By digital camera zoom I mean such things as 1x, 7x etc, by SLR zoom I mean 18-55mm etc... This site does a good job of explaining it.
Optical zoom is the number of times the maximum focal length of a zoom lens is larger than the minimum focal length.
Changing the focal length from 31mm to 50mm (50/31=1.6X optical zoom) reduces the field of view.
It's really all about math. 1x means it's the same magnification. 2x means double the magnification, etc. So 2x could go from 50-100mm, or 18-36.
Don't even bother with the digital zoom, by the way, just use optical. Digital zoom just crops your picture down in your camera and reduces the resolution.
http://www.dpreview.com/learn/?/key=digi... You'll really have to read the specs to find that out. 1x or 7x cannot be the only spec they provide. However, 1x means no optical zoom, 7x means the telezoom is equal to 7x wide angle, and all manufacturers provide the 35mm equivalent on their site (v.s. some sales site would ignore this importance information). You don't really need a website to do this conversion, as it is 3rd grade math. Just divide the little number into the big number and you get your "X" factor.
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 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
Footnote for photogeeks, as if anyone is going to read this...
The true "normal" is determined by matching the focal length to the diagonal of the negative. This would mean a "normal" lens for 35 mm would be 43 mm. I never understood why 50-55 mm lenses became the standard prime lens on these cameras. Do the math and you will see that a 6x6 cm camera would use an 85 mm lens as the prime lens and, in fact, that is what they ALL used. If a 35 mm negative was as tall as it is long, 50 mm would work out perfectly. Maybe I'll post a question and see who really knows... There may be something of use here. |
