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Use a 128MB SmartMedia card. The more pictures you can take the better!

Use rechargeable NiMH AA batteries. They're less expensive over time and reduce weight, bulk, and clutter when you're on a boat or in a confined space. If you already use rechargeable batteries with your strobes, just add a few more to your charging station. Two sets for the camera is usually sufficient. Shoot with one set while the other is charging. Then swap batteries during your dive interval. Use NiMH that have at least a 1600 mAh rating for long battery life.

Change camera batteries between dives. Some times you can squeeze out a second dive, but if your batteries exhaust 15-20 minutes into a dive you'll be bummed.
or
Use batteries with a high milli-amp-hour (mAh) rating. Olympus' 1700mAh rechargeable batteries have lasted two dives with a combined bottom time of over 120 minutes.

Use a focus light during night, deep water, and low light situations. If the camera doesn't obtain a focus lock, your pictures will be soft and lack detail (or be out of focus altogether.)

A few camera settings we recommend:

Customize the "Reset All" feature on the camera and select the sub-menu "Custom" to specify your preferred settings. When Tetra is powered on you are ready to take pictures and not waste time programming the camera.

Always turn the camera's flash off using the flash button on the back of the camera. The camera's flash is ineffective in the Tetra housing and will just consume battery power. If you are using external strobes they'll fire everytime a picture is taken and are not affected by the camera's flash setting.

Set the ISO rating to 100. Just like with film, you'll achieve better color values.

Set the Recording mode to SHQ or HQ. At these settings your image will retain their high quality for printing or photographic prints. A 128MB SmartMedia card HQ stores between 160-200 photos and is great for reproducing prints up to 10"x14". For larger prints use SHQ setting. SHQ stores about 25 - 45 photos on a 128MB SmartMedia card.

Set the "Rec View" feature to on. This automatically display the photo just taken and allows you to view the results without switching to the camera's Display mode.