"They were behind Chelsea Park now, in a place called Camera Square, where the shops offered fancy optical goods: talbotypes, magic-lanterns, phenakistoscopes, telescopes for the amateur star-gazer." (pp. 211-212)
The phenakistoscope, invented in 1832, was a precursor of the zoetrope, an item most of us got to play with in third-grade science class. A phenakistoscope involved two spinning discs and a mirror, which is why it fell out of favour when the mirror-free (and multi-user-friendly) zoetrope came into greater use in the 1860s. I have a hard time imagining what kind of "market" might exist for things like this past a children's toy or a clever handmade gift (if you've enough artistic skill to make one) -- then again, huge audiences would gather to view Dioramas in the 1800s, which involve about as much storyline as zoetropes and their kind, so what do I know?
Image of a phenakistoscope animation from Wikipedia. (There's also this great little page, which includes some sample disc animations.)
The inventor of the Diorama, of course, was Monsieur Louis Daguerre, famous for a little thing known as photography. William Henry Fox Talbot, inventor of the aforementioned talbotype (or calotype, as he named it), was technically the first to get it right, but because the daguerreotype was more popular, Daguerre (along with his sidekick Nicephore Niepce) tends to get the recognition. The rough of it is that the daguerreotype was faster and clearer, but Talbot's process involved the negative/positive process we use today, which makes it much easier to copy a photograph. (FYI, the photographs I've used as examples here are not nearly as clear and precise as later ones, when the methods were perfected.)
Widely acclaimed as the first photograph, Niepce captured this in 1826 and titled it View from the Window at Le Gras.
I'm not entirely certain what these camera shops are selling: finished photographs, negatives, or unexposed papers soaked in silver iodide? The book is set so soon after daguerreotypes and talbotypes were announced that I have a hard time seeing either of those methods assuming the state of curios and being deemed fit for child's play. The processes were still expensive enough to maintain a higher-class dignity. I also find it strange that most business cards and posters in the book use an illustrated portrait method that fits the pointillist style of the Difference Engine's printers, one that I assume would require a human artist, rather than a photographic portrait modified into pointillist form. That's the sort of expensive work I'd expect people to clamour after.