Coronado SolarMax

The Scope
60mm, f/6.6, <0.5A H-α, BF15.
And here’s what all that technical mumbo jumbo means.

The telescope is a refractor and the diameter of the lens is 60mm. The f/6.6 means the length of the scope is 6.6 times longer than it is wide which makes it 396 mm long (but everyone says 400).

Now for the fun part. The scope has a built-in filter that mostly only lets light make it through that has a wavelength of 656.28 nanometers, which is the famous Hydrogen Alpha line, the reddish color given off by neutral hydrogen atoms when they are all excited and get their party on. Naturally there is a plus or minus to these things called measurements, a modicum of uncertainty due to various factors. With one internal H-α filter the bandwidth range gets down to +/- 0.7A, which is plus or minus 0.7 angstroms, and an angstrom is a tenth of a nanometer, and a nanometer is a billionth of a meter. So you see we are talking about some rather tiny nick picking of the photons here. My version of the scope has a second filter (the filters are called etalons which I think is French for “write a bigger check”) attached to the front end, which brings the bandwidth down to an even finer slice of +/- 0.5A. Which is nice.

By tweaking the position of the etalon slightly with a special tweaker gizmo, the distance that light has to travel to get through the filter changes enough to let through photons of slightly more or less than the magic 656.28nm wavelength of the H-α color. In other words you can change the range of the filter. That’s because you will probably want to account for the fact that the east side of the Sun is slightly blue-shifted and the west side of the Sun is slightly red-shifted. Turns out the Sun is rotating, so one side is coming towards us and one is going away. The middle of the Sun is sideways-shifting so no adjustment needed there.

The end result of all this hypertechflamboozelry, is that you can zero in on what the hydrogen is doing on specific parts of the solar surface. You’ll find that what it is doing is all kinds of circus loopty loops. The swirly bits dance about and sometimes explode right out into space. More precisely, you’ll see prominences, flares, plages, filaments, sunspots, and the granulation of convection cells across the surface. Occasionally stuff blasts straight towards Earth. Which is nice.

The BF15 tagged onto the end of the details is the blocking filter size (in mm) which reduces the total solar energy delivered to the eyepiece. You can get the scope as a BF5 or BF10 which is fine for casual viewing but for a few many precious dollars more, you get 15mm which I’m told is better for photography, more camera friendly.
The Mount
A telescope is no fun without a solid reliable mount, and I went with the Celestron CG4, which is a german equatorial mount (GEM). It is more than heavy duty enough to hold the 6 lb scope. It’s rated for 20 lbs and having more than enough is the least you want from a mount. Scopes not only magnify the images, they magnify every wiggle and wobble.

Aside from being stable, a mount needs to be easy to aim and the CG4 fits the bill. I got the optional clock drive motors that run on a small pack of flashlight batteries and since it runs like a well-balanced watch (literally), the batteries seem to last forever.

Polar Alignment
There are tricks for getting the axis of rotation of a mount lined up with the celestial pole, even though it’s daytime and you can’t find the tell-tale pattern of stars near North Star. But I rarely use these tricks for solar viewing. First of all I’ve used the scale on the side of the mount head to set the axis to my geographic latitude (48.5deg). So now I just plop the scope down in the backyard with the north leg, the one with a big “N” over it, towards my neighbor’s barn, which I know to be generally under the North Star. That alone is enough to keep tracking the Sun steady in the eyepiece for the better part of an hour. Depending on the direction of the image drift, I could give the north leg a light kick, left or right, if I wanted to. But here’s the thing. Long before the image drifts out of view, I’m messing around with eyepieces, or centering some feature I want to study, or retreating to my shop fridge to fetch a lovely beverage or something. Even if the image is out of view when I get back, it is mostly drifting along the axis of right ascension so I just push the right button on the hand-held control panel and bring it back to center. Then have another beverage.

Aiming at the Sun
How do you aim a solar scope without looking at the sun? That’s actually an important safety question, although I must confess I removed the little sticker on the lens cap warning people not to look directly at the Sun with just their eyes. The scope is beautiful, all shiny brass and black and silver, but the sticker looked stupid. It’s on my shop fridge now. Here’s what you do. Look down at the scope’s shadow. If the scope doesn’t have a distinct shadow with sharp edges, you are wasting your time trying to view the Sun anyway so put the scope away for a less cloudy day. The trick is to move the scope around in an effort to make the shadow as small as possible. When the scope is aimed at the Sun, the shadow is small and circular. Just getting close will cause a white dot to appear on the frosted screen of the little peep scope which is mounted on top of the optical scope. That’s the little tube that says Coronado. Refine the aim by getting the white dot in the middle of the screen. Voilà, solar disk in the eyepiece.
Photography
As for photography, that’s where you might want the benefit of being more critical with polar alignment. But even so, the image is bright, not like a star cluster or galaxy, which means the exposure times are short, on the order of fractions of a second, instead of minutes. Now days the typical trick with photography is to take a hundred or so images quickly, often with a video camera, one that is IR sensitive. Most digital cameras are not IR sensitive so look at the specs closely. Better yet just buy whatever camera all the other solar kids are buying. Anyway, you use software to combine a bunch of images into one, boosting contrast and bringing out the details. Use the drift method to refine the polar alignment, but it’s probably not as critical as say a 45 minute single frame film exposure of the Whirlpool Galaxy.
Eyepieces
The eyepiece that comes with the scope is the Coronado 25mm CEMAX Eyepiece, which seems nice enough and it is brass so it matches the scope. On the other hand my night-time eyepieces seem to work just fine. I ordered the full set of CEMAX eyepieces because they look cool and they are perfect for when I loan the scope out to other faculty. My Naglers are not for loan thank you. One gripe though, the full set includes the 25mm which is the piece that came with the scope so now I have two of those. That’s kind of unfair. They should let you buy the set minus the one you own, especially since everyone ordering this set owns the matching scope. The salesman told me that this issue always comes up whenever people order them. I blame the breakdown of society.

The scope also comes with a nifty hard shell travel case. Which is nice.
The Hat
If you get a Coronado, don’t forget to buy the hat. Not only so you can look the part of geek-of-the-week, but because ultraviolet light is nasty stuff. As fun as stars are, they are dangerous up close. They say the hat is UV resistant but I’m not sure what they mean by that. I assume that most any hat will stop UV. Maybe they mean that the fabric’s color will resist fading. I don’t know. At least the hat has a tail that will save your neck. Which is nice.

Prices
Here is the Coronado lineup: http://www.optcorp.com/manufacturer/coronado?cat=45
Carpe Sol