ATTACHING THE DIGITAL SLR TO THE TELESCOPE
Once the telescope alignments are complete, I then slew to the target that I want to image. At this point, the telescope reticule eyepiece is still inserted from the alignment process. If the object is bright enough, I will center the object in the field of view if necessary. Otherwise, I do this later with short exposures and hand controller adjustments. More on this in a bit. Once the telescope is pointed at the target, it is time to remove the eyepiece and insert the camera.
Connecting the digital SLR to the telescope requires a T-ring and T-adapter as shown below. The following steps show how to attach the DSLR to the telescope.
Step 1: T-adapter and T-ring are separate components. Note that the T-ring must be specific to the type of digital SLR used.
Step 2: The T-adapter and T-ring are threaded. The two components are combined.
Step 3: Attach to digital SLR. The T-adapter/T-ring assembly inserts into the DSLR just like the camera lenses do.
Step 4: Attach digital SLR to telescope. The DSLR with T-adapter/T-ring assembly is inserted into the telescope eyepiece holder directly (i.e., no eyepieces, Barlows, etc are used). This is considered “prime focus” astrophotography. The telescope optical tube serves as the camera lens.
Important tips: tighten the telescope thumbscrew to the T-adapter securely. Also, be sure to attach some type of DSLR strap to the telescope in case the camera falls.
DIGITAL SLR COMPUTER CONNECTION
One thing really nice about my Canon XSi is that I do not need a special shutter control cable like I did with the Canon Digital Rebel (300D). The XSi uses a standard USB cable that works in conjunction with the EOS Utility that came with the camera. I actually have a remote connection to the XSi and telescope using buried Cat. 5e cable that runs in Schedule 40 conduit from my telescope to control room in my garage. On both ends I use simple USB to Ethernet adapters. If there is enough interest, I can document this remote setup. Just leave a comment in the “Leave a Reply” section at the end of the tutorial. Not to worry, my tutorial works the same if you are using a laptop at the telescope. My remote setup is nothing more than extensions of the USB cables. Most of my work is done indoors where it is comfortable!
At this point, the telescope is pointed at the object that I want to image and the DSLR is inserted in the telescope. With the USB cable already connected to the computer and XSi running on AC power (with optional adapter), I turn on the camera. The camera mode dial should be set to manual as shown below:
If everything is connected correctly, an autoplay pop-up will appear on the computer screen:
Just cancel this pop-up by clicking the red “X” in the upper right corner. Open the EOS Utility that came with the DSLR.
EOS UTILITY INSTRUCTIONS
1. Upon launching the EOS Utility, the camera control screen will open as shown below. Click on “Camera settings/Remote shooting”.
2. This will bring up the main interface for remote operation of the XSi. Note that it is already set to manual from the mode dial setting earlier. In order to take long exposures, the DSLR must be set to “bulb”. In the screenshot below, it is already set to bulb. By default, it may be on another exposure setting. To change to bulb, simply hover your curser over the icon (where bulb is shown in the screenshot) and right-click (or double-click). Now click on the left double-arrow button and it will go to the bulb setting. Now just move the cursor away.
EOS Utility Settings for DSLR Astrophotography
Do the same for the other settings in this area. The screenshot above depicts the settings I used last time I imaged.
Shooting mode: bulb
White balance: daylight (popular setting)
ISO speed: 1600 (this varies depending on the object)
Metering mode: evaluative metering (which was default)
Image recording quality: RAW (maximum data)
Image save location: computer (images automatically upload to computer after each exposure is complete)
DSLR TEST SHOT
At this point, it is time for a test shot to see how well centered the object is and how much focusing is required. To take a a shot, press the shutter button at the top right hand corner of the EOS Utility interface.
Click the Shutter Button to Start the Exposure
For bright objects, I only take about a 1 minute exposure but perhaps 2 minutes or more for faint objects. The shot duration will be displayed in the window to the left of the shutter button. Be sure to click the shutter button again once the desired amount of time has elapsed. This will stop the exposure and the image will automatically transfer to your computer and will display in the quick preview window.
After the object is centered, I will start the focusing process. Note that many times I will actually focus while I’m centering the object since it minimizes the number of trips to the telescope (remember I’m imaging remotely). For focusing, I use the popular Bahtinov focusing mask. This thing makes focusing very simple and quick! The mask just lays over the end of the telescope tube. Then I take trial shots with the digital SLR and adjust focus until the diffraction spike pattern is symmetrical. The video below demonstrates this process on a SCT rather than the ED80 that I use. It is the same process though. Note that many times I further fine-tune the focus after my autoguider is going (discussed in the next section). This makes for a cleaner image for determining the symmetry of the diffraction spikes. Make sure that you remove the Bahtinov mask when the focusing process is complete!