Zoom, Magnification, etc.

Zoom, magnification, and other such things.
1. For another zoom lens, ratio of maximum focal length to the minimum focal length is the zoom. for a Zuiko digital (ZD) 14 to 45 mm lens, this is 45/14, or slightly more than 3.

2. Optical zoom is the only 'true' zoom. When PS (point and shoot cameras) are advertised with 4X optical zoom and 3X digital zoom, the digital zoom part of it is simply equivalent to blowing up a photocopy on a Xerox machine. This does not help anything at all, and in fact fools people into believing that their camera has greater 'reach' than it really does.

3. If you want to better see (and photograph) a distant object, what you need is a lens with a large focal length. So what is a ‘large’ focal length?

4. For a Canon/Nikon DSLR, which uses an 23 mm (approx) APS sensor, I would say that between 150-200 mm enters the range of low telephoto. This is the lens you would use if you wanted to take face shots of people across the street.

5. A note on sensors: the film ‘sensor’ is 35 mm across. The APS sensor is about 23 mm across. This leads to the APS sensor behaving as if a 100 mm focal length lens is actually 150 mm. In other words, you multiply all focal lengths by 1.5 times when you use them on an APS sensor camera (such as Rebel TXi or a Nikon D80). The Olympus/Panasonic/Leica Fourth Thirds sensor is 18 mm across. Hence, the multiplier becomes 2 times.

6. So what is the big deal with a 10X zoom anyway?
If you were taking a picture of a building, you would want as much of the building in your viewfinder as possible. This means you would use a SMALL focal length, say 20 mm. Now, imagine that you were shooting pictures of a hot dog stand across the street. You would want nothing else, apart from the stand and the hot dog man in your viewfinder. To have a ‘tight’ frame, you would use a LONG focal length, say 140 mm. So if you had a lens that allowed you to change from a focal length of 18 mm to 180 mm, that would be perfect. In fact, such a typical lens, which has a zoom of 10X (see point 1) is offered by Olympus as part of their ZD line.

7. There must be a catch with these 10X lenses!
Yes, there is. Firstly, they are expensive. There are more optical elements to build and move. Then, these lenses will compromise on how large the aperture is at either end of their focal length range.

8. What is this aperture thing anyway?
It is simply the diameter of the circular opening through which light passes and falls on the sensor. This is expressed in terms of a ratio of focal length by aperture. Thus f16 means that the focal length is 16 times the diameter of the opening. A small ‘f-number’ means a large opening. This allows you to photograph fast motion, such as a speeding car, without blurring. Large apertures are expensive. A 10X lens will probably compromise on aperture.