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 exhibits the way it nonetheless works remarkably nicely even at the moment.

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 might enable for autofocus. It used Canon’s Stable State Triangulation (SST) system that initially appeared in the AF35ML compact digital camera that additionally launched in 1981.

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

The SST technique is a system during 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 transferring a distance ring with a motor. The most recent mounted imaging machine CCD (charge-coupled machine) expertise is adopted to supply excessive decision and a broad dynamic vary capable of 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 technique doesn’t have a movable part within the distance measuring mechanism, no vibration or electrical noise is brought about, which offers excessive reliability becoming of a high-end SLR digital camera.

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


The corporate would later use an identical system for the FD mount of the Canon T80 in 1985 which was capable of autofocus with one among 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 nicely, its implementation on the 35-70mm f/4 lens has a transparent draw back: it’s big and ponderous. Whereas it isn’t notably heavy, it’s a cumbersome addition to a digital camera system that might have usually been a lot smaller and simpler to move. Whereas the expertise behind the autofocus system nonetheless works, it has since been changed with strategies which are way more compact.

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