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OKIE-TEX STAR PARTY HAS EMBEDDED ITSELF IN MY SOUL.
I realize that now as I write this a few months after the event, as the grey skies of winter hang over my shop and clouds attempt to keep my eyes from ever glimpsing a ray of sunlight again.
Why is it embedded? Well, it's the closest thing that I have found to the darkness of my childhood home in Michigan, and that is necessary part of my year. While we have to contend with some dust and natural skyglow, the skies are basically free of man-made light pollution. Next, the people I see there are familiar, from the ranchers sitting on the bench in front of the main building, to the staff who keep it running, to the attendees whom I see there annually. Also, the usually clear fall weather reminds me of the fall season in the great lakes area, where dry, clear fall weather was often the norm, and clear dark nights were the result. This means often the skies seem like they're TOO clear, and we suffer from a lack of sleep after only half of the star party has gone by. (Personally, though, I have no problem going to sleep when it's clear if I am tired. I feel no guilt in this situation!)
Of course we always check the weather forecast carefully as a star party approaches because it's not fun to arrive at an event without the proper clothing and gear. As you can see below, the forecast was for very warm weather, and generally clear conditions after the early weekend. The streak of clear weather Saturday through Friday is quite typical for Okie-Tex during most years. Because the area is dry, the temperatures don't feel quite as hot as the numbers indicate, but it looked like it would certainly be a good week to stay in the shade during the day.
The wind forecast indicated that it would be a bit breezy at times, and this is also part of the normal Okie-Tex experience. It can be quite windy or calm, it just depends on the night and sometimes the time of night. Usually the winds calm down during the night, but this is not always true. Be ready for anything! For me, I'm used to the wind, living on the prairie in Illinois, but others who come from different parts of the country may not be. Be prepared for it, and make sure your tent and other equipment can handle it.
With rain possible on Friday, John Pratte (of JPAstrocraft) and I decided to leave from Illinois on Saturday. We made the drive out in the usual two days, well really a day and a half, and we arrived in the mid-afternoon of Sunday after having lunch at Subway in Boise City, OK. We brought with us a used 25" telescope that John was delivering to its new owner at the event, and a 32" f/3.6 built by John.
A lot of other people made the trip, too. The observing fields were filling up. Attendance was over 500, a record for Okie-Tex. There was talk of enlarging the east observing field for 2016. I was very pleased to hear this.
The photo above shows the typical scene, telescopes under covers awaiting darkness, looking southeast at the ridge. Often a few clouds were around during the early evening, the remnants of some thunderstorms that were firing up during the day over neighboring northeast New Mexico. These clouds would drift in, and occasionally a little precipitation would make it to Camp Billy Joe later in the week, but it did not cause any major issues.
Occasionally the clouds would make for an interesting sunset, though the ridge to the west blocks most of this. It is good, though, because as soon as the sun goes behind the ridge telescopes can be uncovered and allowed to cool before it gets dark. This gives the optics a decent head start on cooling, which is needed there when the days are warm.
In our local area on the field, set up within about forty feet of each other, we had John Pratte's 32" f/3.6, Joe Wambo's 32" f/3.6, Christina's 30" f/3.3 Super-FX Starmaster, and just down the row a bit was a 14.5" f/4.0 FX Starmaster. Other instruments came and went during the week in the surrounding area.
The 14.5" f/4.0 is seen in the image to the right, with its owner graciously posing for a photo to show how perfect the eyepiece height is for the height of his eye. It is an ideal telescope for him, and I enjoyed some very nice views courtesy of him and the 1.25"-thick, fast cooling mirror that I made for it.
Joe's latest telescope improvement/modification had been to replace the furniture-slide mirror support points in his mirror cell with delrin pads. This reduced the friction significantly and eliminated some astigmatism that would show up from time to time as the mirror stuck to the old supports, distorting the optical figure. Throughout the whole star party, stars were unquestionably round, so the change was a complete success and has really enhanced the performance of the telescope.
We had noticed this issue popping up quite a bit at the 2015 Winter Star Party, and there we discussed how to fix the problem. Until that time I had not realized what the old contact points were made of, and as soon as I saw them the cause of the problem became evident. Joe followed through with the fix, as he always has with many modifications he has made to help his telescope perform better both optically and mechanically. Simply put, he cares deeply about getting the best out of his instrument. With a lot of work from Joe and some money invested, it has evolved into a superb instrument that I enjoy using whenever I can.
The difference between the Winter Star Party and Okie-Tex, in terms of star testing, is quite amazing. At WSP the difference in temperature between night in day is not large, so mirrors equilibrate during the night more quickly. Also, the normal sea breeze there helps optics equilibrate, too. However, at Okie-Tex, optics will often have a hard time keeping up with falling temperatures, especially during weeks like this when it is hot during the day.
I have done quite a bit of star testing of large cooling mirrors, but at Okie-Tex even I was fooled by a star test in a large telescope. I thought that something could be wrong, but I realized that I was quite wrong. When I compared the star test of the mirror in question with the star tests of other mirrors that I knew a bit better, such as John's 32" f/3.6 in particular, I knew that my star testing was in error. In the Florida Keys, after it equilibrates, both John's 32" and Joe's 32" show nearly identical intra- and extra-focal diffraction patterns, but at Okie-Tex they certainly did not! The reason is simply that a cooling mirror temporarily changes shape until the temperature within the glass equalizes, if it does at all. (For more on this phenomena, see my article "Four Lessons in Mirror Testing".)
The article and my experience at Okie-Tex show that star testing is very difficult and easy to mess up, and star tests cannot always be trusted to give good information about a mirror's figure. Bench tests are better for that. This was also one of the conclusions in one of the talks that I presented on Thursday afternoon, so I should have listened to my own advice! I'll blame a little lack of sleep for my temporary stupidity.
Below Joe's 32" points high in the sky as a few clouds pass by to the south, and a couple of airplanes make their presence known in the image.
Really, I find that star testing is only useful when you can do it in different locations and over many long nights to see how the cooling of the mirror affects the shape of the optic. Then you can approach some reasonable accuracy, but you may not be able to separate out the shape change caused by cooling.
Also, if not using a SIPS, one must be careful to set the tunable top of the Paracorr properly or else spherical aberration will be introduced, and this will throw off the star test quite a bit. (Some of the eyepiece/adapter combinations that result in the proper corrector to eyepiece spacing are not commonly known - for certain 1.25" eyepieces, you must use a certain type/height of 1.25" adapter to yield the right spacing and proper performance.)
It might have been on Sunday or Monday night that the seeing was quite good, and powers of 600x to 800x were being used. The Veil Nebula was beyond belief in terms of the detail that could be glimpsed under such conditions. Other objects high in the sky provided some best-ever-type views. Stephen's quintet was a detailed Stephen's Sextet through the 32"s.
I still believe that observing how tightly a telescope focuses is often more accurate than the classical star test, especially for large mirrors, and this was true on this night. While the star tests looked poor, the telescopes were focusing sharply at these high powers. This is always a good time to compare and see what telescopes are focusing the best, and then to try to figure out why.
However, the party was soon over. At almost exactly at the stroke of midnight, with no warning, a rustling was heard on the ridge, the sound of a gust of wind percolating through the scrub brush and small trees up there. A cool breeze blew in from the southwest and the seeing instantly went from quite good to very poor. At this point many of us called it a night when it became apparent that the good seeing would not be returning any time soon. Sleep is good.
This star party is a good one to just sit around and relax, especially after the sun goes behind the ridge. Below, at left, John Pratte sits. At right, Kirk sits - he flew in for a weekend to enjoy some dark skies with his kids and play a bit of golf.
Above, at left, Mike Dennis, currently the head-honcho in chief (HHIC) of the Okie-Tex Star Party, sits. During the day he is usually running around getting necessary things done. Above at right, the other support staff sit and try to catch a nap because they are either working hard keeping the star party going or imaging all night, or both. There is a lot of work involved in running and organizing a star party, so when you attend one, make sure you thank the staff.
The image below shows the view from where they were sitting, which is quite nice, I think.
Below, Dave and a friend of his sit as the sun sinks behind the ridge. Dave now has a 12.5" f/6.5 Teeter telescope with a 1.1"-thick mirror made by me and a mirror cell made by JPAstrocraft. It was not quite ready as of this event, but as of the writing of this, I can say that he now has a fine telescope that saw first light at the Chiefland Fall Star Party (my report).
For the time I was there, we only had clouds for half of one night, if I recall correctly. It clouded up at midnight, and cleared in the early morning, and this was perfect for getting some sleep. Personally, the latest I stayed up was ~4am on one night. Once I see the winter sky rising I usually am content to leave that observing for the Winter Star Party where it is up higher and up high as it gets dark, and the seeing is better. Transparency is usually better at Okie-Tex, of course.
Above are a couple of random images, above left Joe, and Jon Joseph, and Howie Glatter discuss Jon's motorcycle. Above right the Milky Way stands up early in the evening over Joe's observing ladder.
Above Joe observes while my camera tracks the sky. Sagittarius appears just above his head and the telescope.
In the image above Doug observes through Christina's 30" f/3.3 Starmaster, and the sky reflects in the primary mirror. On the horizon at right a cloud reflects the only light pollution that you'll see at Okie-Tex, from a distant unidentified town, and only visible with a cloud to reflect it. This view is looking northeast.
The image above shows John Pratte's 32" telescope at left, and Joe's 32" at right. It is wonderful to be able to go back and forth and look at different objects in large telescope, and we also had Christina's 30" set up behind me and to my left as I took this image. We were in the triangle of aperture.
Here John Pratte sits some more as his telescope awaits darkness. You can see the cooling fan, suspended by thin stainless wires in front of the primary mirror, blowing on the front surface and helping to cool the mirror symmetrically front and back. This is the best cooling strategy that we have yet found. Joe was one of the first that I saw using it, and his 32" has had one of these fans for years now.
Above another group sits in the afternoon, shaded by some afternoon clouds. While there are many sights to see in the surrounding areas if you are motivated to get out and take a road trip, I am usually content to relax on most days and just slow down life.
Of course a snack is always good, and pretzels are great food for camping (image at right). While enjoying some snacks with this group, a cloud passed overhead and dropped some small hail pellets. They were harmless, but unexpected and caused a few people to scramble and cover things.
Joe and I played golf on a windy day in Clayton, NM, met back up with Lisa afterward, and then visited Clayton Lake. We walked around the lake and saw the large area of dinosaur footprints. The lake is totally unexpected out in the grasslands as you drive there, and eventually you come upon it and are surprised at the sunken oasis in the semi-desert grasslands.
After working up an appetite, we visited the Hotel Ecklund restaurant in Clayton, which featured good food, some interesting microbrews and interesting ambience.
On Thursday I gave back-to-back talks, "Four lessons in optical testing", and an informal talk about mirror cells and secondary holders based on my online web article. I will be making slides and presenting that talk at WSP 2016. Links to the article version of these talks are found on my Articles Page.
To burn a few calories, I ran (literally) over to Kenton a few times, and up through the cemetary on one occasion. I tried to do this in the morning before lunch to avoid the mid-day heat.
In other star party news, at one point one of the flamingos on the ridge went missing, likely due to a strong breeze, but we blamed coyotes or terrorists to make it more interesting.
This year featured an increased ice supply due to larger attendance, with the proceeds going to the Oklahoma City Astronomy club. The food was typical Okie-Tex, but I received a very large helping of salad one night thanks to a special arrangement from the staff. I ate it all! (Yes, guys, there are more food groups than beef and dessert.)
Speaking of eating, here is some of the staff having dinner. Thank these guys if you see them, and offer them a salad.
Skies were fairly transparent this year, but there was a little more natural skyglow than other years. SQM meter readings were around 21.5 to 21.6. I took many images over one night, tracking the sky, to show a time-lapse of people observing as the stars stay fixed and round. I am still working on getting that put together. I used a 14mm f/2.8 lens for time lapse shots, and my Canon 5D Mark III, all on an iOptron Sky Tracker mount. I shot some dark frames afterward.
A large number of people come to Okie-Tex just for imaging, and they usually get 80-90% clear nights, I would estimate. That's great for gathering data, especially under very dark skies.
Below I'll leave you with one final image of Joe and Lisa observing as the Milky Way blazes above them. For me, it is my favorite photo of the event, the one that sums it up best for me.
I wish you clear, dark skies, calm winds, big telescopes with good optics, and good friends to share all of that with.
-Mike Lockwood, Lockwood Custom Optics