Although DSLR cameras are very flexible, they were not necessarily designed with astronomy in mind. As such, some preparation is required in configuring your camera and your telescope.
It is extremely important to review the Camera Setup sections below, especially the sections on cables and camera settings. Failure to follow these instructions may result in the software being unable to operate the camera. Also please refer to the instructions for your specific camera model in the Camera and Autoguider Setup section.
Unlike manual film SLR cameras, DSLR cameras require electrical power. Typically this is provided by battery power.
For longer sessions, the battery charge may not be sufficient, especially under cold wintertime conditions. Also many cameras automatically power down if they have not been used for a few minutes. This can result in unexpected disconnection from the computer control. Therefore if running on batteries it is best to turn off the automatic shutoff feature through the camera's built-in menus.
If at all possible the camera should be powered from an AC or DC external power adapter. This will allow for continuous use with no risk of the battery discharging, and for most cameras this will disable the automatic power off feature. An alternative is to use an external battery pack, which are often available as optional accessories.
DSLR cameras come with a USB or FireWire cable, for connecting to the computer. For most users, these cables are only used to download images from the Compact Flash card into the computer. But in most cases, the cables can also be used to control the camera remotely from the computer.
FireWire and USB 2.0 cables provide the fastest data transfer. Downloading
images using the older USB 1.1 connection is much slower
If you do use a USB 2.0 camera, all of the components must be USB 2.0 compatible, including the cable, any USB hubs between the computer and the camera, any extenders, and of course the computer port itself. If any of these items are USB 1.1, the interface will fall back to the slower speed. If you have an older computer that only has USB 1.1, you can purchase PCMCIA or PCI plug-in cards that provide a USB 2.0 interface.
Sometimes it is necessary to trade speed for connection distance. Some people want to operate their camera in their observatory or back yard, from a machine inside the warmth of the house. USB 1.1 extenders can make very long runs and still work reliably. There are also products such as Anywhere/USB and allow TCP/IP connection to USB devices from long distances, but they are limited to USB 1.1 speeds. So if you make the trade-off, do it consciously, and not by accident.
DSLR cameras are designed to work as much as possible just like film cameras. As a result, they have "exposure stops". It is not possible for many camera models to take an exposure longer than 30 seconds; nor is it possible to take an arbitrary exposure time. For example, most cameras will do 4 or 8 seconds, but will not do 5 seconds.
Fortunately all DSLR cameras include a "bulb" setting, originally invented in the days of mechanical film cameras for use with flash bulbs. In bulb mode, the shutter is held open for as long as the shutter button is depressed. Old SLR cameras required a mechanical "bulb cable" to operate the shutter; more modern cameras use electronic cables.
Many newer DSLR models can perform this "bulb" function through the USB or Firewire cable. Older Canon models (prior to 30D) and Nikon models require a separate Bulb cable. In addition, most cameras that support an optional mirror lock-up mode will also require the extra Bulb cable when operating in mirror lock-up mode, even if they do not require it for the Bulb function itself.
In order to facilitate computer control of the shutter, various people have invented ways to construct computer-controlled shutter cables. These shutter cables have become informally standardized, and can be purchased from a variety of sources such as telescope dealers. They can also be assembled by someone with basic soldering skills using about $20 in parts from a local electronics store (see below).
Serial and USB cables are generally much more trouble-free than parallel cables. For most parallel cables, the cable must be plugged in after the camera is connected to the software; otherwise the camera may fire random shots and fail to connect. Also parallel ports are obsolete and newer computers do not have them.
Some cameras have special connectors or infrared (IR) receivers, as follows:
Cameras such as the Canon Rebel series have a simple 2.5 mm female plug on the camera for bulb connection. This is fairly straightforward to interface with.
Cameras such as the Canon EOS (non-Rebel) series have a proprietary, and patented, "N3" connector for the bulb cable. A common approach is to purchase a manual bulb cable and insert a pair of 2.5 mm connectors in the middle. This allows the original bulb gadget to be connected, or a bulb cable to the computer. Some vendors supply prefabricated N3 computer bulb cables.
The Nikon D70 requires a special IR sender on the cable end for long exposure.
MaxIm DL supports the full cable line of Hap’s Astro Cables http://www.hapg.org/astrocables.htm, which are also available through some telescope dealers. Hap Griffin also provides custom modification of cables to suite special needs.
Oceanside Photo and Telescope http://www.optcorp.com/ also supplies computer bulb cables.
A handy DSLR Cable Tester is available on our web site. If you encounter problems operating your bulb cable, please check it first with this handy utility.
If you wish to assemble you own exposure cable you will need to obtain the parts (all available at Tandy/Radio Shack) and have basic soldering skills. This section covers the serial cable portion for the Canon Rebel series.
The following parts are required:
|
Qty |
Part |
|
1 |
Resistor 47k |
|
1 |
Transistor 2N3904 |
|
1 |
Diode 1N4005 |
|
1 |
2.5 mm stereo audio plug |
|
1 |
Two conductor wire |
|
1 |
DB9 female connector |
The circuit schematic diagram is shown below.
Other Canon EOS models (20D, 30D, 40D, etc) have the proprietary N3
connector. To accommodate these cameras, you can modify a standard Canon
remote bulb cable, by breaking the cable and introducing a connector pair
into the middle.
Connector details (top), and the two halves of the modified Bulb cable
(bottom).
The bulb cable's connections are as follows:
|
Connector |
Wire |
Function |
|
Tip |
Red |
Shutter |
|
Center Ring |
White |
Focus |
|
Outer Ring |
Black |
Ground |
To prepare the modified Canon remote bulb cable:
Cut the bulb cable in two at a convenient point somewhere in the middle.
Strip all the wires. Trim to fit and tin each tip.
Unscrew the outer plastic cover on each connector.
The Male connector will go to the controller or the switch side.
The female end will go to the N3 plug side (camera side).
Make sure you thread the cable through the appropriate covers before soldering or you will have to do it all over again!
Solder the red wire to the tip lead, the white wire to the middle lead and the black wire to ground. Make sure that none of the leads or bare wires can touch. Use a small piece of electrical insulation tape to ensure this.
Ensure that the whole joint, cables ends and insulation all fit under the cover. The ground wire should take the tension for the cable so the white and red wires should not have loads on them if the cable is pulled.
Test the cable by checking the focus, then the shutter.
Now test the cable with the computer control.
Since DSLR cameras were originally designed for standalone use, some settings are not controllable from the computer. This is particularly true where there are physical switches that cannot be operated remotely. Camera control will not work if these switches are set incorrectly. In particular:
The camera must be set to Manual or Bulb Mode. Usually this is marked with an "M" on the dial (Bulb mode on the Canon EOS D1mk2). Otherwise the software will not be able to connect to the camera.
For cameras that can set stops in the 1/2 and 1/3 ranges, use the 1/3 setting. (Some cameras with modified firmware require the shutter speed to be set to 1/3 for remote operation.)
If the USB port can be configured for print mode or PC control mode, use the PC control mode.
If a regular lens is attached, set the AF/MF autofocus select switch to MF for manual focus. Otherwise exposures will never complete.
If you wish to remove the Compact Flash memory card from the camera during imaging, be sure to set the mode that allows the camera to operate without the card (most cameras have this option on the menus). The memory card is not necessary during software controlled operation since the images will be downloaded directly and stored on the hard drive.
For Canon EOS cameras, you must install the camera remote control software that is supplied with the camera, since it installs the drivers used to operate the camera. No such software is supplied or is required for Nikon cameras.
Some cameras must be set to PTP mode through the in-camera menus; others must not be set to PTP mode. Please refer to the Equipment Setup section for more information.
In order to make sure that the camera cables and settings are configured correctly, please follow all instructions that came with the camera.
Some camera models have an optional mirror lock-up mode; with almost all camera models you must use a bulb cable even if the camera can take long exposures without the cable.
When focusing DSLR cameras via software, you cannot use the raw images unless they are converted to color or binned. The Bayer color matrix will superimpose a dither pattern on the image, which will make it impossible to measure star diameters.