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Modifying the TC-80N3 Intervalometer to disable the auto focus activation function


John Jovic

The TC-80N3 (Timer Remote Controller) activates the autofocus on a camera a short period prior to actually tripping the shutter. It's the same as pressing the shutter release on the camera half way to trigger the AF and metering functions without firing the shutter. The effect of this is that its prevents the camera from displaying the histogram after a shot has been fired where the interval between exposures is fairly short, about 5 seconds or shorter. It is important to be able to see the histogram to keep track of exposures and so that adjustments can be made when needed, especially when doing day/night transitions (sunsets). If you can't see the histogram then you can potentially make exposure errors without being aware of them until it is too late.

The TC-80N3 has a single wire which performs the AF function and this wire can de disconnected to stop the AF function. This AF function also acts as a 'wake up' signal to the camera so this function would cease to exist if this modification is performed.

The modifications described below show how to disconnect the correct wire to disable the TC-80N3 AF function. If you do choose to try this then do so at your own risk.
Open the TC-80N3, removing the 3 small screws on the back, then carefully wedge the plastic cover apart using a flat screw driver. It's easy to open and close up again but be careful to note the orientation of the battery so that it can be fitted correctly.  



The cable connecting the camera to the TC-80N3 intervalometer is a simple 3 wire cable which is soldered to the printed circuit board (PCB).  

The red wire is the shutter release, the white wire is the focus activation trigger and the black wire is the shield or earth.


Cut or desolder the white wire. If cutting then be very careful that you don't leave small fragments of wire on the PCB which could cause a short of some kind. If you intend to reconnect the wire at a later stage then it may be easier to do so if the wire is desoldered instead of cut.  

Cover the cut wire with electrical tape or heat shrink so that it doesn't short on anything. Also take care to position it so it doesn't foul anything.

Re-assemble and test.

The modified TC80-N3 was tested with a 1dsMk2 and a 40D shooting in RAW mode. Both comfortably displayed the histogram when 2 second exposure intervals where used on the intervalometer. The 1dsMk2 briefly flashed up the histogram display at 1 sec intervals initially but not after the buffer started to fill which delayed the histogram too much.

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