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Although the Canon EOS 300D has a
'bulb' function, it does not have a mechanical cable release like a
more traditional SLR camera. Unless you wish to hold your finger on the shutter
button for the duration of your exposure, some type of remote switch is
required for any exposure over 30 seconds. You can purchase a dedicated
Canon cable or
even an infrared release (not particularly suitable unless you operate
it from in front of the camera), however both these are expensive
options. It is quite simple to cheaply make your own that connects by a
serial or parallel connector to your laptop or desktop computer. If you
have some spare cash, you can even buy one ready made from
Hap
Griffin.
The cable release I have made is
operated by computer from software called
DSLRfocus or
ImagesPlus. These
applications allow full exposure control and capture of astronomical (or
other) images. DSLRfocus specifically permits careful focusing of dim objects like
stars. ImagesPlus does the same but is also a complete astronomical
image processing suite. I do own DSLRfocus and have ImagesPlus on order.
Please Note: If
you make this cable, please be certain that you know what you are doing
and that you follow the advice provided
here. I cannot
accept responsibility if you stuff up, so build it at your own risk.
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Components
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The following components should be readily available in larger electronics stores.
They were all purchased locally (Tasmania, Australia) from
JayCar Electronics.
The bracketed values above are the JayCar codes.
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Bicolour (red/green) LED
(ZD0250) |
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4N26 opto-isolator
IC (ZD1928) |
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330 and 470 Ohm 0.25W resistors |
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9-pin female serial plug |
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Backshell case to fit 9-pin plug
(the bigger the better) |
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25 mm stereo (3-way) audio plug
(preferably corner design; PP0103) |
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Small piece of circuit board
(cut to resize) |
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Single core
copper strand wire |
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2 -10 m length of 2-core cable (I used
4-core to obtain about the correct thickness) |
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Circuit Diagram |
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My design follows that of Wade
Calvert. You can find the straight-forward schematic
here (at the bottom of the page). The schematic below is a variant
of Wade's that positions the components relative to their placement in
my design. |
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Explanatory pictures |
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Here's the circuit
encased in a standard serial backshell case.
Some intricate soldering was required to enable the fit. The 6-pin
IC was attached to the circuit board on its side with the unused pins 3
and 6 clipped. Pins 1 and 2 were thinned using an emery board, so they
would fit in to the holes on the circuit board. |
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Here you can see the LED raised
sufficiently off the board to allow the very top to just protrude
through the top side of the case (see two pictures down). |
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This is the underside of the
circuit board. The blob of solder at '4 o'clock' is the ground, with no
fewer than 4 connections to it. |
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Here is the completed enclosed case
with the protruding LED. In passive mode the LED is Red. When taking an
exposure, the LED turns green. If you want it the other way around,
simply reverse the LED connections. |
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The other end of the cable is
connected to a 2.5mm stereo audio plug. The 90 degree (corner type) is
preferable to allow easy rotation around the central
shaft. |
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The finished product |
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The finished product!
And it works very well. |
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All information and images are copyright
© 2003-2004 by P B Langsford. Please ask if you wish to use them or link
to them |
