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The Essence of

Digital Cameras


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Some aspects related to digital cameras are covered elsewhere regarding general considerations about resolution and DPI etc. However, many people are puzzled by references to a camera's ''Mega Pixel'' specification.

Here we look briefly at this and a few other relevant camera matters. Actual picture taking is dealt with on another page.

Digital Camera ''Megapixels'' etc-

To figure out what size prints you can make from today's digital cameras, you have to first break down the pixel measurements.

For example, a 3.34 megapixel camera works out to give dimensions of approximately 1536 x 2048 pixels, while a 2.24 megapixel camera works out to give approximately 1280 x 1600 pixels. Note however ....... the quoted pixel dimensions you may have specified by the maker, when multiplied, will not usually quite total the megapixel figure - this is because a small number of sensor positions on the CCD (charge coupled device) are needed for registering factors such as brilliance etc.

For a reasonable quality prints, 72 DPI will ''do'', as long as image not being resized much, 150 pixels per inch of resolution is more versatile and recommended for web use where resizing often needed. For professional quality prints you may usefully employ double that, if a quality printer is also available. For simplicity's sake, pick either the long or short dimension of the print/camera resolution and work with that one. Note here, the lack of need for especially high resolutions when printing on domestic quality printers.

For these examples to follow, we'll use the long edge of the print. Let's work through a couple : -

Maximum print size (medium quality) for a 2.24 megapixel camera --1600 (the long image dimension with 2.24 megapixels) divided by 150 (pixels/DPI) = 10.7." Using this example, you could get a medium quality print of up to about 10 inches (so you could get a medium quality 8"x10")

Maximum ''pro'' quality print size would be 1600 divided by 300 = 5.3". In this case, you'd be able to get a pro quality print at 3.5" x 5". Maximum print size (medium quality) for a 3.34 megapixel camera -- 2048 (the long image dimension with 3.34 megapixels) divided by 150 = 13.65", so you'd be able to get a medium quality print of close to 11" x 14". Maximum pro quality print size would be 2048 divided by 300 = 6.8." In this case, you'd be able to get a pro quality print at 5" x 7."

Keep in mind ........ these guidelines are not absolute! Your lens, lighting, CCD quality and method of printing all play a huge part in the final results. Also, the resolutions quoted are based on optical resolution and not interpolated (upsampled) resolution. The formulas can be applied to cameras of any resolution, or you can work the formula backwards to find out how many megapixels are required to get the image quality you require at the size you will be printing.

There are many cameras available now - even 5 Mpix are within reach. For most though a 3Mpix will get the job done, particularly if 150 DPI or better.

Remember too -- if your images are only required for web use, then you can keep sizes well down anyway... meaning shooting with a 6 Mpix camera is really not necessary.

To help with choosing a new digital camera ... go to THIS PAGE for some links and further suggestions ... opens in a new window.

Brief function synopsis -

Initially, your image is passed through a lens, like most cameras and that image is then eventually focused on a reading device. Control of light passed is by a form of shutter ..... that opens enough to pass the required light level after a sensor has ''read'' the scene.Beam Splitting Schematic

Your digital camera has some similarities to a scanner, in part ... particularly in as much as, the image is passed through primary color filters to break it up into the three main components ......Red, Green and Blue. These are then ''projected'' onto a CCD (charge coupled device) usually, where levels of intensity in each color component are read as a voltage level. The analogue signal from the CCD is then converted to digital via an A to D converter and stored within the memory after processing by an on board processor chip.

That processing will often include the imposition of various algorithms to enhance, sometimes simplify, and also compress the image down in size - usually to a JPG format.

General digital camera matters -

Types of memory card -

Many cameras available nowadays, particularly the less expensive, make use of their own type of memory card. Now these work fine but, it is well worth while considering a camera which uses a standard ''compact flash'' memory card. The reason is, these are the same as used with many laptop computers, where they plug in to a small socket called the ''PCMCIA'' interface. They then behave like a small removeable hard drive. They are often now the cheapest too.

A company called ''Sandisk'' markets a very inexpensive device which will operate via your PC's USB port, called an ''Image Mate'' ..... somewhere around $25. The advantage then is that when you have shot a load of pic's, you plug in the flash card and upload your files in a couple of seconds ......... as against many minutes using a serial interface.

In more recent times however - further improvements in market availablity now see multi card readers available for simple USB use - and these will handle about any memory card out there! One of these will probably only cost around $30.

Zoom options -

Choose your camera carefully if you want a zoom facility. The only ''real'' zoom is optical, which means the lens is capable of changes in focal length ........ typically (in 35mm camera terms) about 35mm to 70mm (2:1), or on more expensive versions maybe 35mm to over 100mm (3:1).
Many cameras offering zoom in fact only give ''digital'' zoom. All this does is take a portion of the normal (let's say - wide angle view) ....... and cut out a piece. This is no different to taking a whole image and cropping out a ''chunk'' in your computer image software later. So, smaller picture but resolution no better. It will not usually look very good unless the original was taken at a high resolution.

Power Source -

When a camera has it's LCD screen in use, the current drain on batteries is very significant. Most will quickly go into a ''sleep'' mode if not used for a while but, there is little more frustrating than losing power at a critical moment!! Furthermore, use of flash will also hasten the discharging of batteries. Choose a camera which allows use of removeable ''AA'' size cells.

As an absolute minimum, you should use high capacity alkaline cells but these are generally ''throw away'' and are expensive. Your next choice is to use rechargeables. NiCd (Nickel Cadmium) types are common (typically, ''AA'' size NiCd's have a capacity rating of around 600mA to 700mA) but nowadays it is best to invest in NiMHi (nickel metal hydride).

These latter have a capacity often over twice that of a NiCd and also do not suffer the ''memory'' effect either....... which means you can top them up more safely, and not have to worry about deep cycling them to maintain full capacity.

Cameras which seem to only offer the use of Lithium replaceable batteries are not I feel very worthwhile. Replacent batteries are expensive even if quite good for duration.

What should I buy? -

I cannot and would not recommend specifics .... only suggest you give consideration to some of the suggestions above. I will just remind you though that for the most part - you get what you pay for. Very broadly, I consider that to get something sufficiently useful and with adequate quality, your budget should go no lower than $150. Better if possible to aim at the $250 to $300 region, and above. Just my thinking.

Just a reminder - if you have not already visited THIS PAGE take a look at some more camera choice factors and some links which might help also.

So - a very skinny look at digital cameras. A look around on the web will give a whole heap of information but hopefully the above will give you a kick start if new to the subject.

If looking to buy, then a trip to could well put you in the right places for good deals on prices, but do pay attention to specifications and buy carefully. Makes like Cannon, Fuji, Nikon,Kodak etc are all well worth some extra expense. Cheap can often be money wasted.

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