Part 3: Novice Imaging Webcam Tests - The Sun

New telescope!

In late spring 2006 (immediately after the end of the worst rainy season in No. California since about 1983) we purchased a new instrument, desiring a convenient semi-permanent setup to use for casual planetary/lunar viewing in our front driveway. We chose an Orion SkyView Pro 120mm aperture achromat refractor, enticed to buy it when we purchased the mount for our Orion ShortTube 80 refractor (not a particularly effective planetary scope due to its short focal length.) It cost merely $200 more to add a very good longer focal length, larger aperture refractor to the purchase of the mount; and we got a discounted package price for both. The 120mm refractor has a focal ratio of f/8.4, a good compromise between the 'standard' f/15 achromat design for best color correction but narrow field and high power, and the wider field width and lower power of a shorter focal length, at the expense of some image sharpness at high power and best possible correction of chromatic aberration. Indeed, the f/8 design allows a certain amount of use for photographic purposes, as well as low power for wide field views of large-angular-diameter galaxies and nebulae.We did find it necessary to add an extension tube to the German equatorial mount, to prevent the necessity of sitting right on the ground in order to be able to see objects at the zenith. Since the extender increased the mass and changed the resonant frequency of the system, more shaking was evident. So, we added three adjustable trusses, comprised of various bits and pieces of hardware: electrical conduit splices (at the feet of the mount, to anchor the truss members), three turnbuckles, and six pieces of bent aluminum stock, hooked to angle brackets that were screwed under the fasteners at the top of the extension. This mechanism works very well to restore the stability that the mount had without the extension tube.

At present, we've opted to use the mount without a right ascension drive motor since manual adjustments of the RA control during high power planetary viewing are not at all troublesome. And sometimes one can see finer detail if the image moves -- or if the eye scans across it. We have enjoyed struggling for good views of a low-altitude Jupiter, trying to get glimpses of the 'new' second red spot, just barely visible in May 2006, and of the higher (and much steadier) Saturn. Lunar detail is spectacular: bright, crisp, and clear, with virtually no trace of false color. Deep-sky observing with the scope during two nights around the late April new Moon, when ground fog cut off all the Santa Clara valley light pollution on the top ridge of the Santa Cruz mountains, were mightily surprising: we found many galaxies in the magnitude range of 11 to about 11.7; viewed Barnard dark nebulae in the southern Milky Way region between Sagittarius and Scorpius; and enjoyed the Veil Nebula, visible even without a filter. Double star resolution is wonderful, with "textbook perfect" Airy disks. As the saying goes, "you could drive a truck between the members of the 'Double Double' in Lyra..." In short, the new telescope is a delight to use and sooner or later we will put up a complete review of it here on this website.

The picture above shows how the Orion ShortTube 80 mm refractor is mounted atop the SkyView 120. This richest-field 80mm aperture refractor serves the purpose of being a second finder scope, as well as an ultimate low power scope for brightest possible views at the widest field. A 90-degree correct image diagonal is attached to the ST80 so that eye views resemble the layout of a printed star chart, making star-hopping to faint objects as easy as possible. After this picture was taken, we changed the mounting rings to ones designed for large guidescopes, permitting careful directional adjustment to agree exactly with the eyepiece view in the Orion 120.

At last, we had an excuse to get a good quality neutral-density solar filter for observing sunspots. I took this webcam shot, showing an Orion full- aperture filter in the safe and secure mounting box I contrived for it. This will suffice until we go one step further and obtain a narrowband solar prominence filtering system to upgrade the old Lumicon 1.5 Angstrom unit that we used to struggle to use, despite its low contrast and fussy tuning. The newest generation of solar filters offers better value and performance at lower cost, so a 1-A model is definitely on our "want list" for the future.

As soon as we had perfected the balancing and stabilizing of the rather complex system of this dual-refractor (120 and 80mm scopes, 9x50 straight-through optical finder, and "red dot" sky sight) we wanted to find out if it would be practical to try some digital imaging of the Moon and planets. Since we have not yet added a right ascension motor, the scope would have to be used to produce a continuous video of a drifting field, obtaining short-exposure frames that could be aligned and stacked. This would be a very tedious job, indeed! But it was just barely possible, with a great amount of patience, using a small sunspot group near the solar limb as the study subject.

We employed our modified Logitech webcam, which lacks the excellent color accuracy and sharpness of the superior models, such as the legendary Philips ToUCam, or the Meade LPI (as we showed in Part Two of our "Digital Astro Novices" articles.) But, we got a usable short video file in AVI format of about 25 seconds on our third or fourth try, running back and forth from computer to scope to tweak the positioning and then start the video recording process just as the sunspot drifted into view. But, the seeing was rather abominable (as it often is during afternoons; frequently the best time to view the sun is the early morning, after it has risen above the fuzziest air near the horizon.)

As unimpressive as the AVI file looked "raw", we wondered if it would be worth the trouble to process it into a still image. (Click here to see a data-compressed lower res version of the original video, converted to a 248 kilobyte Windows Media Video format file.) But, we have made some definite progress in using the many functions of "RegiStax", the wizardly frame stacking/image processing program used by many astro-digitizers, as the end result shows below!

Of course, we also did a lot of tweaking with a standard graphical editing program to do unsharp masking, contrast stretching, and color correction. Though the digital quantizing of the original 8-bit image caused irritating discrete brightness steps after the processing by RegiStax, we were able to massage those out somewhat and to restore some of the quality of the image as seen in the eyepiece. There is probably about as much art as science in the final result, so we can't claim that this image is perfectly accurate. But, it's a promising beginning...