POLAROID sonar focussing

Polaroid SX-70 Land Camera

With sonar focussing, Polaroid introduced an instant auto focus system for their SX-70 instant film cameras. It is described in the user manual as follows:

“As you begin to press the shutter button, your camera releases sound waves to the central part of the scene. The frequencies are far beyond your range of hearing and travel at the speed of sound. The split second it takes for the sound to reach your subject and the echo to return is fed into a tiny electronic computer inside the camera. The computer uses this time measurement to calculate the distance between the camera lens and your subject, then signals a motor to turn the lens until your subject is in sharp focus. This extraordinary chain of events take place in less than 1/3 of a second”

Source: Polaroid SX-70 Manual PX1492 7/78, Printed in U.S.A.

I really like the descriptive nature of the manual. Not that I am into reading manuals at all, but compered to current manuals for anything, this is quite nice to read. One has to consider that this new technology was a breakthrough feature and new to anyone using it.


Source: Polaroid SX-70 Manual PX1492 7/78, Printed in U.S.A.

Since sound waves behave the same all day, the system can be used in the dark. The use case of focusing in low light situations is not that relevant to me, since I am not about to try flash bars with my Polaroid camera any time soon. The instant film available today has better photoresponse than pervious material from Polaroid, but still is not suitable for any real low light situations in my (somewhat limited) experience. Although sonar focussing was a very innovative in the 1970ies, active auto focussing systems have some disadvantages one should be aware of. They can obviously not focus through windows, since the sound waves can not pass through glass. After some tests with my SX-70 I can attest that the focus system is also not very precise and fails to focus subject close to the camera entirely. So one might end up using manual focus after all.

On a personal note: the sonar focussing module can not be removed from the SX-70, which is quite a downside, since it does not fit the pleasing aesthetics of the camera’s body.

Polaroid SX-70 Land Camera
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Edwin Land

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