35mm slides have an image dimension ratio of 3:2. Many compact digital cameras have a squarer ratio than this, or you may have deliberately cropped your image to something of your chosing. By default we don’t crop your image to fit the 35mm frame – any excess left and right (for a squarish image) or top and bottom (for a thin landscape image) is automatically filled in with black. When projected you don’t see the black bars of course – black is the absence of light – and all you see is your image the way you created it.
However, if you don’t want this then when you order your slides you have a choice of ‘Crop to fill frame’. We will then crop the image (which we will do by eye to avoid inappropriate cropping of your image) so that the full slide area is utilised. Note that images are never stretched or distorted to make them fit, just cropped.