telescope – Page 20 – A Darker View

A Dew Heater Controller

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!

Dew Heater Electronics — A view of the interior of the handwired dew heater controller

This is a tropical island, this means tropical humidity and moisture. Dew is a feature of observing that I have not had much problem with in the past. In Arizona it was rarely an issue, but here it can quickly shut down a night’s observing. My last time out on Mauna Kea dew was a problem, it didn’t shut me down, but it was a constant hassle. I had to be quite careful about breathing on the eyepiece. One mis-aimed exhalation and that eyepiece needed to be put in the back of the vehicle to dry out!

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!

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A Driveway Telescope

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.

The mount sits on a custom wheeled dolly designed just for moving the telescope. To align and level the scope there are three jackscrews one at each leg to level the mount at setup. Leveling and aligning the scope is one of the longest steps in the process, about 5-7minutes to level and align properly to the Earth’s axis.

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Postcard from the Universe – Telescopes

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…

Mauna Kea Observing

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.

New Telescope Happy — Olivier beside his new telescope, a 12" Orion Dobsonian

Olivier brought his new 12″ Orion Dobsonian. And I do mean new, it was not yet fully assembled! The usual troubles of life had conspired to rob him of any time in the few days since the telescope arrived. He had assembled the main parts, the base and OTA, but had yet to install the elevation bearings, handles, encoders or the primary mirror. Thus we spent the first two hours finishing the telescope, no problem as final assembly gave the heavy cirrus clouds time to clear out.

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Mauna Kea Observing

Driveway Astrophotography and Comet Garradd

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!

Comet C/2009 P1 Garradd on 29 March 2012 showing both tails, sum of 50 x 1 min exposures CoolSNAP ES and 180mm f/2.8 lens

Thus, under a very pretty sky, I rolled the photo rig out of the garage and spent some time getting everything back together. I was not in a hurry, time to let a bright crescent Moon set a little and my primary target rise a little. The target at the top of the list? Comet C/2009 P1 Garradd.

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.

Deep Violet, an 18″ f/4.5 Dobsonian

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.

The decision process that eventually settled on the 18″ f/4.5 design was a long one. As a very active amateur I had had many opportunities to examine other scopes. To see where they excelled or where they fell short. With this experience I eventually decided on a list of requirements.

The scope had to have sufficient aperture to take advantage of the dark skies available near Tucson. I wanted to see spiral arms in galaxies.
The design was to be visual only. No drives, but provisions for an equatorial platform at a later date.
The mount would be a no compromise rigid structure, capable of allowing good optics to perform at their best.
The scope had to fit through a standard doorway.
The scope had to fit in the cargo compartment of a Ford Explorer Sport without dropping the seat for safety during transport.
The eyepiece must not be an excessive distance above the ground, allowing use while standing on the ground much of the time. (But then, I’m 6’2″ tall)

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.

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Rebuilding a 12.5″ f/5 Truss Tube Dobsonian

Some time ago my friend Bill Lofquist bought a dobsonian telescope from Roger Ceragioli. Roger had built the ‘scope to provide a home for a beautiful 12.5″ f/5 mirror he had made. The mirror is gorgeous, as is typical for Roger who is one of the best opticians I know. I have an APO triplet of Roger’s that is a prized possession.

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.

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Violet Haze, A 90mm f/13 Apochromat

I had wanted a high quality APO refractor for some time. Mostly for photographic use. Opportunity presented itself when Roger Ceragioli offered me a 90mm telescope he had finished the year before and was willing to sell. Working for the Steward Mirror Lab, Roger normally grinds very large optics, things like secondaries for six to eight meter telescopes. But as a hobby he makes somewhat smaller telescopes. This particular lens set had won him a merit award at RTMC in 2002. I had previously seen this telescope and after some negotiation we settled on a price.

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.

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A Backyard Telescope Pier

Complete Pier — The completed pier with a telescope atop

Have you ever wanted to have a place to set up your scope easily in the backyard? with instant polar alignment? no tripod legs in the way? Even for someone with little handyman experience a pier is an easy weekend project that can be completed for around $60. Add the cost of a wedge for your scope, about $125-$400 new, less used, and you have a usable pier. A few bags of concrete, a little rebar and a sonotube will do the job. I know, we ATM’s usually use sonotube for telescope tubes, but this is what it is really meant to do, cast concrete.

A pier is also the first step in a real backyard observatory, build the pier first, then a building around it. The process shown here works for any pier and can be scaled as needed for larger scopes. The pier shown in the photos is intended to hold an eight inch SCT.

The plans and photos shown here have been used for several piers here in the Tucson area and have been refined with the experience. Feel free to improve on what is here, and if your idea works well send photos!

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