When
we started this site one of our first pages concerned the
conversion of the Pentax cable 'F' switch - used with the 'Z'
series film cameras - to enable it to be used with the
*ist-D. Cable 'F' switch .
(This can also be used when converted with the same cameras that
this DIY electronic cable release is intended to be used with).
Since that time there have been
several users who have made their own electronic cable releases
and recently there has been renewed interest in this subject.
In
order to assist those who would like to try this we are providing
some details on how to go about this and the parts that you will
need. Making your own electronic cable release is fairly easy and
cheap. It cost us just £5.00 to buy the parts needed, a fifth of
the cost of the cheapest electronic cable release that uses the
same connection.
The
electronic connection used in the camera's is a 2.5mm stereo
audio socket. Many DSLR's/SLR's from several makers now use this
connection for use with electronic cable releases. Plugs to suit
this connection, usually called stereo jacks, are easily obtained
from any good electronic store, as are most other parts needed. In
the UK www.maplin.co.uk
is a good online source. They have also recently started to open
stores on a number of high streets, conveniently replacing the
Tandy electronic shops, a past good source of components, who
disappeared a few years ago.
As
there many camera users who are uncertain about how the electronic
cable releases work, and thus what parts are required, and why,
we will deal with this aspect first.
Camera
Shutter Buttons
Camera
shutter releases - shutter buttons - work in two stages. The first
stage, the half-press, engages the AF and metering circuits. The
second stage, the full press, also engages the shutter circuit.
The switches used are of the pressure type. Applying pressure
makes/completes the circuit, removing it breaks it. These are
signal circuits. What this means is that the circuit does not
carry much current, just that when made it 'switches on' further
circuits. In these cases the AF/metering and shutter circuits.
Electronic
cable releases are designed to work in the same way, again using
two stage pressure switches. In order to make them easy to
use with the bulb mode, especially with long timed exposures where
it can become awkward continuously holding down the shutter
button, some cable releases have a 'lock' which when used keeps
the switch 'on' and the shutter open. In bulb mode of course the
shutter remains open for as long as the shutter button is pressed
down.
Two
stage switches are used to ensure the AF/metering circuits engage
before the shutter circuit. This is for two reasons. It enables
the AF system and metering to be used without actually taking a
shot, the button only being pressed half way and no further. And
it prevents the shutter being fired without the lens being
correctly focused if this is desired. Whilst the shutter
will fire if the circuit is energized, the circuits are designed
so that once the AF circuit is made, the shutter circuit will not
complete and the shutter fire until the AF system has worked and
confirmed correct focus. This only occurs in single shot or
continuous AF. When the camera is set to MF mode, whilst a half
press of the shutter button will engage focus confirmation and
metering, it will not prevent the shutter firing on full
depression of the shutter button, which occurs irrespective of
whether correct focus has been obtained and confirmed.
In
single shot AF once the shutter button as been pressed halfway and
the circuit made the AF works until focus is confirmed. It does
not matter if the circuit remains made the AF will not continue to
work. The circuit needs to be broken and re-made for this to
happen. This happens by lifting your finger from the shutter
button and then pressing down again. In continuous AF the opposite
happens. The AF works and continues to work, re-focusing as
necessary, until the circuit is broken.
When
the shutter button is pressed fully down and the shutter circuit
is made the shutter fires. For how long it remains open depends on
the metering mode used. In every mode except 'bulb' the time is
fixed by the metering method being used and the shutter will close
after this time. In 'bulb' mode the shutter remains open for as
long as the shutter button remains pressed down. How many times
the shutter fires depends on the AF mode chosen, one in single
shot and multiple in continuous.
As
you can see, shutter buttons using pressure switches are used
because they provide the most convenient way of making the
AF/metering work and firing the shutter. The only slight drawback
with the design is, as we have stated, the awkwardness of holding
down the shutter button for long periods in connection with long
time exposures in bulb mode. But this is over-ridden by the fact
that in general very few photographers use bulb mode much these
days, and some not at all. This is particularly true of present
day cameras where timed exposures of up to 30 seconds are common
and cater for most needs.
Wiring
circuits
The
circuits for wiring a cable release are simple on/off one's, most
of the circuitry being inside the camera. Just three core cable is
needed. One core carries the 'feed' from the camera to the
switches, with the other two carrying the feed back when the
contacts are made completing each respective circuit. fig 1
Although
we have tried, we have been unable to find any proprietary two
stage pressure switches that could be used as a shutter button,
and so two individual push button pressure switches need to be
used. These are very common and easily obtained. As a result all
you really need to make a cable release are two push button
switches, a container which fits in the hand in which to fit them,
a length of three core cable, and a 2.5mm stereo audio jack.
Finding
a container in which to fit the switches, and which is easy to
hold and obtain has been cleverly solved by those who have hit
upon the idea of using an old film canister/container. Small
diameter 3 core cable is not so easy to find. We have used some
3amp, but it's diameter is still a bit too big and the cable is
rather stiffer than we would have liked, but it does the job. You
may have better luck in finding more flexible smaller diameter
cable.
An
additional switch you may like to incorporate into the design is a
simple on/off type to use with the bulb mode. This is wired in
parallel with the shutter circuit push button and used instead of
it when needed. fig 2
Here
are shots of the switches used along with the stereo jack.
The
wiring for the stereo jack is as follows ; Base - feed. Middle -
AF/Metering. End - Shutter. Be sure to use a simple on/off type
toggle switch if you fit one for the bulb mode. These toggle
switches are made in a variety of formats which outwardly look
similar, single pole, double pole, on/off, changeover, centre off,
passing contact. Just ask for a single pole on/off type.
Actually
making the cable release is not a difficult or time consuming
business and is easily accomplished with a small soldering iron of
about 15watts with a small tip and something with which to make
the holes in the film canister for the switches and the wire.
We
played around with the film canister for a while whilst deciding
where to position the push buttons and came to the conclusion that
for us, placing the AF button in the middle top, and the shutter
button about half way down the side worked well. It seemed easier
to push down with your thumb, and then squeeze with your index
finger, rather than the other way around. But of course where you
place the buttons is up to you. Some place both buttons on
the side. As two individual buttons are used you must remember
that the design requires that you are able to depress the
AF/metering button before the shutter one. All you must remember
to do is to leave enough room between them inside the canister so
that their respective contacts do not touch.
It
is best to actually wire up the two push button switches before
fixing them in place in the canister. It's impossible to
solder up the connections once they are fitted in the canister.
Similarly it's best if you can find some way of holding the stereo
jack while you are soldering up the wires to it. We used one of
those 'helping hands' units that has crocodile clips for holding
objects while you work on them. See photo's below.
And
here is the finished result next to the standard Pentax cable 'F'
switch. As you can see there is hardly any difference in size and
it works just as well.
Not
bad for a fiver [£5.00], a little effort finding the parts, and
an hours work making it.
