When importing files that are not the same aspect ratio as the project you are creating, Premiere will resize the files to the ar of the current project. This can severely distort the image if the aspect ratio differs significantly from the project it is imported into.
In the example to the right, the mushroom explosion is 800 x 1400. It was extracted from a 2k film image to give full film resolution in a near video format. The height allows the explosion its full range without cutting it off or reducing it.
However, when importing into a 4:3 Premiere project, it gets resized to 720 x 486 effectivly 'squashing' the image.
With the 'Lock Aspect' preference selected, the original image format is retained.
You should know the file size of any sequences you want to use in a Premiere project. Any sequences that are not the same aspect ratio as the project should be imported after you have checked the 'Lock Aspect' preference box.
