CHG_CANON wrote:
Honestly, you should capture in the full pixel resolution of the (assumed) 3x2 aspect of the Canon sensor. Then, crop the file during your post processing, specifically to the composition you want to print or otherwise share. To change in the camera, consult your camera's manual and find topic 'aspect ratio' where the steps will be explained.
I agree with Paul... shoot in your camera's aspect ratio whatever that is, 3:2 for most full frame DSLR's, otherwise you are throwing away pixels. Change you aspect ratio in your post processing software using the crop tool.
I tried to post a link to an article about aspect ratio that explains it in pretty simple terms, and how it affects print size and uploading to different websites such as Instagram, Facebook, etc. Unfortunately, UHH prevented the link from posting. You can go to the website Phototraces and use the search function for aspect ratio if you want to read the article.