New telescope - 254mm Newtonian
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In August 2009 I obtained a Sky Watcher Newtonian reflecting telescope, 254mm (10 inch) aperture, f/4.8 (so the focal length is 254 x 4.8 = 1,219mm).
It mounted on my existing HEQ5 equatorial mount with just one small snag: I needed a longer rod for the counter-balance weights to avoid having to put excessive weights on. The telescope weighs about 15kg and I needed 25kg to balance it with my EOS camera on it; as a temporary measure I visited a sports shop for extra weights. Longer rods are available and I have now received one. It enables me to use only 10kg of balance weights, putting less strain on the mount.
Another slight snag at first was that it was not immediately obvious how to attach my SLR camera (Canon EOS 5D MkII). The focal plane of the telescope, after reflection from the secondary mirror, is quite close to the tube. That is fine for focussing eyepieces but the camera body needs about 50mm more distance. The telescope was advertised as having a direct SLR connection but there was no documentation explaining what was intended. I eventually noticed that the 2x Barlow lens included with the instrument has a screw thread at its exit end. A little experimenting showed that my Canon fitting T-mount, that I already had for my Meade ETX, would screw onto the Barlow lens. So that must be the intended method of camera attachment. The method is called negative projection (see, eg, Covington's book, "Astrophotography for the amateur"). It makes the effective focal length somewhat larger (by about 2 times) and the f-ratio correspondingly smaller. Never mind, the f-ratio is less significant in astro- than in ordinary photography; what matters is the light gathering capability of a decent sized primary mirror. My first images with this set-up showed that I can photograph stars down to magnitude 16.5 even from my light-polluted suburban site.
Here is a picture of the new scope:
Telescope documentation
No manual of any kind was provided with either my HEQ5 mount or my SkyWatcher telescope. I think that is appalling considering their cost. A Google search found a manual at http://www.skywatchertelescope.net/swtsupport/Instruction_Manuals/HEQ5andEQ6130405V1.pdf but that still lacks a lot of important detail. I have therefore written a page about my own discoveries of how to use the various parts of the telescope, linked here
New observatory
Well, it's just a good sized shed that stores all the equipment and has room for me to sit at a table when photographing from my PC. I considered making a sliding roof and mounting the telescope permanently inside but decided that making it properly waterproof and yet light enough for easy sliding, at the size that would be needed for access all around the telescope, was not practical. So instead I have concentrated on making it quick and easy to set up the telescope.
The shed is beside a paved area in the corner of the garden, so it is sheltered by 6ft high fences. Being paved it provides a solid base for the telescope mounting. The mounting is a tripod so I have drilled 3 holes in the paving for the tripod feet to sit in. Smaller holes in the base of those holes go right through the paving so that rainwater drains away. I have painted round the holes so I can find them easily in the dark.
So the tripod is easily erected in exactly the same spot every time. Or at least, exactly enough for the kind of photography I am doing, where GRIP software takes care of small drift. Therefore I have aligned the tripod on the celestial north pole just once and do not need to do that every time I set up.
The plastic water pipes in this photo carry cables from the shed to the telescope. I have used water pipes because the diameter is a bit bigger than normal DIY trunking for electric cables. The two sections of pipe make it very easy to simply fold the assembly up inside the door of the shed when not in use. A couple of hose clips and a strip of red velcro enable one of the pipes to be attached to the top of a tripod leg quite firmly but in a way that is easy to detach again.
There are 4 cables through the pipes:
- 12v DC power supply for the stepper motors in the HEQ5 mount, a cable I made myself. Inside the shed is a mains power supply to which this cable is connected.
- 7.2v DC power supply for the Canon EOS camera, enabling Canon's power supply to be inside the shed too. I had to cut Canon's cable and insert connectors to make my own extender cable. The alternative would be to carry mains out to the tripod but I did not like that idea.
- RJ11 extender cable so that I can sometimes use the hand controller for the HEQ5 motors from inside the shed. I checked that only 4 wires of the 6 possible in RJ11 plugs are connected inside the hand controller. That enabled me to buy a standard RJ11 extender cable.
- Active USB extender cable (bought) so that I can sometimes control the Canon EOS camera from my PC inside the shed. Canon provides free software with the camera for remote capture via USB.
A fifth cable may be added if I can find a focussing motor that will fit my telescope. I will then be able to focus from sitting at my PC as well as drive the telescope around and take photos.
Everything in the shed is connected more or less permanently but it is all easily unpluggable when I want to transport the telescope elsewhere.
Here is a close-up of the cables at the tripod end. The helical plastic enables enough cabling to hang out of the end of the pipe so that the tripod head can move to all positions without fouling or straining the cables. It is of course important to check that. The two connectors hanging down are USB and power for the camera. The other two cables are plugged into the mount.
This arrangement is not only very quick to set up and take down but it also considerably reduces the scope for cable entanglement (which can be quite a nuisance in the dark).
First photos through the 10 inch telescope
Clear evening skies are rare this summer (2009) in northern Britain. One occurred on 15th August and I grabbed the chance to start trying to photograph through my new telescope. It was breezy that night. Also I did not attempt to align the polar axis of the mount. For both of those reasons the star images are larger and less circular than I expect they will be under better conditions. Nevertheless I was delighted to find it quite easy to capture some deep sky objects. My observing site is on the edge of the conurbation of Tyneside, so light pollution is significant. I did not use any kind of filter so I was pleased to discover that my first photos show stars down to at least magnitude 16.5 (1/10,000 of the brightness of the faintest stars visible to the naked eye in an unpolluted sky). That demonstrates the light gathering power of a 10 inch diameter mirror, assisted by the very high ISO sensitivity settings possible in the EOS 5D MkII. As usual I took many photos of each object and combined them in GRIP to reduce noise.
So, the following snaps are far from perfect but to me they represent a very encouraging start.
M13 globular cluster in Hercules
M92 globular cluster in Hercules
Jupiter and its Galilean satellites
Canon EOS5DMkII 254mm Newtonian @ 2380mm 0.5s f/9.4 ISO1600 2009:8:15 23:31:40
Not a good photo but similar to what Galileo would have seen. Jupiter is currently very low in the sky from here. From left to right the 4 satellites are II Europa, I Io, III Ganymede, IV Callisto.
Core of M31 galaxy in Andromeda
Canon EOS5DMkII 254mm Newtonian @ 2380mm 24 x 10s f/9.4 ISO12800 2009:8:15 23:20:52-23:26:42
Again I am sure I will be able to do better, but this is just the first session with the new scope. As explained above, the field of view in my camera is 50' x 33', so only the central core of the Andromeda galaxy is captured here. You can see the bands of gas obscuring some of the stars in the galaxy but the individual stars are not resolved.
A later and better photo can be seen here.