Hulking Attachment Gave Canon FD Lens Autofocus 40 Years In the past

The Canon Zoom Lens FD 35-70mm f/4 AF was a lens initially manufactured in 1981 and options an uncommon motor system that allowed it to autofocus. In Kai Wong’s 13-minute video, he reveals the way it nonetheless works remarkably properly even at present.

Noticed by Fstoppers, the FD 35-70mm f/4 AF took Canon’s profitable lens and added a big field above the lens which housed a mechanism that may permit for autofocus. It used Canon’s Stable State Triangulation (SST) system that initially appeared in the AF35ML compact digicam that additionally launched in 1981.

In response to a narrative on MIR, the SST mechanism used triangulation to measure capturing distance. The measurement is carried out by observing a topic from two factors, therefore the 2 small lenses which might be seen on the entrance of the big autofocus field of the FD 35-70mm f/4 AF. The 2 factors have been barely angled in order that incoming gentle rays that may bounce off a topic would are available in and be triangulated by a small CCD picture sensor contained in the system. Canon describes it as such:

The SST methodology is a system through which info on the photographed object that enters the sensor by means of two mounted mirrors is transformed into an electrical sign and distance is measured by a microcomputer, with focusing carried out by shifting a distance ring with a motor. The newest mounted imaging machine CCD (charge-coupled machine) know-how is adopted to offer excessive decision and a broad dynamic vary in a position to detect low to excessive luminance, making it much less inclined to the distinction and sample measurement of the photographed object and enabling extremely exact autofocusing. Additionally, because the SST methodology doesn’t have a movable part within the distance measuring mechanism, no vibration or electrical noise is prompted, which gives excessive reliability becoming of a high-end SLR digicam.

The system, as evidenced by Kai’s video above, works remarkably properly. Whereas he’s utilizing a mount adapter, on the time the lens was suitable with any Canon FD-mount digicam, making autofocus one thing anybody with such a digicam able to upgrading to an autofocus lens.


The corporate would later use the same system for the FD mount of the Canon T80 in 1985 which was in a position to autofocus with one in all three lenses that had built-in autofocus motors. Canon would ultimately abandon autofocus on the FD mount because it moved in direction of the EOS system in 1987.

Whereas the system clearly works properly, its implementation on the 35-70mm f/4 lens has a transparent draw back: it’s enormous and hulking. Whereas it isn’t significantly heavy, it’s a cumbersome addition to a digicam system that may have usually been a lot smaller and simpler to move. Whereas the know-how behind the autofocus system nonetheless works, it has since been changed with strategies which might be much more compact.

For extra from Kai Wong, be certain that to subscribe to his YouTube channel.

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