This page describes how to modify the Canon T90 to have mirror lock up, MLU. At some shutter speeds, vibrations from a slapping mirror can cause unsharp images. Spesially at high magnifications. Canon engeneers didn't, for unknown reasons, include a MLU when the T90 was designed. The mirror was supposed to be dampened enough to make the vibrations insignificant. But some people report that the mirror slapping acually can cause unsharpness in images. Specially when using long lenses or at high magnification macro work.
For more about MLU, take a look at the links.
The modfication consists of installing a small printed circuit board, and connect 7 wires to different places under the top cover. Anyone with soldering experience can do this.
After studying service manual, I found a way to relase the mirror before the shutter without letting the camera CPU know. This can only be done because both the shutter and the mirror are electrically released, and independend of each other. Small permanent magnets are used for this. They are surrounded by a coil, when energized causes the magnetism to decrease enough for the magnets to drop their load. When the shutter release button is depressed, the mirror release magnet releases the mirror and when the mirror is up, a switch is activated and the camera releases the shutter.
The MLU unit tricks the camera to think that the mirror is still down, and allows the mirror to be released well before the shutter is released so vibrations can die out.
The MLU is engaged by pressing the Exposure Compensate (Exp.Comp) on the lower back side pluss the shutter release button simultaneously. The mirror flips up, and when the shutter release button is depressed again, the shutter is relased with a small click. If the mirror needs to be reset again without releasing the shutter, just press the Exp. Comp. shortly. The Exp.Comp normal function is not altered. The shutter release button MUST be released first, else the shutter will release as soon as the Exp.Comp. button is released. Also, normal programmed exposure, Tv or Av won't work. Manual, stopped down mode MUST be used. And of course, you'll be using a remote trigger and a tripod. Else it doesn't make sense to use MLU at all.
MLU is only possible when the main switch is in the "A" position to avoid releasing the mirror in a camera bag, but the mirror can be reset with normal reset procedures describes above even if the main switch is in the "L" position.
The meter won't work properly when the mirror is raised because it blocks the light sensors in the prism. Manual metering must be used when MLU is enabled. This is done by taking a metering, setting the aparture on the lens and a shutter time in Tv mode according to the metering. If the camera is in Program or Av mode, a very long shutter time will occure. Also, stopping down of the lens is normally done by the raising mirror. Since the mirror already is up when the shutter is fired, the aparture cannot be set from the camera, and must therefore be set on the lens, and the stop down lever pushed inn.
No other functions of the camera is affected, and most importent, no permanent modification on the camera have to be done. If MLU is not needed anymore, the board can be removed and the camera is back to original.
Space is critical inside the camera. To make the circuit as small as possible, a microcontroller with a onboard oscillator was used. The number of components is also kept at a minimum, with only the controller in a 8-pin SOIC package, one resistor and one capasitor. The controller is programmed to run the show. To make the controller as "stelth" as possible, it shuts down to minimize the current consumtion to only 0.5uA! It only wakes up when needed. Even when the MLU is engaged, the current consumption is negligible.
The board is made so it doesn't overload the camera circuits, nor does it alter the normal functions. An industrial grade microcontroller is used to assure operation between -40 and +80 degrees celsius.
To be able to install the circuit board safely without damaging the camera, you need some tools and soldering experience. If you don't know how to solder (electronics, not water pipes), find someone who does. Else you risk ruining a fine camera and selling it on eB*y as parts.
Tools needed:
You need a clean working space with plenty of ligth. Also a tray to keep small parts. Make a note with screw sizes and where they go.
Discalimer: I'll take no responsibility of damaging the camera after wrong connections or bad soldering, so do it at your own risk.
Remove the batteries first!!
Click on the pictures to enlarge them.
The neckstrap must be removed.. Remove the three visible screws around the lens mount. Then loosen the two screws on the back lid locking plate about two turns. Don't remove the screws completely. Open the back lid and carefully wiggle the plate loose with a screwdriver. This will loosen the front plate.
Remove the two crome screws on the front, two black screws on the back and one under the neckstrap loop on the right hand side.
Use the needle to ply out a small rubber disk on the eye piece shutter lever and remove the screw under it. Carefully lift up the top cover. There a number of small wires that connects the hot shoe to the flex board under the cover. Be carefull not to tear them of. Solder off all the wires and put the top cover away. The picture below show where the wires are connected. Also remove the two small buttons on the left side, Mode and Meter buttons.
Loosen the LCD by removing the 3 screws around it.
Solder off the black and the red wire for the backlight. Don't solder off the wires at the LCD but on the flexboard instead. The LCD can be lifted away. Be carefull with the flexiprint underneath, it is fragile. The LCD panel can be held away with a piece of tape. Se picture below.
The circuit board comes with wires soldered on. Different coloured wires are used. Do not connect the wires to other placed than indicated, even if it can be tempting. The operation cannot be assured without the correct connections.
Peel of the covering tape on the backside of the board, and fasten it to the flexiprint on the left side of the prism as shown below.
Connect the wires as the pictures below show. Cut the wires to the correct length. It's better to have the wire 1cm to long than to short. Remember that the top cover is supposed to fit after this is done, so take care when the wires are routed. Be carefull when soldering on the camera CPU under the LCD, the pins are close and a short curcuit here can damage the CPU when the battery is installed again.
The wire colour are as follows:
Black - Ground.
Red - +5V.
Orange - Mirror switch. On main CPU, pin 19.
Yellow - Mirror magnet test point.
Blue - Exp. Comp. switch. On the rewind side of the camera.
White - Main switch. On the rewind side of the camera.
Purple - Shutter release button, on the front side.
Insert the battery case, and test the modification before putting on the top cover.
If you want the leader out after rewind modfication, this is the time to do it. Solder a bride over the two pads on the left, front side of the prism as shown in the picture below. That's it. This will make the leader stay out of the cannister after a rewind and makes it easier to change film mid-roll. Beware that the leader stops over the shutter curtains, and if the shutter is released before the film is taken out, the shutter may be damaged.
Take out the battery case. Resolder all the wires from the top cover again. Make sure the connections are correct before you put the top back again. Also make sure the two small buttons on the left side is on their places. The rubber disk that covers the screw in the eye piece shutter lever can be glued back with contact cement. The front cover goes on last. The stop down lever must be pushed back and make sure it engages the lever inside before you fasten the cover.
I'll make a small batch of boards wich I'm offering to people that wants MLU capability on their T90. First come is first served. I still have boards for sale.
One board is $40 / 32� / NOK 280,- pluss shipping $3 / 2.40� / NOK 20,-. It comes tested and complete with wires.
If the board doesn't satisfy you, I'll refund your money, minus shipping.
I will not publish the source code at this time, so please don't ask. Also I cannot do the modification for your camera, unless you're living in Norway (due to customs). I only sell the boards.
I accept only PayPal at the moment, use the button below. Or if you come from Norway, send me a email for other payment options.
Do not hesitate to contact me at ketil(at)plenty.no if you have any questions or suggestions.
Links releated to MLU in general:
http://www.photo.net/nature/mlu
http://medfmt.8k.com/third/mlu.html
The board layout or software must not be copied in any way. Copyright: Ketil Johansen
Last update: 2005.06.05