majority of digital cameras come with sensors smaller than the 36 X 24 mm size of the image on a 35 mm film frame, the word normal doesn't mean much any more when it comes to describing the lens.  The exception to this are the high-end, full-frame, cameras now made by Nikon, Canon, Sony, etc.  High-end also means high price as a rule as the cost of the large imaging chip (the size of a 35 mm frame) increases manufacturing costs a great deal.  Also many cameras that have interchangeable lenses are now sold with what is called a "kit" lens.  This is often a zoom in the 18 - 55 mm range.  While the kit lens produces acceptable images, it is not in the same league with pro lenses that are manufactured for those same cameras.

Lenses are manufactured with focal lengths that go all the way from "fish eye" with a 180° angle of view (often in the 8 to 12 mm range) to 1200 mm telephoto varieties which will cost you close to the price of a new car.  If you have a 1200 mm lens,  you'll probably also have to hire someone to carry it.  In addition to single focal length lenses, also called prime lenses, there are the zoom variety.  There was a time when the zoom lens was not considered to be in the same league as the prime, however that has changed and the quality is very high on all lenses currently being manufactured—especially those that are designed for pro level shooting.  Pro lenses for the Canon and others are not only built with special glass elements to reduce aberrations of various kinds and provide increased sharpness, they are built to withstand more punishment as well, with additional shock proofing, water proofing and dust proofing.  Canon pro lenses are easy to recognize as they have a red stripe around the barrel.

The image above of the hardware store plant sale was shot with a 7-14 mm zoom lens on a Panasonic GF1 camera.  The photo was taken at the short end (7 mm) but since the imaging chip is smaller than 35 mm there is a magnification factor (about double in this case) which means that at 7 mm it actually covers an area that is  the equivalent of 14 mm on a 35 mm frame.  The GF1 is a micro 4/3rds camera.  Even though the 7 converts to an approximate 14, it is still extremely wide and the linear distortion is apparent in the image.  As you can see, it is also a very sharp lens.

The previous posting of the dragonfly was shot with a 100 to 400 mm lens on a Canon 7D.  That camera has a slightly larger chip than the Panasonic and has a magnification factor of 1.6.  As it was taken at the 400 mm end of the range, the 35 mm equivalent would be 640 mm.  These equivalent numbers aren't particularly meaningful but it is worth remembering that cameras with chip sizes smaller than 35 mm will have a magnification factor and a telephoto lens will have a coverage area smaller than what would be normally found on that lens (meaning that it has a reach that is equivalent to a longer lens) and a wide-angle lens has a coverage area that is not quite as wide as what you would normally expect to have with that lens on a 35 mm camera.

It is also worth noting that with the wide-angle lens shot of the hardware store, the depth of field or area of sharp focus, is extreme and the picture is completely sharp, front to back.  On the other hand, the telephoto lens shot of the dragonfly has a depth of field that is so narrow, the insect itself is not completely in focus.