Expoimaging 95mm ExpoDisc Professional Neutral White Balance Digital Camera Lens Filter - Expoimaging ExpoDisc The ExpoDisc is far easier to use than any gray card, white card or calibration target. Simply place the ExpoDisc in front of your lens and capture the incident light while setting your cameras custom white balance. Using an ExpoDisc custom white balance will virtually eliminate the need for RAW or JPEG post-capture color adjustments.