When you want to see the stars, find someplace dark
After years of a nearly blank solar disk, we have a beautifully active Sun. Any time you have a chance to see the Sun through a telescope this year, do so. The view is replete with sunspots, or if you have a Hα filter, prominences and more…
I have had a problem observing here in Hawai’i. The skies can be gorgeous, there is little to no light pollution, and you have access to much more of the southern sky. What could go wrong? …Dew!
I had one dew strap available, given to me by a friend and fellow observer, a small one just right for wrapping around an eyepiece. So I just needed a controller to get started. There are several of these available on the market. But I had some issue with the cost, it seemed a bit high for what was essentially a very simple device. Some of the commercial units offered features like temperature sensing and regulation. Simple overkill for most users actual needs, just warm the optic slightly until the dew goes away. Sounds like an excuse for another evening project to me… Build it!
Astrophoto gear takes a while to setup. A lot of little bits and pieces are required that make up the mount, the telescopes, and the cameras. This is all connected with cords and cables, a computer, an autoguider, extension cords for power and more. Coming up with a way to minimize the setup is a big advantage. The best solution is to build a personal observatory where the telescope can be setup and remain setup. Since I am not likely to have that solution available any time soon I use the next best thing. I assemble all of the gear and simply roll it out of the garage to use and roll it back when I am done. This reduces the setup time to about 10-15min, in place of almost an hour if done from scratch. The computer and support gear sits on a table small enough to pick up and carry out intact. connect an extension cord for power, connect three cables from the table to the telescope, turn it on and go.
Two telescopes set up on the side of Mauna Kea. Olivier’s 12″ and my 18″ Deep Violet. A full night of deep sky observing under very nice conditions.
The photo was taken with a red LED light swept over the area during the 20 seconds of exposure. The camera had other ideas, set for automatic white balance it attempted to correct the color, fairly successfully. Surprising given the monochromatic nature of the light source.
As usual, click on the image for a larger version…
Yes, it is three in the afternoon and I am just waking up. That was the plan.
A night spent under dark Mauna Kea skies with a telescope. It has been much too long since I had a good night out with the ‘scope, it was time. A few items conspired to make it happen… Good weather, a note from the HR department that I was at maximum on accumulated vacation time, use it or lose it! Additionally, my friend and co-worker, Olivier Martin, was looking for a night of observing as well.
With a couple days of approved vacation I headed for the mountain.
A partly cloudy sky greeted us on arrival, high and heavy cirrus hid much of the blue. The forecast was for this to clear off during the first part of the night, not yet time to panic. Not wanting to deal with the crowd at the Mauna Kea VIS we hid out in a spot I found on one of the nearby back roads, a place where we would not be disturbed by any visitors through the night, a place that is completely dark.
Finally, a night where… A) The sky is clear. B) The wind is not howling through the palm trees. C) I am not exhausted by working the summit. D) I do not have to get up early the next morning.
A + B + C + D = Astrophotography from the driveway!
The comet is nicely placed in Ursa Major, transiting late in the evening, available for several hours of exposures. And expose I did, with the auto-guider locked on the a dim star beside the comet, the shutter open for well over two hours. I was shooting my Canon 20Da and the AT6RC, a combination that framed the comet nicely.
It will take a while to get the resulting images processed. In the meantime I did a quick process on a set of images taken with the wide field/finder CCD camera. The results of which can be seen at the right. I also shot a few quick images of the M95 area with the CCD to capture SN2012aw.
In April 2001 I realized a dream that had been many years in the dreaming and a year in the making, a large aperture dobsonian.
Over a decade of engineering experience has taught me that a well defined set of specifications can make all the difference at the end of a project. With these design goals in mind the plan then progressed rapidly.
Mechanically the scope had a few problems. The truss tubes were attached with separate hardware top and bottom, so that setup required over 20 minutes of sorting through screws and futzing with eight separate truss tubes waving around the whole time.
The elevation bearings had been set about 1/8th inch off from each other leading to a side to side twist when the scope was moved in elevation. This was not a major problem when using the scope visually but would make the use of digital setting circles impossible as DSC’s require orthogonal axis in the scope.
The ground board was a bit undersized, making the scope prone to tipping when used at low elevation.
The rebuilt scope is essentially finished with the usual tweaking and small adjustments remaining. Things are coming out very well and a few of the changes are worth passing along to the ATM community. In the sections below I will concentrate on practical details in hope of conveying some of the finer points in telescope making.
Continue reading “Rebuilding a 12.5″ f/5 Truss Tube Dobsonian”
The lens triplet is exquisite, providing absolutely perfect airy disks at high power. The photo below shows an example of the out of focus image of Antares taken with the telescope. Pulling out my copy of Suiter’s Star Testing Astronomical Telescopes shows nearly identical images for the ideal diffraction pattern. No wonder the ‘scope won a RTMC merit award.
Photographically it has proven to be almost perfectly free of color, corrected across the spectrum. There do not seem to be any detectable UV or IR halos around bright stars. This is partly a result of good design, and aided by the long focal length of f/13. No field flattener is required, with pinpoint stars across the focal plane.