Here is the full list of all 46 Viewfinder achievements. It takes around 5-6 hours to unlock all of the achievements on Windows.
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
Complete a timer level with only a fraction of a second to spare
Release all the blueprint Dustins
Place a photo while falling and land on it
Take 25 photos
Break the only teleporter
Ride a balloon
Slice a Dustin
Make an army of Dustins
Drop a Dustin off the level
Try duplicating Cait
Make the maximum possible number of batteries in the first camera level
Get the camera
Drop a battery off the level
Ride the train
Place the recursive photo 15 times
Return to the hub world
Pet Cait
Drop a battery onto your head
Get behind the waterfall
Break the cartoon rope bridge
Collect all the camera filters
Find all the ducks in chapter 1
Find all the magnets in chapter 2
Find all the mahjong tiles in chapter 3
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
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
Put down both playing cards
Complete the simulation shutdown sequence
Complete the game
Complete all the optional challenge levels
Rewind for a really long time
Make a choir of screaming people
Break the windmill inside the painting