How does the auto exposure on Polaroid 420 or 450 work?

[Paul Howell]

I'm in the process of converting a Polaroid 420 to a 6X9, looking at the camera there is a metering cell, the shutter is manually cocked, a selection for either ASA 75 or 3000, (the 450 also has 150 setting as well). I've order the battery, just looking at the shutter it seems to a fixed speed, so the aperture is controlled? My parents had a 450, seemed to do a good job in most lighting. Anyone know how it works?

 

[Donald Qualls]

From my experience converting a 210 to pinhole (3000 speed film only) and keeping the auto exposure, the entire 100-200-300-400 family 3x4 pack film strut folding family uses the same exposure system:

The shutter will snap without a battery, but will not actually open; with the correct battery, however, it opens when triggered and starts "counting up" exposure until it has enough, then closes the shutter; speeds seem to range from 1/250 (maybe faster on later models) to at least several seconds on the early ones, and more than a minute for a 350 (might run longer still on a 450; the first gen SX-70 used essentially the same method and could expose for up to two minutes). I've seen this behavior on a 100, 210, and 350 that I've owned, so I believe it's universal across the entire family for the twenty or so years they were made (though some want 3V and others need 4.5V -- in identical size/shape batteries).

 

[Paul Howell]

Thanks, very helpful.

 

[ic-racer]

Diagram from the repair manual to show the function:

 

[Paul Howell]

New battery arrived, the shutter works as designed, tomorrow or Monday will use a 4X5 sheet of Foma 200, rate it 100 and use the ASA 75 setting to see what kind of negative I get. If it seems workable will start to remove the back starting hunting for a machine shop to make the adaptor plate.

 

[eli griggs]

Good luck.