Equipment Review

Equipment Review

Coronado Personal Solar Telescope (P.S.T.)

Bill Dellinges (November 2004)

For half the price of a Taser, you can now get into H-Alpha viewing! Coronado’s $500 H-Alpha telescope has caused much excitement in astronomical circles. They can’t make them fast enough to fill orders. There was a three-month wait for mine. The 400mm F10 scope came packed in the handsome, sturdy optional travel case ($65) I highly recommend. In addition to the P.S.T, the case’s foam insert has precut spots for three eyepieces and the optional Malta table-top tripod. A 12mm (33.3x) Kellner eyepiece (ep) is supplied.

I had a difficult time getting the scope out from the foam insert - it was a tight fit. I finally removed the insert allowing me to push it through to free it. When placing the PST back, I now leave it as close to the top of this foam as possible to facilitate removing it the next time. The ep set screw played a role in this problem as it points (permanently) in a direction causing it to stick into the foam. One can cut the foam to make room for it or as I did, punch a hole in the eyepiece holder dust cap allowing the screw to be screwed fully into it. There are two ¼-20 tapped holes in the bottom of the PST to accommodate tripods. I’m currently mounting the PST on a Bogen 3221WN photo tripod and Bogen 3130 fluid video head. This gives me smooth alt-az movement using the head’s handle (and vertical drag knob). The PST has a handy built in finder. Just move the scope until the sun’s image is in the little window at the top. The instrument is all metal (excluding the plastic ep set screw) and impressively built. I did find two very minor cosmetic blemishes on my unit, a tiny score on the gold tube and a small dried substance on the e.p. holder. Had it not been for that, I’d give its fit and finish an A+. So I’ll give it an A.

Performance:

Considering its 40mm aperture, advertised bandpass of less than one angstrom at 656.3 nm, and price, I’d have to say I was impressed with this little instrument. The sun in H-Alpha, is in my opinion, THE most stunning thing to see in a telescope. But the cost for the privilege of seeing this haunting apparition was prohibitive. Now for not more than the price of a premium ep, you can join this exclusive club. Keeping the scope on my tripod by the door, I can be outside observing the sun in about one minute. I find I take a quick look at the sun every morning and never fail to be amazed at the sight. It’s especially exciting if there are prominences on the limb that I find to be more often than not. Surface detail is there, but don’t expect to see what you see through Starizona’s Day Star filter on the 6” Astro-Physics refractor. You’d be comparing the $500 PST with a $10,000 setup. Nevertheless, thanks to the PST’s handy tuner, a surprising amount of surface detail can be had. Still, if it weren’t for the prominences (90% the wow factor of this scope), I don’t think I’d pay $500 just to see the surface detail. Though I’ve heard one must tune the PST for either prominences or surface detail, I found both are seen best at the same tuner setting and focus. The focus knob and tuner have just the right feel and drag to my liking. The supplied 12mm ep‘s 33x view is just about right; you get a view of the full disk with about a quarter a sun’s spacing on each side. The Kellner12mm ep performed as well as my other ep’s (all of which reached focus) but its short eye relief will require eyeglass wearers to remove their glasses. My favorite power was 29x with a 14mm Radian that gave what I considered to be the most pleasing view. The lowest power I’d recommend is 22x (18mm ep). The highest, 40x (10mm ep).

Tips: 1) to see the prominences at their best, I prefer to move the image over so the limb I want to view is in the middle of the field. The prominence will then be at its sharpest and brightest. 2) to enhance your viewing pleasure, wear a cap with a bill to shade the ep area to avoid glare. 3) use a chair or stool for observing comfort - you won’t want to leave the ep!

There is one odd thing about the field. If you take the ep out and look into the ep holder, you’ll see the 5mm blocking filter. This is one of the integral elements of the system. Its smallness may shock you. But the sun’s image in this scope turns out to be about 3.6mm (400mm f.l./110) so it passes through it with room to spare. The “real field” is set by this blocking filter at about 0.71 degrees. The sun is 0.5 degrees. The result of all this is that all ep’s will yield, regardless of power, the SAME relative size of the field and the sun. Thus, you will not be able to make the sun “small” relative to the field as would be the case in an ordinary telescope. That is, no matter what the power, you will always have the same amount of “room” between the limb and the edge of the field. The ep magnifies both the image and the field stop. I wish that wasn’t the case. I’d like to make the sun smaller to give it more room to travel through the field. To do this, you’d need (presumably) the 10mm blocking filter (which is not available in the PST) giving a real field of 1.42 degrees. By the way, the “field stop” created by the blocking filter is not a sharp circle as in a normal scope view; it’s fuzzy. Watch the sun leave the field. You’ll see what I mean. Not a big deal, but I’d prefer to see a sharp circle cut off the sun rather than a mushy one.

Many ask if you really need Coronado’s optional Cemax ep’s. I had an opportunity to compare one to a Radian in a Maxscope 40 telescope. It was extremely difficult for me to detect any difference in the two ep’s. I thought I saw a VERY SLIGHT improvement on the prominences with the Cemax. Is the perceived nominal improvement worth the $130 Cemax ep? I think not. While the PST warranty is a generous 60 months, I was puzzled at one passage in the paperwork: “Once accepted, signed and returned [that the filter worked following shipment] any subsequent de-contacting [breaking] of the etalon filter or damage to the blocking filter is not covered by this warranty.” So once you send in the warranty, the scope is covered, but not the etalon and blocking filter?!

I like this little scope and recommend it. I think the PST provides a good value with entry level decent views of the sun in H-alpha light, especially considering the next step up in Coronado’s line, the SolarMax 40 (BF5) filter, will cost you $1265 plus a $155 adapter for your scope. To see several fine photos of the PST, go to the “Bill D” folder in the photos section of http://groups.yahoo.com/group/coronado_pst. (Note: You must be signed in and a member of the Coronado_PST group, Just click on the Join This Group button near the top of the page).