What is aspect ratio and why do I need to know about this?

Aspect ratio is is a term used to describe the ration between the width and the height of an image. The reason aspect ratio is often ignored is quite simple - the aspect ratio of your photos depends on the camera used, and we tend to take that for granted.  Many of the newer digital cameras provide an option to select from several aspect ratios, each of which has its own characteristics and photographers can crop an image to a different aspect ration in post-processing.

So, how does aspect ratio work? It relates to the width and height of an image and basically describes how square (1:1) or wide (16:9) or image is. It's expressed as a figure, like this: width:height (width always comes first).

Most compact cameras, some digital medium format cameras and medium format film cameras use a 4:3 ratio or similar - hence the instant print machines/mass-market labs common print sizes being 7x5in/8x10in and reproducing the image as shot by the camera. 

The aspect ratio of the 35mm frame is 3:2. All fx and dx digital SLRs, regardless of sensor size or megapixels, use the 3:2 aspect ratio. It simply means that the frame is one and a half times as wide as it is high (or the other way around if you turn it on its side to use the vertical or "portrait" format).  

Your event will be shot using high end digital SLR's (unless otherwise specified) using an image aspect ratio of 3:2 with a view to pleasing album design/large-scale printing through professional print labs.  A small number of your images may be cropped to a 5:4 ratio if it felt that it aids the image.  Therefore, your images will NOT be the correct aspect ratio to fit into a 7x5in print without cropping (reducing the size of the image by cutting some away) and please bear in mind that if sent to a lab without a preview option, it is likely you will have no control over the where the crop will fall and so important areas of your image may be lost. 

Below is a cheat sheet that lists the print sizes compatible with a 3:2 aspect ratio so that you won't go wrong when ordering prints from a third party.  Alternatively, you can always order your prints through me and I can advise what sizes will suit the image to be printed and whether it can be cropped to change the aspect ratio.

Cheat sheet and more information regarding aspect ratio can be sourced at paintthemoon.net.