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