I get this article from a photography magazine that i bought few months ago. The magazine is Popular Photography December 2008 edition. I found this article very interesting, so i want to share with you all. The article is about your most burning photography queries and the Popular Photography answer them once and for all.
1. Sensor size or number of megapixels - which matters more?
Neither. The most important variable is the size of the individual pixels. A pixel is like a light sponge - the bigger it is, the more light it absorbs. Greater sensitivity let's you shoot at higher ISOs with less noise, better detail, and finer color gradation. Of course, bigger pixels require a bigger sensor to hold the same number.
2. So that's the reason you get better pictures from a DSLR than a compact that has the same number of megapixels?
That's just one reason. DSLRs also tend to do better at image processing. They give you more control and, of course, a range of lenses. Other pluses: speedier startup time, lack of shutter lag, faster and more sensitive autofocus, clear and accurate viewfinder, faster burst rates, more powerful flash, many accessories, longer battery life, and typically greater ruggedness.
3. What's bertter, digital or optical image stabilization?
Digital stabilization is basically bogus - it simply boosts the ISO and shutter speed, and sometimes uses software to sharpen blurry areas of the image. Optical image stabilization is the real deal: Either the imaging sensor or an element in the lens moves to counteract your motion when handholding at slower shutter speeds.
4. What's the difference between Automatic and Program mode?
Automatic is pure point-and-shoot - the camera sets aperture, shutter speed, ISO, white balance, autofocusing mode, flash. We much prefer Program, which sets the aperture and shutter, but leaves the rest up to you. You can set some or all of other parameters, apply exposure compensation, and decide when you want flash.
5. What does Program Shift do?
It let's you change the aperture/shutter speed combination while maintaining the exposure. Say that in Program mode your camera chooses 1/250 second at f/8, but you're shooting a portrait and want to use a large aperture to blur out the background. With Program Shift, you set the aperture to f/2.8, and the shutter speed will automatically change to 1/2000 second, which gets the same amount of light to the sensor or film.
6. What's with "equivalent" focal lengths? Why do you sometimes call a 50mm lens a 75mm equvalent?
It refers to the corresponding focal length on a traditional 35mm film camera or full-frame DSLR. Because most DSLR sensors are much smaller than a 35mm frame of film, they record only the center of the image circle cast by the full-frame 50mm lens, producing images with the same field of view as those a 75mm lens would capture on a 35mm or full-frame SLR. (The difference in area is called the crop or lens factor.)
7. What makes one lens "faster" than another?
A fast (or bright) lens admits lots of light through a big maximum aperture. This allows you to use a faster shutter speed than you can with a small-aperture (slow or dim) lens. The f-number designation on a lens tells you the biggest aperture you can set, with lower numbers signifying wider apertures: An f/1.4 lens is very fast, f/2.8 is pretty fast, and f/5.6 is slow.
8. So is it better to use a full-frame lens on a DSLR that has a smaller sensor?
No. Since the smaller sensor records only the central "sweet spot" of the image circle, full-frame lenses theoretically should give you images that are sharper around the edges than digital-only lenses do - but there's scant evidence of that in the real world. Full-framers have some benefits: Retaining their utility if you upgrade to a full-frame DSLR with the same mount, for instance. But the crop factor means they can't give you an ultrawide angle of view - that 17mm lens becomes a 25mm equivalent on a camera with an APS-C-size sensor.
9. So, what does a range such as f/3.5-5.6 on a lens mean?
On less-expensive zooms, the lens get slower as you move to longer focal lengths. On an 18-55mm f/3.5-5.6 lens, for instance, you can set an aperture as big as f/3.5 at 18mm, but at 55mm the widest you can set is f/5.6. At an intermediate focal length - say 35mm - the maximum aperture will be around f/4.5.
10. Why should I buy a telephoto lens when I can just put a teleconverter on my kit zoom?
That will make your already-slow lens even slower. A 2x converter will make an f/3.5-5.6 lens, for example, effectively f/7-11, dim enough to prevent autofocus. And the teleconverters available for kit lenses tend to be of so-so optical quality. Better to put the money toward an inexpensive kit telezoom.