[转帖]Optical zoom is optimal for cameras

乏味 · 发表于 2006-8-29 22:33:00

Q. Most of the digital cameras I see in Target and Best Buy ads boast 3X or 4X optical and digital zooms. Is there a difference between optical and digital zooms? And how does 3X and 4X compare to the millimeter zoom measurements on conventional 35mm film cameras?

-- J. Lutz of Belleville.

A. Although even my camera-clicking colleagues here had some trouble explaining this to me, let's see if I can bring it into focus for you with this general statement: There is a huge difference between optical and digital zooms -- and it's the optical that you'll want to zoom in on when buying. Here's why:

A camera lens works like your eye -- it collects light rays and brings them into focus on a "retina." In an old-fashioned camera, this retina is a piece of film; in a digital camera, it's an electronic sensor. In either case, the distance between the lens and where the light rays come into focus is the focal length of the lens.

Unlike your eye, a zoom lens allows you to vary that focal length, making images appear closer or farther away even while standing in the same spot. In a film camera, this is done by adjusting the moveable glass elements inside the lens, thus increasing or decreasing the field of view, but still keeping the image sharp.

Well, the optical zoom on a digital camera works much the same way. This might explain it best: If you have, say, a 2-megapixel camera, your picture will consist of 2 million pixels no matter how far in or out you go with your optical zoom. (A pixel -- short for picture element -- is a single, tiny point in an image.) You don't degrade the resolution of the picture by using the optical zoom, so your photo remains sharp.

Digital zoom is a different story. Once you reach the limit of your optical zoom, your camera's brain has to start playing around with those individual pixels to magnify the image more. And, once you start doing that, your picture quality starts going downhill.

Your digital "zoom" works by taking a certain area of your picture and blowing up the size of the pixels. So, for example, instead of using 2 million pixels to produce a 3x5 photograph, you are now taking an area of that photo with maybe 1 million or 1.5 million pixels and blowing them up to fill the same space. I won't get into the algorithms the camera uses to do this, but it boils down to this: The more you zoom in digitally, the fewer the pixels, the bigger they are and, generally, the poorer the photo.

Here's another way to look at it: Using the camera's digital zoom is no different than cropping and resizing the photo with a computer program later. In both cases, you lose resolution by cutting some pixels and blowing up the remainder.

Hopefully by now you understand why your optical number is far more important. Comparing it to a conventional film camera is a bit tricky, but here's a rule of thumb: Find out the camera's widest angle (smallest lens mm value) and mutliply it by its optical zoom X-factor.

For example, if the shortest focal length of the camera is about 35mm (as many are), a 3X would give you a maximum telephoto of about 105mm while a 10X would give you a 350. You, of course, have to decide what you need and what you can afford.

One final word of advice: Make sure you find individual optical and digital X-factors. Although I haven't seen it much lately, some companies apparently may boast a "20X zoom" without telling you whether it has a 2X optical and 10X digital zoom or a 4X optical and 5X digital, your better choice.

Q. How do you get yellowish keys on an organ white again? I bought a wonderful organ in good condition at an auction but I need help cleaning the keys.

-- K.R. of Evansville

A. To borrow an old toothpaste slogan, I wish it were as simple as saying, "You'll wonder where the yellow went if you brush your keys with Pepsodent."

Unfortunately it's not, and the keyboard shops, repairmen and restorers that I talked to all hit the same sour note: It's probably not possible.

Your instrument was manufactured in the '70s, so the keys are almost certainly a plastic or otherwise synthetic material, not ivory. You might try using a cloth dampened with lemon juice or bleach (wear gloves) on a small area and see what happens; just make sure you don't spill liquid on any electronic contacts.

Other than that, your only alternative would be to dress up your old organ in a new set of keys, something that would cost roughly $200, according to Morelock's Organ Parts in Rienzi, Mass.

Q. Is there anything I can do for squeaky windshield wipers? Cleaning them makes them worse, and I don't want to scratch the glass.

-- Andy Petraglia of Cahokia

A. You didn't tell me their age, but squeaking is usually a sign that your wipers are simply wiped out -- in every sense of the phrase.

According to the friendly folks at Plaza Auto Parts in Belleville, wipers may last two to three years if the car is parked in the shade all day and garaged at night. But if the sun beats down on them relentlessly as it has on mine the past month or two, your wipers could go in as little as six months to a year.

New wipers are soft and flexible so they act as a squeegee as they move silently back and forth across your windshield. Exposed to the sun, they become brittle and inflexible, causing that squeaky rattle. New refills would cure this.

The only other suspect is a windshield covered with excess roadfilm; try cleaning it thoroughly and see if it helps. And, of course, make sure the blades are installed properly.

FROM:http://www.belleville.com/mld/belleville/living/15367718.htm


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[转帖]Optical zoom is optimal for cameras

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