DVMG - Fact Sheet Number-3

Fact Sheets Index

Digital Photography

Tony Miller


Newcomers to digital photography are often confused when trying to compare their 35mm equipment with the digital equivalent.

For instance, the image capturing device or sensor used in a digital camera is somewhat smaller than the area of a 35mm frame so the focal length of the lens required to capture the image is also less.

An easy way to compare the two is to multiply the length of a digital lens by seven to get a rough comparison to a 35mm lens. Thus the Canon PowerShot A5 Zoom camera with a lens of 4mm to 10mm is the equivalent of a 28mm-70mm lens on a 35mm camera.

Similar confusion reigns over image quality. Digital cameras use CCD's (or charge-couple devices) to capture the picture, recording them electronically as pixels or a series of coloured dots. Image resolution is controlled by the number of pixels.

Most digital cameras allow you to change the number of pixels depending on how you want to output your picture. For instance, you need much less quality for an image going onto the Internet (generally 72dpi) than if you wanted to print a 6x4 inch print on your colour printer.

With the Canon PowerShot A5 zoom camera you have the choice of top quality images at 1024 x 768 down to low quality images at 512 x 384 pixels. To add to the confusion you then have to understand that to produce a reasonable quality print from your colour printer the image needs to be 150 to 200dpi (dots per inch). For top quality you will need an image of 300 dpi. Assuming it's 200dpi and you have chosen Canon's largest format of 1024 x 768, by dividing these figures by 200 you will get the maximum print size of reasonable quality, roughly 5x4 inches.

For further information on this neat little camera check out Canon's website at www.canon.com.au

Tony Miller. E-Mail: millert@ozemail.com.au