Now that you can make one shots and can crudely bracket some shots, you may want to see exactly what light is getting through your lens. A ground glass plate was used to do just this in the earlier days of camera and is still widely used by professional film cameras to this day. Ground glass for a typical packfilm camera can be used to give you very specific information about sharpness of focus, framing of the subject matter, and even dialing in accessory lenses for effect. If you are a lomography or experimental photography nut, this should work well for you!
Making a “ground glass” for packfilm is simple and cheap. All you need is a piece of plexiglass, an empty pack, some sandpaper or foggy(not clear) scotch tape, and some glue-all adhesive. First take the pack apart. Set aside the part that has the foam tongue- you won't need it. Take the inside piece(film plane) and trace it onto your plexiglass. If your trace is about 1/16th or so wider and bigger than the inside piece, make sure you adjust the difference before you cut.
Now cut the plexiglass to size. I feed plexiglass slowly and methodically through my band-saw or jig saw as it tends to melt if you go too fast(it can also crack). Once you have it to size, sand the funky edges smooth. Dry fit and adjust accordingly.
Now for the “ground glass”. Either sand the plexiglass on one side until it is very foggy, or cover one side with the scotch tape(careful to leave room to glue the edges down. Apply glue to the inside rim of the pack, and stick the plexiglass to it- foggy or taped face towards the glue. Wait for it to dry and you are done!
I have also shown a fuji instax mini and a fuji instax wide ground glass I have made- just as easy!The Lomo Instant and Lomo Instant Wide use instax film(and the new Automat as well)!
It helps to have some sort of hood if the glare from the room or space is too much. An easy hood is a black tshirt with the camera poking through the neck hole and the body of the t-shirt acting as the hood. A clothespin can fasten it-simple!
Since most Polaroid cameras were consumer grade and did not have professional features like bulb, some cameras may need a little strip of electrical tape to cover up the exposure control (this will open the lens for several seconds at a time).