Object: NGC 7635 (Caldwell 11)
Type: Emission Nebula
Distance: 7100 light years
Constellation: Cassiopeia
Date: 6 December 2008
Equipment: SXV-H9, Vixen VC200L (f.l. 1800mm)
Subframes: 22 x 120 second 2x2 binned subframes in H alpha, 16 darks, 16 flats/flat darks, calibrated and stacked in AIP4Win. Final processing in AstroArt and PSP7.
The final image above was salvaged from a catalogue of mini-disasters on a freezing cold and unbelievably soggy Saturday evening.
My first mistake was to attempt to get my SXV-H9 autoguider going. Having found my target and identified a guide star, I spent a frustrating 45 minutes or so trying to get the autoguider to talk to the Skysensor.
First of all, I had forgotten to select the "autoguide" command in the SXV-H9 "default" menu (a step the instruction guide neglects to tell you to do). When I still couldn't get the computer to drive the scope, I tried swapping the cable connection between the "autoguide" socket on the Skysenor and the SXV-H9 (the Skysensor uses a "crossed" signal cable and it's therefore possible - so I thought - to get the cable the wrong way around). To get the guide cable out of the back of the SXV-H9, I had to pull out the signal cable from the autoguider camera to give myself room. When I plugged it back in, I got a white screen on the autoguider image read-out, which I eventually overcame only by rebooting the computer.
I then found that the scope now responded in three directions to guide commands, but not all four, at which point I gave up in disgust. The "crossed" cable was a home build job and I guess I must have missed a wire somewhere.
Meanwhile, clear skies belied the amount of dew that was collecting on every available surface. The VC200L is an open tube scope but I had never had trouble with it dewing up until then. The couple of hours I had spent fannying around with the autoguider had nevertheless allowed dew to completely fog both primary and secondary mirrors.
Ten minutes with a hair-dryer hastily borrowed from the wife's dressing table sorted that out, but by torchlight (an unfair test I know), dried-out clumps of dust were now glued firmly to the previously unsullied surface of the primary mirror, making it look like the surface of the moon.
Having now wasted a couple of hours, I decided to go for 2 minute subframes (I had wanted 5 minute subs, way out of even the GP-DX's capabilities at an 1800mm focal length), which the PEC seemed to allow without significant trailing. I set the camera running to acquire 30 subs, knowing I would probably lose a few to wind or vibration, and that I would have to return to reverse the scope as Cassiopeia would be crossing the zenith, although the GP-DX mount is pretty generous in that respect
When I returned after an hour, the scope was just starting to dew up again. Another blast with the hair-dryer sorted that, and I then spent another 30 minutes reframing the nebula in the field. I decided to put a heating tape around the end of the scope, to try and avoid dewing up. By now, it was bitterly cold, damp and frosty. I set the scope up to gather another 70 subs, and sloped off indoors.
I returned two hours later to find that I hadn't switched the heating tape on, and that I had a scope full of ice and water. Arrrrgh!
Out of 100 frames, only 22 were usable in the end, and I definitely think the dew and dust combination had robbed the stars of their sharpness in those images that were free from trailing or not totally fuzzed by dew later on.
Anyway, the final image, although noisy through lack of subs, shows the full extent of the gas bubble blown from the young blue giant parent, as well as some of the outlying clouds of nebulosity. North is roughly in the 10.00 position.
I now have a scope to clean and a wire to fix. I don't intend to let either beat me, and I WILL get that damned autoguider going...
The final image above was salvaged from a catalogue of mini-disasters on a freezing cold and unbelievably soggy Saturday evening.
My first mistake was to attempt to get my SXV-H9 autoguider going. Having found my target and identified a guide star, I spent a frustrating 45 minutes or so trying to get the autoguider to talk to the Skysensor.
First of all, I had forgotten to select the "autoguide" command in the SXV-H9 "default" menu (a step the instruction guide neglects to tell you to do). When I still couldn't get the computer to drive the scope, I tried swapping the cable connection between the "autoguide" socket on the Skysenor and the SXV-H9 (the Skysensor uses a "crossed" signal cable and it's therefore possible - so I thought - to get the cable the wrong way around). To get the guide cable out of the back of the SXV-H9, I had to pull out the signal cable from the autoguider camera to give myself room. When I plugged it back in, I got a white screen on the autoguider image read-out, which I eventually overcame only by rebooting the computer.
I then found that the scope now responded in three directions to guide commands, but not all four, at which point I gave up in disgust. The "crossed" cable was a home build job and I guess I must have missed a wire somewhere.
Meanwhile, clear skies belied the amount of dew that was collecting on every available surface. The VC200L is an open tube scope but I had never had trouble with it dewing up until then. The couple of hours I had spent fannying around with the autoguider had nevertheless allowed dew to completely fog both primary and secondary mirrors.
Ten minutes with a hair-dryer hastily borrowed from the wife's dressing table sorted that out, but by torchlight (an unfair test I know), dried-out clumps of dust were now glued firmly to the previously unsullied surface of the primary mirror, making it look like the surface of the moon.
Having now wasted a couple of hours, I decided to go for 2 minute subframes (I had wanted 5 minute subs, way out of even the GP-DX's capabilities at an 1800mm focal length), which the PEC seemed to allow without significant trailing. I set the camera running to acquire 30 subs, knowing I would probably lose a few to wind or vibration, and that I would have to return to reverse the scope as Cassiopeia would be crossing the zenith, although the GP-DX mount is pretty generous in that respect
When I returned after an hour, the scope was just starting to dew up again. Another blast with the hair-dryer sorted that, and I then spent another 30 minutes reframing the nebula in the field. I decided to put a heating tape around the end of the scope, to try and avoid dewing up. By now, it was bitterly cold, damp and frosty. I set the scope up to gather another 70 subs, and sloped off indoors.
I returned two hours later to find that I hadn't switched the heating tape on, and that I had a scope full of ice and water. Arrrrgh!
Out of 100 frames, only 22 were usable in the end, and I definitely think the dew and dust combination had robbed the stars of their sharpness in those images that were free from trailing or not totally fuzzed by dew later on.
Anyway, the final image, although noisy through lack of subs, shows the full extent of the gas bubble blown from the young blue giant parent, as well as some of the outlying clouds of nebulosity. North is roughly in the 10.00 position.
I now have a scope to clean and a wire to fix. I don't intend to let either beat me, and I WILL get that damned autoguider going...
3 comments:
A great write up of your trials and tribulations as an astrophotographer, I recognise all the problems.
I take it like me, you don't have a fixed observatory?
What do you do when the scopes are completely covered in frost and ice, how do you get them safely back to room temp? I hate to leave them outside incase they go for walkabout.
Dave:
Thanks for stopping by. I use a mobile platform as described here. When done, I wheel the whole set-up with scope back into my garage - any dew dries out overnight.
Amazing DSLR pictures on your blog (now blogrolled) by the way. I really must get my autoguiding working.
Thanks for that link to your set up, you've obviously thought about all the problems and sorted them.
Auto guiding is the way to go, I can throughly recommend it, I was wary at first after reading about all the problems other people appeared to be having. I managed it first time, a good 10 minutes sub as a test shot.
At the present time I'm in the process of fixing a permanent pier in place, then the mount will be left in situ, I'll just have to attach the scopes.
I've also reciprocated with a link to Suburban Skies.
Regards
Dave
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