This was a hot topic on one of the popular photography forums last weekend. Aspect ratio is the ratio of the length of a rectangular shape to its width. If the length is equal to the width, then the shape has a 1:1 aspect ratio. 5184 by 3456 pixels is 5184 / 3456 = 1.5, or expressed as an aspect ratio, 1.5:1. By convention, whole numbers are preferred, so 1.5:1 would be written as 3:2, Simple mathematics.
A digital camera's sensor aspect ratio is the width divided by the height, in pixels. For the Canon 60D, which has a RAW image size of 5184 x 3456 pixels (18.0 MP), this is 5184 / 3456, or 3/2. The accepted notation for aspect ratio is 3:2. Thus for the Canon 60D, 3:2 is the native aspect ratio. All RAW images are captured and saved with this aspect ratio by the 60D, preserving every possible pixel, regardless of the aspect ratio you might choose in the menus.
A digital camera's sensor aspect ratio is the width divided by the height, in pixels. For the Canon 60D, which has a RAW image size of 5184 x 3456 pixels (18.0 MP), this is 5184 / 3456, or 3/2. The accepted notation for aspect ratio is 3:2. Thus for the Canon 60D, 3:2 is the native aspect ratio. All RAW images are captured and saved with this aspect ratio by the 60D, preserving every possible pixel, regardless of the aspect ratio you might choose in the menus.
Most DSLRs let you choose the quality of the image to be saved. Options typically include one or more RAW (the camera's native format) selections, and one or more JPEG selections.The Canon 60D allows you to save in RAW only, JPEG only, or RAW + JPEG. There are also settings for image quality: higher quality means more data saved. This means you use more storage space per image, and therefore your storage device cannot store as many images. I always save in RAW at maximum quality. You can always convert the RAW image to JPEG or another format with your computer.
There are camera menu options that allow you to select among the aspect ratios 3:2, 4:3, 16:9 and 1:1, but these are only used in the Canon 60D if Live View mode is Enabled. Anything other than 3:2 will reduce your effective MP count for JPEGs only. You are trusting the camera to crop your JPEG images for you, but if you are also saving RAW you will still capture the whole image. If you leave Live View disabled, cropping is ignored. At maximum quality in Live View mode on the Canon 60D, your JPEG megapixel counts are as follows:
3:2 is 5184 x 3456, or 18.0 MP
4:3 is 4608 x 3456, or 16.0 MP.
16:9 is 5184 x 2912, or 15.1 MP.
1:1 is 3456 x 3456 pixels, or 11.9 MP.
The Canon 60D and other advanced DSLRs can do a lot of other in-camera image processing as well, but I prefer to do all post-processing on the computer. With good image processing software such as Photoshop, you can achieve any aspect ration that you require, but that is a topic for another day.
Here is a photo of a flower in the park. While it looks simple, getting the exposure just right was key: it was just after dawn under a totally overcast sky. A tripod was necessary to keep the camera steady during the exposure.
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