Some Sun From Appenzellerland - 17th February
Commitments on a weekend have meant that february hasn't offered me much in the way of chances for solar observations. However as was flying to Switzerland to visit CERN I was not going to miss the opportunity to stop by and say hello to my good friend from the Solar Chat Forum - Swisswalter!
Walter lives some 700m asl in the Swiss Alps in a lovely village called Wolfhalden. Despite the morning dawning cloudy it soon became apparent there were going to be some nice breaks for solar observation.
While we waiting for the breaks to materialize Walter kindly showed me his extensive collection of telescopes - at least 14 I counted, and also his extensive collection of astro accessories. It wasn't very long before we had dismantled (and reassembled!) most of Walters scope collection to see what was inside, how they were put together and how they worked. We naturally then turned our attentions to scope modding, and Walter kindly allowed me to retro-fit his PST etalon assembly with an 'acrylic ring' to help centre the important glassware. Many drawings were produced as we discussed 'creating' several new scopes, with the traditional PST etalon and also using a Lunt 50mm etalon; collimating lenses and refocussing lenses were hot gossip!
We had some very interesting discussions on the Lunt CaK filter, and after thoroughly disassembling Walters B1200 and seeing what it was made up of and how it worked turned our attentions to Walters extensive collections of bits and bobs, all stored in a particularly elegant glass fronted cupboard seen below, discovered that he had a 393nm 10a shortpass filter. Visually this appears to be identical to the very front filter from the CaK PST that I use with my Baader K-Line to get narrow band CaK images with my home brew setup. A bit of very crude spectroscopy with a angled CD showed that the 393SP and the CaK Pst front filter are very similar if not identical things. Walter is going to test this theory the next time the sun returns properly to Appenzellerland...
Meanwhile, as we pontificated on the finer details of solar modding the clouds were getting ever thinner and the sun was starting to cast visible shadows, which for a poor weather suffering Englishman like me is cue to go out an take a look at our star!
Walter had his 100mm Lunt scope set up on the Losmandy G11 mount, and with a 16mm Televue Nagler eyepeice the views were certainly impressive. It was my first view through one of these pressure tuned Lunts and I have to say I was very impressed with the view. Bear in mind all my large aperture solar scopes are variants on the PST mod, and as such are troubled with the dreaded sweetspot, where bandwidth and centre band pass vary towards the periphery of the field of view. There were absolutely no issues of this with the Lunt 100, and compared to my PST mod the bandpass was also much tighter with the filaments being much darker and easier to see.
Given this was the first sun in Appenzellerland for over 2 weeks and we were all still merry from the night before proceedings as you can tell we were all very happy solar observers, and despite the near freezing temperatures and foot of snow in Walters garden this did nothing to dampen the mood. Despite the expense of these 'off the shelf' scopes, viewing through the Lunt 100 has certainly proved to me that if you can afford these things that they are definitely worth it - lovely even field of view from one side of the solar disk to the other! In the mean time we had donned our Charlie Bates Solar Astronomy Project solar glasses and hats in respect to the fine club that we are members!
Now as if things could not get any better, Walter decided it was time to bring out his Coronado SM90 etalon to double stack the Lunt 100 to create the infamous 'Luntanado' as originally created by Jim Lafferty. I'm used to a double stack in the form of my DS40 scope, but at over twice the aperture of mine the views that this setup afforded were phenomenal. I can only imagine that if the skies were totally free of cloud we would have delayed our departure time to head to Geneva and spent a little while longer taking in the detailed views that this scope offered. The only (very) slight downside of this setup was that the images were slightly dimmer than we might have liked due to the intermittent and variable cloud, and also the extra ERF in the chain from the SM90. The SM90 in this case is the newer Solarmax II design, with it's rich view tuning, now as you might expect myself and Walter discussed at some length the removal of the ERF from this etalon housing, however, it would appear that it is integral in the 'rich view tuning' this etalon offers. It should in theory be possible but would have to be replaced with some optical plate glass for this to work. This was also interestingly my first views of this richview tuning arrangement and it is fairly obvious how it all works: Essentially the tilt wheel on the mounting plate allows you to throw the reflection this second etalon makes in the double stack setup, but then the richview element allows you to bring the etalon very finely to the ideal position to get the etalon online and onband to extract maximum contrast and hence detail. Interestingly the richview pivots the etalon around its centre spot and then by definition halves the angle across the face of the etalon by which it is been tilted perpendicular to the optical axis. This will have the net effect of reducing any banding associated with this design of external etalon compared with tilting it at the circumference of the etalon. This is actually quite a clever yet subtle development in terms of tilting an external etalon, and is something that I will look to implement on my DS40. I'm going to look at the Richview system a bit more in a coming article on here.
Till the, I would like to thank Walter and Barbara for their hospitality and giving such an excellent time in our stay in Appenzellerland! I hope to see you both again soon!
