If you're planning a beach photoshoot near Lisbon, you need to know that there is no ocean within the city reach - only the river Tagus. Thus, to get to the ocean you need to leave the city and drive to other places. Also, I wouldn't recommend the public beaches in Carcavelos, Estoril, or Cascais for photoshoots
In the last years, Praia da Ursa has become quite popular among tourists. So, it's not a hidden place anymore, but still not a crowded one due to its hard access. Which is actually good, as you can enjoy some peace and feel the power of the ocean with no distractions. It is hard to describe all the