Nikon D40/D70s/D80 MaxIm DL/MaxDSLR long exposure (bulb) cable
MaxIm DL and MaxDSLR are astronomy programs by Diffraction Limited. They provide connection between DSLR cameras and telescope.
To control exposures longer than 30s with Nikon DSLR you have to use long exposure (bulb) cable connected to PC.
Diffraction Limited provides schematics for long exposure cable connection with Canon DSLR in help file of MaxIm DL/MaxDSLR. None is provided for Nikon DSLR. So I decided to build my own cable based on schematics for Canon DSLR.
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Nikon D40/D70s/D80 DSLR’s have a special 4 pin connector for remote shutter release cable (Nikon MC-DC1 cable). Easiest way to get the connector is to buy cheap long exposure cable off Ebay (<10EUR).
First thing you want to do is dismantle remote shutter cable, so that you have only the cable without anything else (Nikon connector on one side, three wires on other side).
Dismantled Nikon remote shutter cable
Nikon remote shutter connector close-up
Then it is REALLY IMPORTANT to correctly identify three wires from the cable that we will use. You have to find out which one is GROUND. DO NOT TRUST ANY MARKINGS ON THE CIRCUIT PROVIDED WITH SHUTTER CABLE YOU BOUGHT!
To do that connect the cable to your DSLR and measure with multimeter which wire (of the three possible) is in short circuit with external flash holder (since this is also grounded).
Now you have found GROUND wire. The two remaining are FOCUS wire and SHUTTER RELEASE wires. For this cable it is not really important which is which, since we will use both on same connection.
But if you would like to know which is which you can do simple test. If you connect FOCUS wire with GROUND wire camera should focus. If you connect all three wires camera should take a picture (do shutter release).
Schematics for MaxIm DL/DSLR (PC RS232) <-> Nikon D40/70s/80 cable:
After you built the cable recheck everything before connecting it to PC/DSLR! You can try it out with DSLR Cable Tester utility provided by Diffraction Limited here.
(c) 2008 ALiEN
I am not responsible for any kind of damage that might occur using provided information.
It is very simple design. With RTS signal on RS232 serial port we switch T1 transistor ON/OFF and thus make connection between NIKON GROUND wire and NIKON FOCUSING/SHUTTER wire.
You can build everything in casing of serial connector: