Aspect Ratio explained
In theory, the aspect ratio is quite simple to explain in that it is the ratio of the length to the height of the image.
Hence our well known “normal” 35mm film size was 36mm x 24mm which is a ratio of 3:2.
In fact, the term “35 mm” relates to the total WIDTH of the 135 film itself including the area either side of photo width including the sprocket holes.
Image courtesy of Wikipedia
Of course even before Oskar Barnack invented the 35mm format, there were other formats in use and 10 inches x 8 inches (10x8) was the size of sensitised glass plates that were originally used for many of those first historic images and this is a 5:4 ratio.
Later, 10x8 inch and 5x4 inch sheet films became popular due to easier handling and convenience - which maintained the 5:4 ratio used by many famous photographers such as Ansel Adams.
As film stock and processing improved, some photographers wanted to break away from this somewhat restrictive 10x8 and 5x4 large formats and hence the move to more portable cameras such as the one we know – 35mm - originally known as miniature format!
Around the same time other photographers wanted a higher quality negative with greater resolution and so other medium format films were developed such as 60mm x 45mm (645) 12:9 ratio, the 60mm x 70mm 6:7 ratio and the 60mm square 1:1 ratio typically seen in the Hasselblad - which was developed in 1957- became popular.
The two main features of the 1:1 ratio seen in the Hasselblad were the ability to see the image differently and due to the square nature of the image, to be able to crop later if required. For example the 1:1 square crop sometimes works well for flower details
Another crop often favoured is the 16:9 panoramic crop which is great for landscapes.
So what does all this mean for us today? Basically, it means that with our Full Frame 36mm x 24mm digital sensors we now have the ability to shoot in the 3:2 ratio and then crop afterwards to the ratio which suits the feel of the image we want to produce.
Clearly other smaller size sensors such as 4/3rds and APS-C are also very popular and due to the amazing technological strides made, great results can also be achieved with them.
In most of our digital cameras today we have the ability to select different aspect ratios to assist us in ‘seeing’ the image in the way we wish to present it to ourselves and others.
Just remember that by cropping ‘in-camera’ you will be throwing away some of those pixels which would have been there in the “native” 3:2 ratio of modern cameras.