Here is the full list of all 46 Viewfinder achievements. It takes around 5-6 hours to unlock all of the achievements on Windows.
Complete all the optional challenge levels
Complete the game
Complete the simulation shutdown sequence
Drop a battery onto your head
Go for a walk in the barcode forest
Ride the train to the final hub world
Complete the picture frame levels in chapter 4
Take 100 Photos
Complete the illusion levels in chapter 3
Find all the mahjong tiles in chapter 3
Get behind the waterfall
Drop a Dustin off the level
Release all the blueprint Dustins
Take 25 photos
Ride a balloon
Try duplicating Cait
Get the camera
Put down both playing cards
Ride the train
Find all the ducks in chapter 1
Place a photo while falling and land on it
Return to the hub world
Break the only teleporter
Pet Cait
Drop a battery off the level
Make the maximum possible number of batteries in the first camera level
Break the cartoon rope bridge
Collect all the camera filters
Find all the magnets in chapter 2
Find all the planets in chapter 4
Beat a level in less than 10 seconds!
Put the three paintings where they belong
Draw using the green pencil
Make an army of Dustins
Slice a Dustin
Place the recursive photo 15 times
Grow the flower to attract a bee
Get multiple jump powerups
Get the jump powerup
Carve the melon repeatedly
Get tricked twice in a certain level
Complete the third level without touching the battery
Rewind for a really long time
Make a choir of screaming people
Complete a timer level with only a fraction of a second to spare
Break the windmill inside the painting