Digital Cameras: The Parts That Matter

Every digital camera has a body, lens, viewfinder, usually a colour LCD display, and controls. Other parts are explained in later pages, but here are the main ones that determine how good a camera is:

Lenses

The lenses on digital cameras vary greatly, and lens quality is a strong determinant of the quality of the images you can get.

Low end cameras have a fixed plastic lens, offering only one focal length (usually the equivalent of a 50 mm, or flat field of view).

Better cameras feature zoom lenses which go from moderately wide angle to telephoto. 3X or 4X is a standard magnification in digital telephotos, but some go up to 10 or even 12X optical zoom. Do not confuse optical zoom (a real magnification of the lens) with digital zoom, which merely enlarges pixels without good quality.

Better still are quality glass lenses, giving clearer optics than plastic.

Best are digital SLR’s, which have interchangeable lenses. Here you can buy exactly the lenses you need for different situations: a range of apertures and focal lengths, all with quality glass optics. The downsides are less convenience and more cost: a reasonably good telephoto lens begins at $500, more than the price of some DSLR camera bodies!

Fixed plastic lens	Zoom plastic lens	Fixed and zoom glass lenses for digital SLR

A wide range of lenses can be attached to a digital SLR body for different shooting situations.

You can see the mirror inside the body, which reflects the actual view through the lens into the viewfinder.

Aperture

Cheap digitals give you very little control over aperture, but slightly better ones let you set it. However, the range of F-stops is much less than an SLR, usually in the range of 3.0 to 8.0. This makes it hard to get really shallow or deep depth of field. The lack of wide aperture means you need slower shutter speed in low light than a bigger more open lens.

SLR’s give much better aperture control. A common strategy is to have one fixed lens (a 50 mm, giving a slight magnification) with really wide aperture, down to F-1.8, and one zoom lens going from wide angle to telephoto (18-200mm). Zoom lenses have smaller apertures than fixed lenses e.g. the lowest F-stop is 3.5 on the zoom lens pictured above versus 1.8 for the fixed lens. So if you’re shooting in low light you might choose the fixed lens with wider aperture.

Body

Small and sleek to large and bulky. Small is convenient and light, but harder to hold, less room for a good lens
Metal is stronger than plastic (but you really don’t want to drop any camera…)

Batteries

Good power essential for taking and viewing shots, and rapidly charging the flash
Running low on power in the middle of a shoot is annoying - always carry extras!
Power consumed more rapidly with use of flash, autofocus and LCD vs. viewfinder
Usually 2 to 4 AA’s or a special battery pack
Battery packs are often Lithium ion. This is a rechargeable system that will last for several hundred shots per charge
AA’s are convenient (you can buy or borrow regular ones anywhere in a pinch)
$50 spent on a charger and 4 rechargeable NiMH (nickel metal hydride) AA’s is a good investment. They should be good for easily 50 recharges, which could cost you $200 in normal alkaline batteries. When rechargeables are exhausted (won’t hold their charge), replacements are about $10 a pair. The mercury in normal batteries is a hazardous disposal problem, so using rechargeables helps the environment too.

Rechargeable NiMH AA’s	Rechargeable Lithium Ion Battery pack

Sensor Size: How Many MegaPixels?

You can see from the pics above that digital cameras advertise a certain number of mega pixels, ranging from about 3 to 12 and up these days. This means how many million pixels there are in the sensor. Since these sensors make up the picture, more pixels gives you a sharper, higher resolution picture. Are more megapixels always better? Yes, but it doesn’t mean the camera is better. You might get a sharper image with 4 megapixels and a good glass lens (like our Olympus) than at 5 megapixels with a mediocre lens.

You can calculate how big a print you can make from a certain size of image (how many megapixels), if you know the resolution of the printer. In this case, resolution means how many dots of ink print per inch. Each dot corresponds to a pixel on your CCD.

As an example, colour pages in our yearbook are printed at 300 DPI (dots per inch). So almost full page (8” x 10”) would take this many pixels:

8 x 300 x 10 x 300 = 7,200,000 pixels = 7.2 megapixels, double the capacity of some digital cameras.

It’s not that you can’t print an 8x10 from a 3.2 megapixel camera at 300 DPI. It’s just that it won’t be as sharp as it should be. If you blow up a picture too much, it will show pixellation, where you start to be able to see the square edges of pixels as a distracting pattern

Remember that a computer monitor only displays 72 pixels per inch (72 DPI), only a quarter of the resolution of a 300 DPI print, so what looks good on the monitor won’t look good if blown up to the same physical size on a high resoloution print.

Most cameras have an Image Quality setting that changes how many megapixels are captured depending what you need them for. For example, pics for web pages don’t need the resolution required for clear printing. Learning to set the quality/number of megapixels is a good idea – you won’t needlessly take up space of your memory card and computer.

Removable Memory Size: How many MegaBytes?

The sensor doesn’t store the image, unlike film which both captures and stores. The information from each pixel is sent to the camera’s internal memory, but this can only store 1 or a few pictures at most. Usually the pictures are automatically transferred to a tiny flash memory card. These can hold hundreds of images until they’re downloaded to a computer.

How many images can you store? It depends on:

The capacity of the memory card. Currently typical capacities are from 256 megabytes to several gigabytes (a gigabyte is a 1000 megabytes or a billion bytes)
The resolution of the pictures being stored. You might have an 8 megabyte camera (meaning the CCD has 8 million pixels), but choose to take pictures that only are 1 megapixel, because you don’t need such a high quality image.
The compression of the image. A 4 megapixel picture can be stored in less than 1 megabyte of memory, if it’s saved as a JPEG, because JPEGs are highly compressed. You lose a little quality in the compression, so professionals often choose to store in RAW mode, which simply records the colour of every pixel with no compression

So there’s no exact answer to the question, but shooting at the best quality on a 4 megapixel camera, you can store about 300 pictures as JPEG files on a 256 megabyte flash card.

LCD Monitor

The LCD screen is used to compose shots, review shots, and give information such as shooting mode, F-stop etc. This is distinct from the viewfinder, which is the smaller eyepiece at the top in the picture below.

Larger size is helpful in checking your images in the field. You can usually zoom in to see a bit of detail, but remember that images that look sharp on a 1.5” screen may still reveal blurriness on a 17” monitor or print
LCD’s that swivel out are useful for stealthy candid shots, and for unusual angles (reaching up high or down low)
One drawback of SLR digitals is that since the mirror deflects the light through the viewfinder, the image is not hitting the CCD until you actually take the shot. Therefore you don’t get to see through the lens on the LCD screen, which you do on all the cheaper non-SLR’s. (There are now some Digital SLRs with the ability to see through the lens on the LCD screen.)

LCD screen and Viewfinder