Wednesday, January 30, 2013

2013: Star Party Bonanza!

My summer schedule is usually all over the place, and if I can make it to one star party I'm doing well. It seems sometimes like all the new moons fall on busy weekends; if it's not that, there may be several star parties at the same time. Then there's the Minnesota State Fair baked goods entry day, the August Sunday fifteen days before Labor Day.

"Fairchild," mascot of the State Fair.
What, you've never seen a gopher wearing a bow tie?
For a few days leading up to that I'm usually baking furiously in preparation. What can I say, I like baking bread, and I like winning ribbons.

The Ribbon is what it's all about.
Disagree? Get your priorities straight.

And on top of all that, there's earning a living. Oh, to be retired and financially secure! Years to go before that happens, if ever. I teach Friday night and Saturday afternoon science courses that typically run through the end of June. That puts a crimp in attending the usual Thursday through Sunday parties.

Amazingly, this year four parties fall on open dates for me:

  1. Wisconsin Observers Weekend, near Waupaca, WI. This was my only summer party last year, and I really enjoyed it. In 2013 it's in June, on an off weekend for me!
  2. Jeffers Petroglyphs informal party (nee Prairie Grass Stargaze), near Windom, MN. My favorite star party. Hard to do better than the people who stage this and attend, and the setting is made all the more sublime knowing that an ancient Native American observatory has been found nearby.
  3. Northwoods StarFest, near Fall Creek, WI, and hosted by the Chippewa Valley Astronomical Society. Never been to this, but it's close and most people speak highly of it.
  4. Iowa Star Party. I've missed this for the last few years. This is where I was introduced to real astrophotography by some very nice imagers. Someday I hope to exact my revenge.
I don't know if I can handle all this dark site time, but I'll try.

Next time, some words about Astrobin, where I've started posting images. There's not much else to talk about thanks to the clouds and cold weather.

Sunday, January 20, 2013

Another Retirement Location Off the List

Dang, another place I was considering for retirement is off the list. See the big patch of brightness north of Dickinson, North Dakota?

North Dakota at Night

(This is a portion of a NASA Earth At Night image)

The light is coming mainly from the lights on the instrastructure supporting the oil production there. Media reports suggest that this light is mainly from the flaring of natural gas produced by fracking, but the people who fly the satellite suggest that's not the case. Here's a closeup of the field, from an image at the same source:

Bakken Field closeup
I wonder if the effect on viewing is as pronounced as it appears to be in these images? I don't know anyone who lives in that area to ask.

At one point I thought it might be nice to retire to someplace like Watford City and do astronomy outreach at the North Unit of Teddy Roosevelt N.P., and also do some dark-sky imaging too, of course.

The annual North Dakota Badlands Star Party is held at TRNP North Unit, so maybe when they post their dates for 2013 I'll ask about how the light has affected viewing.

Saturday, January 19, 2013

DIY Concrete Pier for a medium-sized SCT

What do you need for imaging with a Celestron 9 1/4" SCT operating at f/10 (FL 2350mm)? A mount with very little flex. In my case this works out to a Celestron CGEM mount. For a couple of years* now I've been working toward building a small observatory. I want to put the mount on a pier, and miracle of miracles I have actually gotten this part of the observatory done! Not without a lot of dithering about what sort of pier to install.

If you go to Cloudy Nights you'll see many people giving their ideas of what constitutes an adequate pier for imaging at a modestly long focal length. The largest telescope I anticipated using was a 9" SCT, so I felt much of the advice, though sound, was meant for larger loads. On the other hand, I decided that some suggestions were a little on the light side.

Some ideas I considered and rejected were for a pier made from 4x4" wood beams (possible polar realignment needed as the humidity changes), steel pipe piers (expensive), 10 or 12" concrete piers (overkill), 4-6" concrete piers (too much flex).

That left me with an 8" concrete pier as the ideal compromise. Cheap in cost, and easy to put together--even for me.

  1. Digging things, such as a hole auger and shovel
  2. A little small gravel to line the hole bottom
  3. Concrete forms
  4. Duct tape
  5. 2x4" lumber for holding the form level
  6. Bagged Concrete (Quikrete, for example) 
  7. Rebar
  8. Pier to mount adapter
  9. "J" bolts with hardware to match adapter
  10. Mixing tub such an old wheelbarrow
  11. Garden hoe for mixing concrete
  12. Bucket to measure water
  13. Water
Now, some lessons learned as applies to each of the above:

The frost line here is 42" down, so the hole must be at least that deep plus a few inches. Fortunately I had an old post hole manual auger that made digging a snap. It looks like this one, which can still be found for sale various places:

Manual Auger
Mine is actually an antique hand-me-down with a decayed wooden hand bar and several layers of rust on the metal parts, but it sliced into my mix of clay and gravel almost like the proverbial warm knife in butter. The only trouble I had was at 42" depth, where it ran into a larger rock (which now sits on a counter in front of me). The hole was deepened to 45" by using a long-handled shovel.

You just need enough gravel to put a few inches in the bottom of the hole for drainage. Pack it down with a 2x4".

Forms are usually available in 4 foot lengths (mine came from Home Depot). Because the total length of my pier was longer than this, I joined two forms by making a 1 foot long external sleeve and putting it all together with duct tape. The length is critical because the adapter will ride atop the form, which will be filled with cement to just below the top of the form. You need to plan things out so that the distance between the adapter bottom and the top of the cement is about 1.5" or so.

The form should fit nicely into the hole with a little wiggle room around it; level it and shore it up with 2x4"s:

Concrete form in place
Then I filled in the gap around the tube with the extracted dirt.  You can use the rebar to get that dirt packed in, and run some water into it to flush it down. (Don't add water unless you're ready to pour concrete; a wet form can lose its integrity in 24 hours).

You will need to know how much concrete to have on hand, calculated from the volume of the pier and the bag weight you're willing to handle. I was able to handle 60 pound bags, but smaller bags will spare you a possible blown back. I would suggest rounding up the amount you need by one bag, just in case. 

This is the fun part. You want everything ready before beginning, so cut the rebar to the right length (an inch or two shorter than the pier. I used one piece of rebar, centered in the pier, but some will say use three. Whatever your choice, make sure the rebar won't interfere with the J bolts.

You have, of course, already determined North, so that you know the way to orient the adapter!

Put together the pier adapter and J bolts so that the assembly is ready to put into the concrete. I used three 1/2" diameter 8" long J bolts (Home Depot) and the Starizona CGEM adapter. In my case the Adapter's diameter was smaller than that of the form tube, so I used shims to hold it in position and maintain reasonable level:

Pier Adapter in place with shims (after has been cement poured)
Now get your bags of quick-mix concrete, mixing tub, mixing tool, and water supply ready at hand. 

Note: Even if you're not using Quick-set concrete  you shouldn't let much time pass between one batch and the next. You won't take any breaks until you've embedded the adapter in the pier top. 

Dump a bag of concrete into the tub, add the manufacturer's suggested amount of water, and mix thoroughly. The common mistake (I've read) is to make the mix too wet, so try not to be tempted into adding more water. In my case I tried to avoid this error so diligently that I made the mix a little dry, but it seems to have worked out. Shovel the concrete into the form, minding the level.

After adding a second bag of concrete push the rebar into the poured concrete so that it's a the right height. You may need to hammer it to the right depth.  

Continue adding more batches of concrete, making sure your rebar remains centered in the form. You may also want to use a long rod from time to time to remove any trapped air pockets that form. When I made my pier I noticed that these pockets tended to form against the inside of the form.

The last batch of concrete should be large enough to complete the pier. Depending on the size of the shim(s), you will fill the form to about an 1.5" from the top. If needed mix in more concrete mix and water. You may want to make the last batch of concrete a little wet so that the J bolts will embed more completely. Shovel this into the form to the level you want and then push the adapter assembly into it. Make sure you have the adapter oriented to north correctly! Level the adapter and you're done!

Clean up your tools and the work site, then take a break. After 24 hours you can rip the form away. At this point inspect the J bolts to make sure they're solid--no wiggling allowed. If they're not, you have a problem. Post a comment if you do and I'll reply how I fixed this when it happened to me. 

Avoid the temptation to put a load on the adapter for at least several days (two weeks would be even better). If the weather is hot and sunny, moisten  the outside of the concrete from time to time and wrap it in plastic.

After a month you can apply a concrete sealer and paint the pier with an outdoor house paint. I went with white, but if fluorescent green is your thing, go for it.


*Why a couple of years on the observatory? The winter of 2011-2012 was so mild here that I found I hardly needed an observatory. And I was so busy during the summer and fall of 2012 that my talent of procrastination bloomed fully. Maybe next summer I'll get to it?


UPDATE, SPRING 2016: Still no observatory. There still seems little need for one; I'm doing more imaging at dark sites as the light pollution, neighbors' absurd "security" lights, and tree blockage all continue to increase. The wood planks on the platform have warped, but the pier continues to serve me well. Factoid: this blog entry is far and away the most viewed of all my posts (which isn't saying much).

Sunday, January 13, 2013

Another Year, Another M42

I've imaged good old M42 a couple of times in the past with my DSLR and ST80. This is a more ambitious try, using my ST8300 monochrome CCD and AT72ED:

M42 (click for full size)
What's ambitious is that it's my first serious attempt at an LRGB image where I've given some thought about how to properly combine luminance and color data. This could definitely use a longer integration time--it was only about 15 minutes per channel at f/6, made worse by fairly substantial light pollution.

Notice those spikes coming out of the brighter stars? They're from overhead power lines!

The next clear night I'll try taking some shorter exposures so that I can mask in the overexposed center of the nebula.

Coming shortly will be a report on the Orion 50mm mini-guider. I will be using it for autoguiding on scopes of different focal lengths. It cuts about five pounds off my mount's load by replacing my ST80, which weighs about 6.4 pounds when guiding. This is particularly significant because that 6.4 pounds rides piggyback on my telescopes and has a substantial moment arm.

Friday, January 4, 2013

Are Baader filters Parfocal?

At a recent star party I made an offhand statement that I doubted that my narrowband filters were parfocal. That set me wondering if I was correct and how would I go about determining this for all my filters. So I did a little experimenting one night by imaging Betelgeuse through all my filters.

I decided to set focus with the luminosity filter in place, and then cycle through all my filters seeing if the focus changed. Sorry, but I don't have a focuser with a digital readout. To get some sense of any focal shift I put a Bahtinov mask on my scope and imaged the results. I used three stars of different spectral types (O, A, and M), just in case the results would be influenced by wavelength. (I was imaging through my TV-102, so I didn't expect to see any significant wavelength dependence.) Here is a test strip for Betelgeuse (click to see full scale image):

Betelgeuse imaged through various filter configurations with no adjustment of focus

I used 5 and 25 s exposures for the broadband and narrowband filters, respectively, and processed only using ImagesPlus digital development. It looks like the central spike produced by the mask moves little if at all as the filter is changed. As expected, the focus shifts significantly when changing to no filter in use. So how much shift is significant? Here is an image resulting from 1/12th turn of my fine-focus knob away from focus:

Appearance when defocused by about 0.3mm

This is approximately an adjustment of 0.3 mm in focus and the central Bahtinov spike has shifted quite a bit. From past imaging experience, I think my final focusing "tweaks" are about 1/5 of this in magnitude.

So are the filters (Baader LRGB and 7 to 8.5 nm Ha/S-II/O-III) parfocal? They look close to being so. To my surprise, the broadband and narrowband filter sets seem to be almost, but not quite, parfocal with each other. The results were the same for the other two stars, Sirius and Altinak. But I'll probably still refocus every time I change filters in the future, particularly when using anything less than an apochromatic telescope or there's been a change in temperature.

Wednesday, January 2, 2013

Photoshop Actions

I spent a little (emphasis on little) of my holiday money on the purchase of two Photoshop action packages for astrophotography. My simple goal for today was using the packages to reprocess one of my old images. Here's my original take on NGC 6781, a small planetary in Aquila. This was shot in June 2012 using H alpha and OIII narrowband filters with my ST8300M CCD and C925. This was my original "final" image:

Original Processing

I used the OIII data for both the blue and green channels, which produced a washed-out cyan in the nebula's interior. Other defects in this image include some uncorrected mild vignetting, a noisy background and almost colorless stars. Using the actions it was an easy task to generate a synthetic green channel, clean up the background, give the stars some color and pretty much obliterate the vignetting (without any flats). Wow! That's not bad for a day's work with new software. Here's the result:

Processed using actions

Not that it's perfect by any means. I think the background is too black and I've lost a lot of the dimmer stars. I'll take it as good enough for the first day of using the actions.

The two packages are Astronomy Tools ($21) and Annie's Astro Actions ($15).  There's some overlap between the packages, but they're so inexpensive that you can get both!