Each area in New Pokémon Snap has its research rank. As you take pictures of Pokémon and make discoveries in each area, the research rank for that area increases, which will unlock new Pokémon, situations, and items.
The rank will certainly increase faster if you take pictures of new Pokémon that you don’t already have in your Photodex since that will typically provide more experience points, but it goes with everything you do. You can provide Professor Mirror with a picture for each Pokemon you encounter in a course, whether you’ve provided data for them already or not.
You should look for new Pokémon and try to get better star ratings along the way, but take one picture of each kind of Pokémon while you shoot for that goal. Even if the picture isn’t better than the ones you have on file with Professor Mirror, you will still earn experience points.
That means that you can get experience points for each Pokémon available in the area with every run you do. Maximize your experience gains by using that film and snapping as many pictures as possible. It’ll help make you a better Poke-photographer, but it’ll also help you level up faster. As you level the research rating up, new Pokémon will appear and sometimes existing Pokémon will do different things, which will provide you with higher star ratings.
It may seem broken, but it’s exactly as the game is supposed to work. New Pokémon Snap isn’t about taking only perfect pictures — it’s about discovering the behaviors and abilities of Pokémon and seeing how they live among each other in the world. Your character is a researcher, not an artist. Thankfully, the game also has a great photo mode and surprisingly good online features for a title published by Nintendo, so you can still be an artist on the side.
But while you’re leveling up and making discoveries, play it like a researcher and capture as many pictures as possible. Just make sure not to accidentally replace your Photodex photos when Professor Mirror is evaluating them and handing out scores. You will definitely capture better pictures while you hone your skills and level up, but they won’t all be better. You’re snapping as many pictures as possible, so quality is a secondary focus.