The Starry Night, 25

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9/29/2010: Working up last night's M13 data. Globular clusters hypnotize me. The view of M3 in the 26-inch Clark refractor at UVa in Charlottesville, Virginia; M22 in a 17.5-inch dobsonian at the Texas Star Party; M3 (again) in the 25-inch Obsession at Chaco Canyon: I'm forever trying to reproduce and share those visual experiences. Fortunately, a sharp refractor, a CCD camera, and a good mount seem adequate. What is missing is technique. Working on it.

Tonight, I aligned on the pole with reasonable care, focused using the triangular mask recommended by both SBIG and Ron Wodaski, and then ran a series of 100 second exposures: 10 captures each in luminance, red, green, and blue. The R, G, and B images seem significantly sharper, so the photo below does not use the luminance data:


Click the image for a bigger view and to see more technical details.

As it happens, clouds moved in over the course of this session, so the red filter (the last used) saw significantly less light than the green, which saw less than the blue. That made getting a good color balance challenging, maybe impossible. I tried assigning custom weights to the channels in Maxim DL5 and continued tweaking the image in Photoshop until the background was some semblance of neutral and the stars of M13 approximately white. Brilliant supergiants add subtle color to these clusters, and their contribution is almost entirely lost in this data. Pushing the starved red channel any harder makes a mess of other aspects of the photo. The little galaxy in the lower right, familiar to observers of M13, deserves some attention during image preparation. Much of its subtle outer structure is visible in the raw data and should be better preserved in the final image.

For next time: use the fine focus tool in Nebulosity (focus was just a little soft in this image). Note that a Bahtinov mask from Farpoint via Agena is only $20 shipped. I don't see much reason to use longer subframes with M13. 100-second subs work well to prevent the core from burning out, and they do not require guiding with the A-P mount. Sooner or later, I'm going to have to work out a couple of guiding schemes (again) and make them routine. That won't happen until late October or November because I have a lot of earthbound stuff to deal with for the next few weeks.


10/30/2010: I replaced the desiccant plug in the ST2000XM with a Particle Wave Technologies kit. I should probably have waited a few months in order to exploit and enjoy the newly recharged OEM desiccant, but curiousity about how the kit worked (and the fear that I might lose it before it was actually needed) inspired me to go ahead and install it immediately. The extra pieces, instructions, and tool are all stored behind the egg-carton foam on the top of the ST2000's Pelican case.

Speaking of foam, I removed the foam from the dark blue original case for the A-P refractor. It had the consistency of sponge cake. It felt moist and fell apart under little more than a glance. This case was made in 1986, so I suppose I should not be surprised that the foam had totally broken down. Absent the foam, the 5-inch just fits with its rings attached. A little clean-up, a couple of braces on the bottom, some polyurethane, and I'll have a traveling case for the A-P. So, it looks as if I have been blindsided by a project that needs doing before I leave for TN on Monday. Not quite a week later, we leave for the Bluiffs Lodge in Doughton State Park, where I have long wanted to do some stargazing.

I've sanded and polyurethaned the interior tonight. Tomorrow I'll cut some wood and either dry fit it or glue and screw it together.

Addendum 10/10/01: Looky! That worked out well. Sea trials in Tennessee and Doughton Park over the next couple of weeks:


A bit of oiled cherry leftover from the dulcimer project and some scrap foam from this and that made all the difference. The bare case neatly holds the A-P in its rings, with dew shield. The telecompressor is retracted into the focuser body; the 35mm Panoptic, 12mm and 16mm Naglers, a Maxbright diagonal, and a 2-inch extension are all packed into the endzone. If I opted to use the flexible dewshield, I could put a similar foam insert at the other end of the case. I have ideas about how to do that in "convertible" form so I can waffle all I want when packing the telescope. There's no room for the bracketry for the guiding kit which will have to travel with the guidescope (duh) when needed.


Straightening up the office, I moved a box of astronomical sundries to the workshop downstairs: focusers, finders, rings, and the 4-inch F6 achromat I bought with the idea of supercharging the solar telescope. I think I will use it as a guidescope instead. It should offer a log((100/80) ^ 2)/ (log (100^0.2)) = 0.48 mag advantage over the Orion ST80. Worthwhile? Maybe. That's roughly twice as many potential guidestars. It's stored with a bunch of PVC fittings; needs something for a dew shield, and could use a bushing to mate the OEM ST80's focuser to the PVC. Flocking paper that used to be stored in the A-P case is airing out in the workshop, too. Get the tube length right, make the bushing, then flock the tube. No hurry, unlike the case.

Be on the lookout for a table wtih adjustable legs so I can have a level "office" for Tom Swift's Telescopic Suitcase. Some telescoping tubing and a few cotter pins would be a good start. This just won't do in the long run:




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                   © 2010, David Cortner