The new kit has been announced at the Ifa tech show in Berlin.
The idea is to add capabilities that are not currently built into handsets themselves.
But Sony's latest flagship phone also has new photography tricks of its own.
"It seems that people are holding on to their phones for longer, and, so, vendors are hoping to sell them extra things to add on," said Carolina Milanesi, a consumer tech analyst at Creative Strategies.
"And the camera is often the feature they use the most.
"But the price is critical.