How Does it compare with the zoom of a compact digital camera having optical zoom of, say, 3X or 5X or 6X? This is 3rd grade math, once you know what to do. Just divide the little number into the big number and you get your "X" factor. There is a lot more to determining the "power" of a lens, though.
An 18-55 zoom is a 3X zoom. A 70-210 zoom is also a 3X zoom. How can this be? You know that a 200 mm lens wold give you a much larger image than a 55 mm lens, right? The thing is, with a point and shoot (non-SLR) camera, we tend to almost never pay attention to the focal length of the lens. It would be incredibly confusing if we tried to anyway! Image magnification is a direct function of the sensor size. There are many different sensors out there and without having some standard reference, comparing focal lengths would also become meaningless. This is why everyone still refers to the "35 mm equivalent."
Back to your question...
It seems like most point and shoot cameras with a zoom lens start out in the area of 28-or-35 mm. Let's just choose 35 mm for this example. If the camera has a 4X zoom, it would be a 35-140 equivalent. 140 mm is a moderate telephoto. Suppose it starts at 28 mm, though. This would be a 28-112 equivalent. 112 mm is also a moderate telephoto, but hardly impressive. It would seem that a 5X telephoto would be "better," but the 5X zoom starting at 28 mm would yield exactly the same 140 mm as the first example.
In other words... The "power" expressed in terms of [some number]X doesn't really mean that much. This is especially true in digital SLR's. What matters is the actual focal length of the lens. Fortunately - at least for sake of comparison - the majority of DSLR's have pretty much the same magnification factor and that is around 1.5 to 1.6. It makes direct comparisons a lot easier, but you have to develop a sense of what constitutes a "long" vs. a "moderate" telephoto.
Unless and until we have a major paradigm shift, it will still be helpful to think in terms of 35 mm equivalents when you are buying a lens. This is the "language" that we speak, using 35 mm as the de facto standard. Focal length comparisons make more sense that expressing the magnification by "zoom power."
Here's a chart that I'm making up just to get you started. It is in 35 mm equivalents. If you are putting a lens of this focal length on most DSLR's, you would have to do some math. Multiply the numbers I gave by .67 if the camera has a 1.5 "lens factor" or by .625 if it has a 1.6 factor. For example, in my list, I say that 50 mm is the "normal" lens for 35 mm cameras. If the DSLR has a factor of 1.5, this would mean that a 33.5 mm lens would be "normal" for that DSLR.
Ultra Wide - 10-20
Wide Angle - 24-35
Normal - 45-55 (50 mm is the accepted "normal")
Medium Tele - 85-135
Telephoto - 150-300
Super Tele - 400-600 if you go to cnet.com
digital cameras
they have a whole article on slr's If you look at various cameras at dpreview, you will see that along with the 3x or 5x or 10x optical zoom information, there will be a 35mm equivalency next to it. To calculate zoom, all you need to do is take the furthest point and the widest point. For example a 24-105 mm lens is 4.375X (105/24). And a 18-200mm lens is 11.1X (200/18).
Don't use magnification to compare. You can't compare that way because most point-n-shoots are around 36-105mm (3x zoom). You will rarely find a wide angle point-n-shoot. A 28-80mm lens is almost 3x and the reach is much shorter than the 36-105mm lens. If you really want to know, you should look at the mm instead of the magnification. If you get a 28mm lens, that means you have a wide angle lens such as a 10-20mm lens. If you want to zoom in, get the larger mm at the end such as a 70-300mm lens. The times part is just a marketing thing to make the camera look better. If you are really serious about a lens, check out the mm part. That's why they don't have the magnification on the lenses.
Look at the link below to compare the different focal lengths. Keep it simple. Divide the large focal length by the small focal length. So a 70-200mm lens is 200/70= 2.8X opctical zoom. divide tele with wide.. like if camera is 35mm wide and 105 mm tele..
then if you divide it will give you
3x |
