If your budget is limited and you are only beginning to practice underwater photography, we would recommend not taking your DSLR underwater.
A DSLR housing is bulky, cumbersome and expensive. In many cases it’s an overkill for the average diver & photographer going on 1-2 trips a year. Going for a cheap housing to save money could put your precious DSLR and lenses at risk.
Starting off with an underwater compact bundle or dedicated underwater camera might be better to begin with and as you gain more experience and start to feel limited by your gear, you can consider upgrading to a DSLR system.
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