Drape your table with the black cloth in an outdoor area that receives full sunlight. Black cloth works because it offers few reflections to compete with the sparkling light coming from opal.
Place the opal on the cloth. Move the opal around until you find the gemstone's best angle for photographing.
Attach the digital camera to your tripod. A tripod keeps your camera steady, so you get a clearer photo.
Set your camera's exposure two to three stops higher than the lowest setting on your camera. The higher exposure allows you to capture the fire in the opal without making it too dark and unattractive.
Look through the viewfinder to see how the opal looks. If you're using a zoom lens, move the lens in and out to find the best lens length for photographing the opal. If using a fixed lens, move the camera close or farther away from the opal to get the right distance.
Move the opal around to find the best position through your viewfinder. Opals produce more reflective color in some positions than in other positions. Find the right angle from which to shoot so you get the best photo while showing the stone's abundant color reflections.
Take a photo, then review it in your camera's LCD screen. If the photo needs improvement, make adjustments to the placement of the opal on the table or to your camera's exposure. Take another photo and check it to see how your changes effected the image of the opal.