Sunday, November 29, 2015

A Telescope's Second Life!

It is said that a home-built telescope is never finished. Likely true as a commercial version upon which thousands have been spent are likely never to be touched by their owners outside a dusting of the mirror or lens. But one built with your own hands in your workshop are easily tweaked or modified to meet one's changing needs. Case in point has been my 11.25" scope built late in the last century... On the long drive back from the Riverside Telescope Makers Conference a couple decades ago, my mind full of new ideas, I was thinking of a "fast" telescope system (needing only short exposures). Besides a short focal length, it would feature a built-in guide scope that would minimize deflection between the scopes that would lead to trailed images. The result is shown at left, set-up at a Kitt Peak Star-B-Que in 2010, likely the last time it was used in that form. Check the link for commentary on the star party and a nice collection of images taken that night. For a home-built, it worked pretty well - the guide scope actually focused through the main scope to the silver focuser, where manual or autoguiding could take place. Off-axis stars were easily found by adjusting the small 5.5" guide mirror's collimation. My favorite from that evening is shown at right - 17 minutes on a supernova remnant called the Veil Nebula - an outstanding result from a short set of exposures.

While the scope was a little unwieldy with the weight and mass distribution of the guider telescope, the focal length was perfect (about a meter), and the speed, about F/3.5 allowed exposures of only a few minutes. What spelled its doom as far as being my "go-to" scope was getting the Hyperstar attachment for the C-14 scope. With the larger 14" aperture and faster-still (F/1.9!) optics, it had a wider sharp field of view with nearly equivalent exposures less than a minute! Also, if you wanted to switch to visual observing, slip out the Hyerstar, put in the secondary and you had a C14 with its excellent optics. But I missed my lil' home-built! We had spent a lot of hours together in figuring the mirror (twice, to get the curve just right!) and building the thing. And we had won prizes together - both a Merit Award when it appeared at RTMC. and again a few years later when we saw all 110 Messier Objects on a single night at the All-Arizona Messier Marathon, when for a week or two in the Spring, you have the chance to track down all of Charles Messier's little fuzzies he cataloged as he hunted comets in the 18th century. Plus, the longer focal length allows a little larger scale of celestial objects.  So I was thinking of resurrecting the scope...

In reality, telescopes are simple devices. The tube of the scope rigidly mounts the optics and focuser, along with any other ancillary optics and accessories. The glass is fragile, and the mechanics of a focuser are beyond most, otherwise there is little complicated in one. Shown at left is how the scope has been in stasis since that Star-B-Que 5 years ago. At right is a view down the working end, and you can see how I made a simple spider to hold the secondary mount, and you might see how the guide scope at left is focused through the main scope to the silver focuser at right - handily next to the camera mounted on the main scope.   Besides removing the guide scope to make it lighter, the only changes I had in mind was a new set of commercial rings from Telescope Support Systems, a small garage shop run by some friends in Michigan, and a focuser to replace the plastic-and-PVC version I'd started with so long ago. I decided on a sturdy 2" focuser from Antares for $180 - seemingly a good step up.

After removing the primary mirror and cell, I reached up the tube and removed the nearly 20 bolts with which I had attached the guide scope to the main tube. The guide scope then came off without any issues. The new tube rings went on perfectly! They had wanted my tube dimensions to a couple thousandths of an inch, and I had 3 ways to measure and report it to the company for accurate machining, and it shows in the product. The two saddle plates I got do double duty - one side attaches to the mount, the other holds the new, much smaller guide scope that I use now for accurate tracking. The new installed rings are shown installed at left, the new focuser still in plastic on the right. After some careful measurements and layout, I drilled 4 new holes for the focuser and attached that too, so literally, in a couple hours of work, the scope was reconfigured and brought back to life. It is now much lighter and easier to manage by myself, and occupies a seat of honor in the van with its own special seatbelt made of a couple clamps and 2" webbing from REI! You might have spotted its initial use here in Tucson at friend Dick's house when he held a little star party early in the month. I mounted it on an alt-az mount designed and built for my TEC 140, but worked fine for some wide-field views through the 11".

I was able to get out for a couple partial
nights to a friend's house near Benson. Not perfectly black skies, but plenty good enough for some trial runs. Shown at left it is mounted on the AP1200 mount. When I acquired the mount a couple years ago, I got a stumpy pier for use with Newtonian scopes, but never used it till now. But the combo seemed to work well, though I've got to crawl on the ground to use the Polaris scope to align the mount to the Earth's rotation axis. And once done, I forgot to lock some of the adjustable bolts the first night out allowing some trailing... The entire huge guide scope I took off has been replaced by the little white scope between the tube rings at left and a digital autoguider camera. You no longer need anything close to the focal length of the main scope (the old standard 20 years ago) these days... Because of the mentioned trailing issues due to some loose bolts, the images aren't too impressive, but I was able to collect 7 frames of 3 minutes each on NGC 891 shown at right. Blobby stars, but shows some promise. Still getting some weird diffraction patterns around brighter stars - saw that also on the earliest images from Dick's house.  I originally blamed it on the coma corrector extending into the beam, but I'm thinking there may be a turned down edge too...

The next time I was out to Benson and Pat's (the night of the Trident Missile launch on 7 November), I made sure to tighten all the bolts, and also made a mask slightly smaller than the mirror to block unwanted diffraction. This time the seeing was poor, but was still reasonably dark. At left is shown a fisheye picture (8mm lens for 90 seconds) showing our sky with Roger Ceragioli's newish 11" refractor and my 11" Newt working side-by-side as the Winter Milky Way started rising. Finally, just as we packed it in, I took a few frames of the Pleiades rising in the east, of which only 2 frames were suitable for stacking. So this is 4 minutes total exposure, with some cropping. Stars are excellent, as are the diffraction patterns. The Pleiades sits in the middle of a dust cloud, which is illuminated by some of the stars here. Note on the right side, about an inch from the edge when looking at the full-size image, there is a little edge-on galaxy halfway from bottom to top. I'm looking for the name of that guy and will report it here if I find out. Anyway, I'm thinking the scope is showing promise again as I get back into some dark sky imaging. Stay tuned!

It has a name!  The lil' galaxy near the Pleiades was tough for me to track down, but thanks to professional astronomer Brian Skiff of Lowell Observatory, who did all the heavy lifting in IDing it, it has a name.  It is UGC 2838, nearly 350 million light years distant (!).  The Uppsala General Catalogue is a catalog of all galaxies brighter than magnitude 14.5 north of the Celestial Equator, using the first generation of the Palomar Sky Survey as its source material.  The image at right shows a little closer view with the galaxy indicated - again, only 4 minutes of total exposure, so you shouldn't expect much!  In some of the writings about it, its brightness is quoted as nearly 18th magnitude, but in others it is listed at about 15th magnitude - still faint by visual standards, but obviously easy to catch photographically with the 11"!

1 comment:

Anonymous said...

cool image of galaxy ugc2838