Telescope:
My first and only telescope so far is a Vixen AX103S 103mm diameter refractor telescope with a focal ratio of f/8.0 and a focal length of 825mm.
It’s a beautifully made telescope manufactured in Japan, probably more suited to visual astronomy.
By today’s astrophotography standards it’s considered quite a slow scope at f/8.0, which means relatively long exposures.
Its 4in diameter is governed by the cost of manufacturing the primary lens. A 6in telescope would be better, but the cost prohibitively expensive.
The refractor telescope is of the same design as the original Galileo version, and is well suited for a beginner like me, being less demanding on the mount and without the problems associated with some Schmidt–Cassegrain designs.
Its field of view is well suited to targets such as deep space objects or nebulae. It would not be suitable for planets though as they would just show up as stars.
Mounts:
My first telescope mounting or mount was a Skywatcher AZ-EQ6 GT. Probably one of the best entry level mounts.
For astrophotography it’s used as an equatorial mount which tracks objects in an arc using the movement of a single axis (RA or ‘right ascension’ in this case). This means the mount has to be aligned accurately on the Pole Star and the telescope should be perfectly balanced on its mount.
Although it uses belt drives from its stepper motors, it does use worm gears as well.
Mass-produced gears however good will have backlash and I found I was rejecting a number of images because the mount appeared to jump very slightly during the exposure.
RA is not so much of a problem as to track stars the RA motor is always engaged.
The other axes (DEC or declination) can wander back and forth, so backlash is a problem. Some suggest that the telescope should be slightly out of balance to help, but this out of balance needs to be different depending upon which side of the meridian you are imaging.
I also found polar alignment difficult as again the bolts used in the adjustment also had backlash.
At the start of 2016, I sold my AZ-EQ6 GT and purchased an Avalon Instruments Fast Reverse Linear mount. This is what I would describe as a mid-range mount.
It’s manufactured in Italy by Dal Sasso Srl, a small company located near Rome noted for its high precision engineering.
It’s a beautifully made mount CNC machined from a single blocks of aluminium in a bright red anodised coasting and just oozes quality.
Its big advantage over my AZ-EQ6 GT is that it uses belt driven stepper motors, so no backlash along with multiple large conical roller bearings.
It has a 20Kg imaging capacity, so my Vixen at nearly 5Kg is not going to tax it.
With its belt drives, I believe it’s unfortunately susceptible to wind, and generally I don’t image if the wind gusts are greater than about 10mph.
Cameras:
Canon 5D MkII & QSI 683.
I naively assumed my 5D MkII would also handle astrophotography. In some cases this is true such as imaging the moon or sun or some galaxies.
The shortcomings of my 5D for deep space astrophotography were as follows:
- There is an infra-red blocking filter in front of the sensor to enable correct white balance when images in daylight. Some information emitted by deep space objects are in the infra-red, so this information can be lost unless this filter is removed (not for the faint-hearted).
- The sensor is not cooled, and is not suited to very long exposures such as 30mins. The sensor heats up and as it’s sensitive to infra-red this will appear as noise in any final image.
- Any battery would be quickly exhausted, so one needed a mains adapter, but I also found the camera often switched off due to inactivity.
Specialist astrophotography CCD cameras have none of the above shortcomings.
After much deliberation I chose a QSI 683 mono CCD camera. QSI based in America have an excellent reputation for solidly built units and, in this case had a built-in filter wheel.
With my DSLR I got used to the full-sized 36 x 24mm (35mm film) sensor with its 21.1 mega-pixels. Astrophotography CCD sensors are much smaller!
The QSI 683 uses a 8.3 mega-pixel Kodak sensor, with a size of 17.96mm x 13.52mm. This gives me a good field of view with my telescope.
I cool the sensor down to -25 °C, and regularly take 20min exposures with narrow-band filters.
QHY5L-II & Lodestar X2.
My first guide camera was the QHY5L-II but this proved unreliable, and frequently disconnected during imaging runs.
I replaced it with the Lodestar X2, and this has worked out very well.
Filters:
As my main CCD camera is mono, I use Astronomik wide-band filters such as red, green & blue to produce a final full colour image.
The advantage of a mono CCD is that one can also use narrow-band filters which help combat light polution.
The two narrow-band filters I have so far, is an Astrodon 5nm Hydrogen-α (Ha) filter and a 3nm Oxygen-3 (Oiii) filter.
I will add a 3nm Sulphur-2 (Sii) filter probably sometime in the future.
Wide-band filters such as red, green & blue are used to make up full colour images, and narrow-band filters such as Hydrogen-α (Ha), Oxygen-3 (Oiii) and Sulphur-2 (Sii) make up false-colour images such as those imaged by the Hubble Space telescope.
Many of my narrow-band images to date are just in Ha, so they appear black & white.
Remaining Hardware:
NUC.
In my observatory I have a Next Unit of Computing (NUC) from Intel which is a small-form-factor PC (originally running Windows 7 but now Windows 10) and other astrophotography software.
It's a 64bit PC, with a Core i3 processor, 128GB SSD, and 8GB memory, and is connected to the house via an Ethernet cable.
I initially tried multiple USB active extension leads but they proved unreliable.
IP Switch.
My remote IP power switch controls up to 4 devices independently over my Ethernet network using a web browser.
Although not essential, it's useful to be able to switch on/off devices from within the house.
Dew Heaters.
Dew can form on the lens of the main & guide scopes, so by warming them slightly the glass surfaces can be kept clear. I made my own controller, powered from a mains 12v power supply.
This power supply will also power my flats box when it is completed.
Lodestar X2 guide camera & Altair Maxiguider 80 guide scope.
As good as my mount is at tracking stars, there are techniques to improve the tracking even further.
The guide camera coupled to the guide scope, locks onto a nearby guide star and software then makes tiny tracking corrections.
Lakeside Motorised Focuser.
There is no built-in auto-focussing in astrophotography, so I use a stepper motor attached to the main telescope and software to determine the best focus point.
PoleMaster.
Good polar alignment is essential, and the PoleMaster makes use of a super sensitive wide field imaging camera which detects Polaris and the dimmer stars surrounding it. From the positions of these stars PoleMaster can determine the position of the true pole compared to the mechanical axis of the mount and allow one to make adjustments to bring them into line.
