My Deep Sky Astrophotography Setup
My imaging setup consists of 2 telescopes mounted side by side on an EQ6 equatorial mount, the primary imaging telescope is a skywatcher 200mm newtonian, and the secondary telescope is an Orion ED 80mm refractor which I use as a guide scope
For my primary imaging camera I use a Canon 300D digital SLR which I have modified by changing the internal infra-red blocking filter for a 'Baader' conversion filter, as the standard filter in the camera has poor transmission in the red hydrogen wavelength, many deep-sky objects, such as nebula emit light in this hydrogen-alpha wavelength, so the replacement filter allows better transition of the light and makes the camera more sensitive for recording images of deep sky objects
I followed the instructions at Gary Honis' website to carry out this somewhat delicate procedure, and after some advice from Andy Ellis, when it was re assembled I was pleased that it still worked! Professional modifications to cameras can be done by Andy Ellis from Astronomiser
The camera is mounted onto the telescope by removing the lens and fitting a 2 inch 'nosepiece' which slides into the telescopes focus drawtube
Once the camera is attached, I conect a 12v power supply via an adapter instead of using the battery, and also the USB and remote shutter cables to control the camera from the computer. Localised light polution from streetlights is filtered out using a clip-in CLS filter which blocks out the sodium wavelength
My guide camera is a Philips Toucam Pro II CCD webcam, which has been modified for long exposure imaging to the SC1 modification, again by Astronomiser, and re-housed in a small plastic case, again here the standard lens is removed and a nosepeice attached to allow conection with the guide telescope, and a USB cable to conect to the computer
A flip-mirror is also used so that I can look through the telescope to find and focus on a star, before fliping the mirror to the camera. I also use a small 50mm finder scope to find my targets and centre the objects in the cameras
Once all the cameras have been set-up on the telescopes, I connect them and the mount to a 'hub' which is mounted on the telescope pier. The hub is basically a box which contains a 230v to 12v DC 5A supply, and a PWM (pulse width modulator). The box has outputs to power the mount and cameras, and also outputs for dew control heaters mounted on the telescopes to prevent condesation and ice forming on the optics, a 4 way powered USB hub and a USB/Serial adapter is also mounted on the box where the cameras all conect into.
This is then connected directly to the PC where software is used to control the GOTO functions of the mount, the DSLR exposure settings and also the guiding software through the ASCOM astronomy communications protocol and EQMOD mount control software. This allows me to use the planetarium program Starry Night to select and goto over 16 million stars and 1 million deep-sky objects in the sky by selecting it from the sky atlas
Once everything is connected, I slew the mount to a bright star to check alignment and to focus the cameras, the guidecam is focussed by eye using the flip mirror and a 20mm eyepiece which has been parfocalised with the camera, and a home made Bahtinov mask is used to focus the primary imaging camera. Trying to focus by looking through the camera is a bit hit and miss, and as focus is critical to deep sky imaging, time spent getting it perfect is essential. The Bahtinov mask helps this process and provides an easy way to ensure the focus is correct, it is simply placed over the front of the telescope and the slots in the mask create a diffraction pattern of the the star, when the image is downloaded to the PC I then make small adjustments to the focusing until the difration pattern becomes symetrical, this indicates exact focus.
Once focus is achieved, the mask is removed and the focus point locked to prevent accidental movement.
Now focus is setup, I can slew the mount to my chosen target, and by taking short 30 second exposures on the highest ISO I use the images to adjust the mount and camera orientation to get the desired image composition, then using the PHD guiding software I select a single star from the guidecam live-video image and run a calibration routine, this moves the mount in all four directions and reads which way the star moves and saves the parameters to be used when guiding. When callibration has finished, the software will monitor the guide star and send signals to the mount to adjust for any slight movements of the guide star caused by minor innacuracies in the mounts mechanics, the result is zero tracking errors which then allows for extended exposures with the DSLR camera
The only thing remaining to do now is set up the DSLR camera to take a series of exposures, depending on the target, exposures usually range between 3 and 5 minutes at 800 ISO, this is done with either APT or DSLR Focus, both of which are excellent tools for DSLR control, in the interface you choose your exposure and ISO settings and the quantity you want, and start the routine running
Once I am happy that everything is working correctly, I can go and put my feet up for an hour or so whilst the images get taken, always keeping half an eye open for any passing cloud
