I've always seen on Digital consumer cameras the zoom factor (3x up to 12x). I assume that this means that at maximum zoom you will appear to be that many times closer to your subject.
I, however, have never seen this zoom factor mentioned with SLR lenses. For example there is acurrent thread on a Cannon 28-105 F3.5-4.5 II USM. This thread never mentions zoom factor. Why is this? Is there a way to calculate how much closer your images will appear? What is this calculation...
The "zoom factor" is not how much closer the subject will appear than it does to your eye, but it is the ratio of the magnification at the long end of the zoom to the magnification at the short end. It's also the ratio of the longest focal length to the shortest.
So, for a 28-105 lens, the "zoom factor" is 105/28 or 3.75x
The "zoom factor" is not how much closer the subject will appear than it does to your eye, but it is the ratio of the magnification at the long end of the zoom to the magnification at the short end. It's also the ratio of the longest focal length to the shortest.
So, for a 28-105 lens, the "zoom factor" is 105/28 or 3.75x
OK... Let's say then that I want to be able to pull far away objects closer, which focal length would I be using, the 28 end or the 105 end?
the zoom factor can be confusing, but easily understandible.
lets look at the Sony 717 camera as an example.
it has a lens that on the wide angle end is 38mm and on the telephoto end 190mm. to get the "X"factor you divide the telephoto end by the wide angle end and you get 5x zoom.
the "X" faxtor or zoom factor just means the range of zoom the camera has between the wide end and the telephoto end, not really how many more times you can bring an object closer to you.
on a D60 I use a 28mm to 200mm which equeals a 7x zoom, the difference between the sony and my camera with the 28-200 is 2 x, but that does not mean I get a full 2 x MORE powerfull, its close but not a full 2 x zoom.
Now lets take a look at my 80mm to 400mm zoom lens, that only comes out to a 5x zoom, but it has more reach than my 28-200, actually it has 2 times more reach. It just does not have as wide a range to select from for different focal lengths.
So basically what im saying is to not really pay attention to the zoom factor camera manufactures boast, but rather the telephoto lenght in mm the lense in or on the camera is OPTICALLY capable of.
