T90 Shutter: The Movie (Magnets Visualized)

<p>OK, not a movie. I've been meaning to do this, so I finally did, reminded by the recent "flashing arrow" thread. This is a defunct T90 shutter that's been lying around in a box of parts for years. I took some photos this evening so everyone can see the infamous magnets.</p>

<p>Photo 1: the entire shutter assembly. Curtains run in a frame about 3mm thick. The high-rise structure at the end is the charge and release mechanism. It houses what must be 100 different springs, levers, pawls, catches, shafts, gears, the two release magnets, and the switch for flash sync. The large lever that protrudes is operated by the motor drive at film advance to charge or cock the mechanism prior to exposure. The flex circuit on top carries five transistors, at least two of which would be drivers for the release magnet coils. The "tail" on the flex circuit wends its way up to the top of the camera, where five connections solder to the main circuit and I believe two to the hot shoe.</p><div></div>

<p>Photo 2: a closer view of the flex circuit and the shutter-side of the mechanism.</p><div></div>

<p>Photo 3: opposite side of the mechanism. The release magnets are at the top, identified by their copper windings. Below them are black plastic worm gears on long shafts, which engage spur gears that adjust curtain spring tension. If you look closely, you can see that the plastic worm is broken off on the left side. That's for the second curtain. It no longer has proper spring tension and only closes about halfway. I don't know whether that gear failed from stress, or if it was damaged after the shutter was removed from the camera. I hope it was the latter.</p><div></div>

<p>Photo 4: First curtain magnet labelled, second curtain magnet held open. Remember that the T90 uses permanent magnet cores. Only a brief electrical impulse is applied at exposure to buck the permanent magnet's field to make the armature move. It takes a surprising amount of force to pluck it off of the core by hand, like I did here. (Note the armature gap I'm holding open on the left magnet; that's where they stick.) I don't claim to know what causes them to "stick." Maybe magnetization of the moving part, maybe some sort of sticky film, maybe black magic.</p>

<p>I have the mirror box as well, but cannot find it tonight. When I locate it, I'll add it to this thread, but its sticky magnet looks essentially the same.</p><div></div>

<p>That's most interesting, thanks for posting. These must have been very expensive and difficult to make.</p>

<p>Thanks for posting this. I probably have a weird aesthetic, but that mechanism is just beautiful! </p>

<p>Alan--thank you! An incredibly complicated mechanism--must have been costly to build. How much were T90s when they were new? Thanks again!<br>

Paul</p>

<p>My pleasure. I think a lot of us take aesthetic pleasure in beautiful machinery. My latest quirk has been a search for a lathe. I enjoy seeing the 1940s-era Monarch lathes. They are attractive in their way, a statement of precision in strength and latent power. I'd seen pictures, then happened to stumble onto an actual example locally, about 14 feet long, probably weighs 11,000 pounds. Its designers made no real attempt at beauty or style, but it is still attractive.</p>

<p>Paul, search this forum for a thread entitled "Original Prices?" It contains a discussion of a lot of items plus some scans of old ads.</p>

<p>Alan, this is my personal tribute to a great camera, the T90.<br /> <br>

http://canonfdworld.blogspot.it/p/la-canon-t90_2.html</p>

<p>Imagine...all of those spring and gear jiggums moving to give a 1/4000s shutter speed!!</p>