Coming across a bat ray or two on your dive is an exciting underwater event. They are such interesting creatures with strange faces and a unique way of propelling their way through the water that is more akin to flying than swimming. While I often find them motionless on the bottom, they can be difficult to approach and photograph because of their skittish nature. Here are a few tips:
While not uncommon, you definitely do not see them on every dive. Their range is from Oregon to Baja but you will most commonly see them from Monterey south. Although you will see them “flying” over rocky reefs and through kelp forests they rarely settle there. They prefer shallow sand and mud flats in quiet bays and coves. That is where you will want to look. Our personal favorite location is Little Geiger Cove on the frontside of Catalina Island in the late summer when they congregate to mate and feed on the abundant fat innkeeper worms they love so much. On a recent dive we came across over a hundred bat rays 4 to 6 feet wide lounging on the bottom in the sea grass in 20 to 25 feet of water. Other good locations include Marine Room in La Jolla, some of the sandy coves of Laguna Beach (although most of these rays are small), and Malaga Cove and adjacent nearby RAT Beach at the south end of the Santa Monica Bay. 
Here is where it gets tricky. Bat rays are notoriously skittish and bolt at the close approach of the diver. Because they are most commonly found in shallow sandy and mud bays, water clarity is an issue and for a decent photo you will need to get close, preferably less that five feet or less. Here is the key: get low and approach slow. Low and slow. If you are too far off the bottom your shadow or silhouette will trigger a flight response from the ray. 
Once you have found a ray and are creeping across the bottom for the approach, there are some key behavior patterns in the ray that will tell you they are ready to take off quickly. First, they will raise their tail high and tall. Second, they will come up off the bottom propping themselves up on their wings. At the sign of their readiness to swim off freeze and stay low and most of the time they will settle back down on the bottom. Give it a minute or two, and then continue with your slow approach. Once you get close, shoot away to your heart’s content. They do not seem to be bothered by strobes.
If possible, include a diver in your shot to show the perspective on large rays. The model, however, also has to be aware of the techniques of approaching low and slow.
Sometimes it is actually desirable to alert the ray and have them assume a propped up position. This gives you the opportunity to photograph their mouth and underside. Be aware, however, you may only get one shot of this behavior as they will fly off quickly. Another one-shot opportunity will be as they fly off in a hurry.
Because they are found on sand and mud flats, you will need to use your best techniques to minimize backscatter. On top of that the rays like to stir up the bottom and they bury themselves or feed. Keep your strobes wide, at an angle, and your background exposure light. 
Wide-angle is a big plus because of the poor water clarity and often the large size of the rays. Because of the often poor water clarity you will need to get close for the best shot and it will allow you to get the entire ray in the shot. If you are using a point-and-shoot camera, get a supplemental wide-angle lens. Normal lens and even macro photography is not out of the question if you can get close enough as rays have very interesting eyes and faces.
Successful shots of large bat rays, especially with divers in the background will dazzle your friends as to the wonders of the California seas. Go for it by looking in the right places, approaching properly and using the right camera techniques. 
California Diving News