A Visit to Coronado Instruments

Martin Willes

During this past February I had a chance to visit Coronado Instruments in Tucson, Arizona, while visiting my father. The day that we had planned to visit Coronado was the first day that I encountered clouds my entire vacation. I was a little apprehensive about making the 11/2 hour trip from my father's home in Queen Creek, Arizona, only to arrive in Tucson and have the clouds ruin our day looking through H-Alpha filters. Astronomy has been my hobby for a number of years, and since I live in the Midwest, weather related disappointments really don't affect me anymore. We decided the day was planned for this trip so let's get on our way.

The drive down highway 79 was beautiful with Saguaro cactus, indigenous only to this area, popping up all along the highway. We soon passed the Biosphere 2 project near Oracle Arizona and the clouds began to break. By the time we arrived in Tucson the sky was mostly clear and temperatures were in the upper 70's. At Coronado there was an employee setting up a Solar Max 90 on a Tele Vue 102 refractor in the parking lot for testing. We walked in the office building to have a look around and were surprised by the number of employees that worked at Coronado. I was told that day there were 23 employees between the manufacturing building and the office building. I had always thought this was a mom and pop operation. Within a few minutes two other telescopes had been set up for our viewing pleasure. One scope was a Takahashi Sky 90 refractor set up to look at the Sun in white light with Coronado's "better white light filter". We used Coronado's own Cemax eyepieces on the Takahasi to look at the Sun. I thought the view was about as good as Baader Film but did not have quite the resolution of a Herschel Wedge. I didn't expect the resolution to be as good as a Herschel Wedge, but I did like the fact that we were looking at the Sun through a piece of pin hole free optical glass and not a thin fragile sheet of polymer film. We were here to look at the Sun in H-Alpha, but it was a bonus to view the sun through a high quality white light filter.

By now the Tele Vue 102 was set up with a Denkmeier Binoviwer and it had 25 mm Coronado Cemax eyepieces in it. I was in for a real treat because I had never looked through a 90mm Coronado H-Alpha filter in good observing conditions. Coronado has been good enough to make it out to a couple of Astrofest star parties in the past but the weather has never fully cooperated. I thought that I was going to strike out again because we were looking out over a parking lot and it was close to noon, so the views should be bubbly to say the least. What I saw through the eyepiece was nothing short of amazing! I've been observing the Sun in H-Alpha for 11/2 years and I've never seen prominence detail and contrast like this. I could easily have looked at the Sun all afternoon. Plages and filaments sharply stood out against the deep red solar "surface". The Sun had a three dimension feel to it and I couldn't keep myself from scanning the entire disc at high power. The resolution and detail were incredible. Magnetic lines were a snap to trace back to the Sun. The prominences had a twisted, smokey, almost three-dimensional look to them. I took my time at the eyepiece trying not to stay at the telescope too long, but every time that telescope freed up I was back feeding my addiction. There was a third telescope set up to look at the Sun in a more narrow band pass. The Maxscope 40 refractor is a telescope that Coronado sells as a dedicated H-Alpha telescope. This telescope has two H-Alpha filters stacked on top of each other to yield a band pass of .5 angstroms. The advantage of this configuration is to see more disc detail on the Sun. The detail in the disc did have more contrast but I thought the resolution was poor due to the small 40 mm aperture and the fact that the light had to fight through more glass before it reached my eyes. I've had better resolution with my own 40 mm Solarmax on an average refractor.

We looked at the Sun for about an hour and I was starting to think that the two Coronado employees had better things to do than entertain my father and I. I asked the sales manager if it was possible my father and I could have a look at the manufacturing facilities. I had fully expected for him to say no, but instead he went into the office building and asked permission. We were granted permission so long as no photographs were taken. We were given a very fast birds eye view of the manufacturing process. In one room there was an employee placing the spacers between the glass etalons. This is a critical step and he was taking great care in the placement of the spacers and constantly cleaning the glass surface. These tasks had to be performed by this technician while separated from his work by a sheet of glass. I assume the glass was to keep impurities off the glass surface. In the same room another man was fitting the etalons into their metal housing. The etalons are kept snug but not too tight in the housing by what appears to be a foam strip. I'm told the critical spacing of the etalons should last forever so long as they are not dropped. Outside of this room just a few feet from the door a vacuum chamber was coating some optics with Coronado's own hard coatings. In another part of the building I could see a shelf with glass blanks on it and a machine grinding the glass blanks into etalons. There were employees returning from lunch to work so we concluded our tour. There was a metal fabrication facility on the other end of the building where Coronado makes their metal cells and adapter plates for various telescopes. I was very impressed with the operation and I had no idea that Coronado was so large.

If you ever get a chance to look at the Sun in H-Alpha light, don't pass that opportunity up. You will be looking at an active layer of the Sun's atmosphere called the chromosphere. The chromosphere is located 10,000 km. above the photosphere. The photosphere is where white light features such as Sunspots can be seen. Hydrogen alpha can be found around 653.3 nm. The Coronado H-Alpha filters reject all light except this very narrow region of the Sun's spectrum. This narrow band pass allows you to see solar flares, prominences, filaments, spiculae, and ficulea that occur in the chromosphere. When there are few sunspots to observe in white light, you can almost always find something interesting happening in H-Alpha.

If you want to learn more about how Coronado H-Alpha filters work, go to their web site and click on "technical information". I could fill up a half dozen more pages with the information from this web site:


Here you will gain a basic understanding of how a filter that doesn't require electricity can separate the Hydrogen Alpha portion of the spectrum and reject the rest. Coronado developed their filter technology by doing work for NASA. The filters are thermally stable between the temperatures of -138 degrees to +138 degrees. Currently Coronado does outsource some of their work, but by the summer of 2003 everything will be made at the Tucson plant. The people at Coronado certainly made my father and I feel welcome.

Published in the April 2003 issue of the NightTimes