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Coronado's Personal Solar Telescope TELESCOPE REVIEW Observing the Sun through Hα filters has been expensive — and often frustrating — for amateur astronomers. Now, that has changed. /// BY JEFF MEDKEFF Coronado’s Personal Solar Telescope α mount was acquired, many people had I’ve been a hydrogen-alpha (H ) junkie spent as much money for a solar telescope since my first look through such a filter 21 years ago. I still setup as they would have for a luxury remember my first view of prominences protruding past the automobile. By the late 1990s, new suppliers, limb of the Sun, filaments lying like stray hairs across its face, improved filter designs, and Hα solar tele- and bright active regions scattered around the solar atmos- scopes that were self-contained appeared phere. Although I was a neophyte, I realized immediately that on the market. Selection and performance improved. Prices dropped, but only a lit- this was a special class of observing. bandwidths, around half an angstrom (Å), tle. Hydrogen-alpha observing was still Through an Hα filter, I could see a higher the Sun’s disk is almost furry — an expensive, but more tolerable than before. layer of the Sun’s atmosphere and a whole incredible forest of contrasty details It seemed amateur solar observing might new class of features — it didn’t look any- jumps out, creating an image as memo- be entering a golden age. Still, nobody was thing like what I observed through a rable to most people as their first views of prepared for an announcement that a white-light filter. Saturn. But as the bandwidth swells, the complete Hα solar telescope soon would Through the years, I stole looks image gets washed out. The big problem appear and cost only $499 including the through dozens of Hα filters and even with Hα filters, however, is expense. As eyepiece. Like many people, I was unpre- owned a few. I quickly learned that the recently as 10 years ago, many Hα solar pared to believe such an inexpensive slimmer the filter’s bandwidth — the little filters cost more than $10,000. By the time instrument could perform acceptably, slice of the solar spectrum the filter lets a long-focal-ratio refractor (the preferred until I tried one. through — the better the view. At narrow instrument) was added, and a sturdy Coronado’s PST Coronado Technology Group’s Personal Solar Telescope (PST) is a self-contained Hα solar-observing rig. The PST is a 1.6- inch refractor that has an Hα filter sealed inside. At 15" (38 centimeters) long, it is lightweight and super- portable. It accepts 1¼" eyepieces, has a small knob to control focusing (which is done internally), and sports a ring at the base of the brass tube that allows the user to “tune” the image. There is also a solar finder, which the maker calls a “Sol Ranger,” built into the telescope’s body. According to the PST’s manual, the worst — that is, the widest — bandwidth this filter would pass was marginally less THE BLACK RING allows users of Coronado’s PST to “tune” the image. A gentle turn reveals solar than 1 Å (less, at times, depending on how prominences; turn the ring the other way, and chromosphere detail is revealed. ASTRONOMY: WILLIAM ZUBACK the observer tuned it). Tuning allows for © 2009 Kalmbach Publishing Co. This material may not be reproduced in any form without permission from the publisher. www.Astronomy.com CORONADO’S PERSONAL SOLAR TELESCOPE is ready to attach to a camera tripod right out of its case. The MALTA tabletop mount, shown here, is optional. ASTRONOMY: WILLIAM ZUBACK www.astronomy.com 79 THE PADDED CASE the PST is packed in con- tains spaces for everything you’ll need for tabletop solar observing, in addition to pro- tecting the contents. ASTRONOMY: WILLIAM ZUBACK Sun was still sufficient to watch fine movement of the solar atmosphere caused by shifting magnetic fields. I watched rap- idly moving features by tuning the PST to compensate for Doppler shift. I did not lament the fact I wasn’t using a narrower- bandwidth Hα filter, and was pleased by the view of the Sun the PST provided. I was getting the complete Hα experi- ence — and getting it at low cost. The PST supported mag- nifications up to 100x before the image became excessively fuzzy. During periods of good seeing, 70x helped reveal details not easily perceived at lower magnifications. Although I was unable to test the tele- scope on an optical bench, the views the PST provided and the mag- nification it supported gave the impres- sion of high optical quality. My PST included the optional MALTA tabletop mount ($109.95), a convenient accessory that travels in the same case as the telescope. The MALTA has smooth motions and works pretty well — this better views of cer- accessory is not a gimmick. It’s the perfect tain parts of the solar little finder is amazing. It contains height for setting the PST on the trunk of disk. Tune the PST’s filter no projecting or fragile parts, uses no a car or a picnic table, but its short legs slightly, and the chromos- power, never needs calibration, and works are not suited for deployment directly on phere is more prominent; tune accurately, reliably, and straightforwardly. the ground. Ultimately, I preferred it a bit differently, and prominences will Solar observers have wanted something mounting the PST to a photo tripod stand out. A 1 Å bandwidth is fairly wide this simple and elegant for generations. equipped with a fluid head. This arrange- for a solar Hα filter, and I expected the The PST offers crisp, clear images with ment offered somewhat less stability than view to be disappointing. I prepared no sign of ghosting (a faint copy or copies the MALTA but put the telescope at a myself for washed-out images lacking of the main image) and no significant more convenient height and offered a bit detail. When I took the PST outside for a scattered light in the field of view. The smoother motion. Attaching the PST to a look at the Sun, I had to change my tune. Sun was slightly brighter than I prefer, but tripod is easy, thanks to a ¼-20 thread not so bright that features looked washed mounting hole. Performance out. The face of the Sun was rich with With either mount, I set the PST up in One of the PST’s delights is its solar find- detail, and when I properly tuned the PST, less than a minute, and this convenience er. When you point the PST in the general I easily saw several prominences project- encouraged me to look at the Sun fre- direction of the Sun, a small image of the ing into space. quently. I found myself checking the Sun Sun appears in a circular window of semi- All the basic features one would expect three or four times a day when the weath- transparent material near the eyepiece. to see through an Hα filter were visible er was clear to see if anything was going When you center that image, the Sun is in through the PST. I especially enjoyed on. Taking advantage of temporary gaps the telescope’s field of view. Frankly, the watching prominences grow and dissipate on cloudy days was also rewarding. Once, in real time. Active regions generally I observed the Sun peeking through a Jeff Medkeff is a lifelong amateur astronomer showed the underlying sunspot if it was clear spot close to the horizon during a and hydrogen-alpha addict. large, but the contrast on the disk of the light rain while a glorious rainbow shone 80 astronomy /// january 05 /// PRODUCT SPECIFICATIONS and resulting reflections off the eyepiece glass are annoying. Various jury-rigged solutions are possible but shouldn’t be Coronado Technology Group Personal Solar Telescope specifications necessary. I suggest solar-observing equip- • 1.6-inch f/10 refractor with ment manufacturers consider this and integral hydrogen-alpha filter build in a solution. • Internal focuser 1 • Tripod-mounting hole with ⁄4-20 thread Bottom line • Built-in Sun finder When all was said and done, I had fallen • 12.5mm (32x) Kellner eyepiece in love — or at least serious lust — with the Coronado PST. The principal com- Dimensions/weight: promise the PST makes is price vs. per- 15" by 2.1" by 3"/3 pounds formance. It performs well, but not Retail Price: spectacularly. The images are good, but $499 fall somewhere short of great, especially if you have something better to compare Contact information: them with. Coronado Technology Group 1674 South Research Loop, Suite 436 On the other hand, the price is low: Tucson, AZ 85710 For better images, you would nearly [t] 520.740.1561 triple your cost. The PST is well built [w] www.coronadofilters.com and rugged — I gave it several sharp raps, tipped the tripod over a few times, and threw it around in behind me. Over the course of weeks, the its case a bit (all unintentional, of PST proved to be a delight to use, and it course), and it suffered no ill quickly became my favorite option for effects. But perhaps the PST’s viewing the Sun. strongest point is that it is undeniably convenient to Comparing Hα scopes use. It throws no obstacles Given the PST’s rated bandwidth of 1 Å, in the way of the observer I was eager to compare it with my and encourages frequent SolarMax40, an Hα filter also manufac- observing. tured by Coronado Technology Group. The PST should be a strong The SolarMax40 has a bandpass of contender for your first Hα solar approximately 0.7 Å.
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