The Canon EC-1Ds Crop Lines Focusing Screen Set consists of two screens, one delineating a square format and the other a 4x5/8x10 format. The Crop Lines set, as the name suggests, is comprised of screens with the aspect ratio area marked with a thin border. The screens are based on the standard focusing screen for the 1Ds (Ec-CIII), but incorporate a crop line to aid in shooting to a fixed aspect ratio. Both screens are otherwise identical to the standard screen and no adjustment is required for proper ambient or flash metering.