Do you get confused when you are at the camera store and the salesman starts talking about pixels, megapixels, sensors and resolution? Is the new "full-frame" sensor really the best? What does all this gibberish mean? It all starts with the camera sensor and pixel size.
I'm sure you have seen it - a compact point & shoot camera advertised as having more megapixels than a much larger Digital Single Lens Reflex (DSLR). So how do the companies cram more pixels into a smaller camera?
Sensor Size
Camera companies use different size sensors in their different models. It only makes sense a physically smaller compact point & shoot is going to have a smaller sensor size, physical length and width, than a large Digital Single Lens Reflex (DSLR), which generally uses the APS sensor sizes.
So back to my previous question - if the sensor size is physically smaller, why does it have more megapixels and resolution? They do it by making each pixel significantly smaller so they can squeeze more of them into the sensor.
O.K, so you ask, what does that have to do with anything? A lot! Compact point & shoot cameras are notorious for noise at the higher ISO and their images usually lack the tack-sharpness of a DSLR. While this may not be real evident at the smaller print sizes - say 8" X 10" or smaller - it becomes a huge issue at the larger print sizes. While you can remove some of the noise and do some sharpening with image-editing software, it usually isn't enough to make a big difference.
Pixel Size
Not all pixels are created equal. A larger pixel creates less noise and has a higher dynamic range, and because a large pixel takes in more light at the same aperture over a given amount of time, it creates a stronger light signal. In turn, this creates a higher signal-to-noise ratio making the image smoother and sharper. Dynamic range is the range of tones a pixel can produce between stark white and total black. The more tones created, the better color saturation and range of colors produced.
Full Frame verses APS
Some of the new DSLR cameras are coming out with full frame sensors, meaning their sensor size is the same as a 35 mm slide - 24mm X 36mm. While bigger is better as far as sensor sizes are concerned, there are a couple of things to think about before rushing out and buying one.
Being full-frame, if you have the auto-focus lenses from your old 35mm camera system of the same make, your older lenses will work just fine. The issue is how good are those older lenses? If you are using a cheaper lens with a full-frame camera, you can end up with vignette, soft focus and barrel distortion around the edges of your images taken at the smaller f-stops.
With a DSLR using an APS-size sensor, there is a built-in crop factor - Canon uses a 1.6 multiplier meaning your image is cropped from the center out and ends up magnified 1.6 times. Most lenses produce a clearer image in the center of the lens and it gets progressively "softer" as it moves toward the outside edges. Because of the cropping from the center to the outside, your "sweet spot" is saved and the softer outside portion is cropped out making for a sharper image.
Focal length
Using an APS-size sensor also changes the effective focal length of the lens you are using. Let's say you are using a 70-200mm zoom telephoto lens. With a multiplier of 1.6, your lens now has an effective focal length of 112-320mm. For sports and nature photographers, a longer effective focal length allows them to reach out and bring in a subject closer on a resulting image.
However, this same crop factor also works the same way on a wide-angle zoom lens. Your 17-85mm wide-angle lens now has an effective focal length of 27 - 135mm, which is not a good thing, if you need the shorter effective focal length. To get the shorter effective focal length, you have to get wide-angle lens with a shorter focal length than you need, so when the crop factor is factored in, it comes out at the effective focal length you want; an 11mm focal length will produce an effective focal length of 17mm.
So what does all this really mean? If you are looking at buying a new camera system - body and lenses - and you have deep pockets, then a full-frame might be the way to go, especially if you frequently make very large prints, such as in fine art work. However, if you already have a DSLR and a collection of lenses for it, then you may be better off just buying a new DSLR camera body with an APS-size sensor to take advantage of the new technology and features, but at a more moderate price and you can still use your present lenses.
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Ron
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