The Polaroid Land Film Holder #545 is a film holder for 4x5" large format view cameras. It can be used like a common film holder, clamped between matte screen frame and camera, but it is much heavier. That's because it's used with Polaroid's special 4x5 enveloped instant film sheets. The film holder doesn't take the common Polaroid film packs. It's just usable with single sheets of that special enveloped instant film which was available until ca. 2005 . Ca. 12 different variants of that film were made, with film speeds from ASA 50 to ASA 3000 for black and white positives on paper, and in a smaller speed range for color positives on paper, and one version for making black and white negative and positive at once (the negative needing an extra fixing bath).
Before usage the image must be focused with help of the camera's matte screen. Then the shutter must be closed and set to an appropriate shutter-speed/aperture combination. The big lever over the film holder's film load slit must be in position L(oad). Then the film sheet can be pushed into the slit, of course with the envelope's side marked "this side towards lens" towards the open front of the holder. Then the holder must be clamped between matte screen frame and camera, naturally with the open front towards the camera. The brief instruction on the holder's closed back becomes visible through the matte screen. Before exposure ca. 4/3 of the envelope must be pulled out of the slit. After exposure the envelope must be pushed back. Then the big lever comes to action. It has to be set to P(rint) position. Then the envelope must be pulled, this time smoothly but with slightly more power. Inside the envelope is another much smaller envelope which contains the film development liquid. Pulling out the film envelope in the film holder's P mode means that the chemical is pressed out of the small inner envelope and spread over the exposed film sheet. The envelope might not come fully out of the holder but at least 90% of it. Then the big lever must be put back to L position for release. The envelope must be opened after the development time which is depending on the actual surrounding temperature. A list of development times for some temperatures is printed on every envelope.
There's a trick to make development later than the photo session. Removing the envelope with the enlighted film without putting the big lever into P position before. Therefore the little lever over the P position must be pushed when pulling out the envelope. At home the envelope can be pushed back into the slit, then the big lever has to be put to P position, and the enveloped film pulled out for development. The mechanics of the film holder must be cleaned from time to time.
An alternate film type was available: Common film sheets, enveloped but without instant developer onboard. That was because the envelope loading method was a smart daylight film load method for large format photography.