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12/10/2010. I downloaded a trial copy of CCD Inspector. And while I am not sure I am ready to fork over the money to register it, it is indeed an eye-opening and useful program. I mean, really: there's a small fortune's worth of gear out in the yard and this $180 package will take some of the guesswork out of efforts to make the most of it. I have 30 days to work things over and consider. This is going to get a little arcane if you're not into this stuff, so if you're cruising for pretty pix, scroll down rather than slogging through all these notes. I've been reviewing the last three months of images. First: That aluminum brace was a mistake. It addressed the rotation issue, but it introduced a lot of tilt. The rubber bands it replaced did not protect against rotation, but with them the field was square and well-centered. Providing relief by bending the aluminum brace helped reduce the tilt the brace introduced but did not eliminate it. After inspecting the curvature and alignment of the last three months of images, I gave in and removed the Mandel Wide Field Adapter for Nikon lenses, an adapter whose play had long troubled me. I restored the original CFW-8a faceplate and threaded a 2-inch A-P adapter into it. This seems rock solid. (If I ever do want to shoot with any of the Nikkor collection, it will take all of five minutes to put the Mandel WFA back on.) I remounted the CCD by means of the same spacer I machined for the telecompressed imaging train and tightened down the four set screws. The resulting extension is slightly less, so the cameraa reaches focus cranked out a little farther. The telecompressed A-P now operates at an effective FL of 557.4 mm, which provides an image scale of 2.73"/Pixel on the ST2000XM, and an f-ratio of F4.39 (compare: 543mm, 2.83", and F4.3). Checking the first images of the night, CCD Inspector confirms that things are much improved: optical and mechanical centers are off by only about 3 pixels; there is virtually no tilt. Under yet another unexpectedly clear sky, I took color data of the Iris Nebula then let the telescope take L data while Amy and I watched a movie ("X the Unknown") courtesy of Netflix. The sky hazed up; I may have nothing of use except for measurements. The measurements are not reassuring. Something is still out of control with alignment. The color frames are OK (just) but the subsequent L-frames are a mess. Did something slip? Did I neglect to tighten the focus brake? Where's the play? Rhetorical question: it's almost certainly in my homemade spacer.
12/11/2010. I removed the custom spacer (faceplate to insertion point: 3.25 inches) and replaced it with the all-purpose 0.8-inch Feathertouch fine-focus adapter. With the A-P 2-inch nosepiece, the minimum extension is 3.5 inches. This approximates the thickness of the Nikon Mount plus T-ring plus custom extension when used with the Mandel adapter. The sky is rapidly clouding over, so I doubt there will be stars to test with tonight. The day is too light to use reflections in a Christmas tree ornament as surrogate stars. A solar filter and 30 second exposures of Vega might work, but it didn't today. Either my aim or the focus or the haze defeated the effort. Try that again when fewer variables are in play. The Sun itself eventually served as a focus test. The white light solar filter plus the 10nm Schuler H-a plus some altostratus promising snow served to dim the Sun such that a 1 ms exposure showed the sun's limb and one big sunspot. Good news: yes, with the Feathertouch racked almost all the way in and the A-P focuser set so that the silver drawtube is just hidden, there is a good focal point. That's the war. Here's the battle: with this arrangement, using the Feathertouch changes the effective focal length, because it changes the seperation from telecompressor to sensor. That means that a) I can fine focus with the FT at the expense of slightly changing the image scale (how variable? don't know). Or b) I can lock the FT at some point within its range and focus using only the A-P focuser. That option will fix the image scale (making the Feathertouch "focuser" in effect a zoom knob with a range of something like 540-570mm). It's worth finding both the limits of useful focal lengths and the amount of FL change associated with the fine focus motion of the Feathertouch and then picking a strategy for any given night or subject. (Don't get too far out ahead of the game: it's also worth finding out if this combination of tubes and connectors holds the detector square.) Maybe the ideal method involves finding the shortest EFL that permits focusing in both H-a and white light with room to spare for temperature variations and standardizing on that setting. (D'oh! Rack the A-P all the way in, then focus the Feathertouch. If practical, that will guarantee both repeatability and the shortest avialble EFL.) If the change in FL does not interfere with image combinations or if the precision achieved warrants adding Registar to the software kit, then focus using the Feathertouch. If the changing image scale is a problem and it may be if it renders flat fields impractical, then focus with the A-P. The jury is out: is this a bug or is it a feature? Monday night (12/13) is supposed to be clear, but blustery. Stay tuned.
Commerical 24db parabolics have a beam spread (-3db) of 8 degrees. The entire cul de sac subtends about that from down here (60 feet wide, 500 feet away). I have no reason to think my homemade model is any tighter and plenty of reasons to think it is not as tight. Commerical models are said to offer useful signals at a mile or (much) more. I need a tenth of that. Aiming the beam into the center of the cul de sac should cover the cul de sac from side to side, and I can cheat the aim a little left or right depending on the best place to put the telescope for the chosen targets on any given night.
12/13/2010. The weather tonight is as promised: very windy, clear, and cold. I racked the A-P focuser all the way in then focussed entirely with the Feathertouch through the L filter. Focus is very repeatable, very matter-of-fact, utterly doubt- and drama-free. But perhaps the final image is no sharper. Who can tell with the wind above the pines blowing 40mph. Seeing is dreadful FWHM PSF's are upwards from 6 or 7 arc seconds!). I'm taking 300s L frames of NGC 7331 and vicinity. The first, twilit image should tell the tale. What's the EFL, and how flat is the field?
Essentially no tilt (3%), and mechanical
and optical axes differ by only 5.5 arcseconds. Before the night was over, I set the Feathertouch to its minimum extension and focused with the A-P focuser alone. That defines the maximum image scale with this setup. Not that I'll ever use it, but that data point lets me quantify how the focal length changes when tweaking focus with the Feathertouch, as I might do between filters or when the temperature changes enough to influence focus. So, what's the image scale with the FT racked all the way in?
That's not as much change as I feared. The full range is produced by 10 turns of the fine focus knob. The difference between L and H-a positions is about half a turn. [Next day: the measured FL with the H-a filter focused via the Feathertouch adapter is 538.5mm, a change of only 0.7mm.] The NGC 7331 images were dreadful: hardly any detail visible in the arms of 7331 and nothing but a smudge where the Quintet lurked. [The color data came in handy later; see below.] I again racked the A-P focuser all the way in, refocused with the FeatherTouch, and aimed at NGC 891 (just because I could). I started taking 900s L frames. Seeing remains very poor. The occasional gust moves the telescope just a bit. But the sky is clear and all the equipment is setup and working properly, so why not take data?
NGC 891, an edge
on galaxy in Andromeda
After 2 hours of luminosity and 45 minutes of color data of NGC 891, I sent the telescope to NGC 1499 for an H-a series while I caught some sleep. While watching the first frame or two come in on the desktop computer, I scored a Mandel "Muscle Plate" for the CFW-8a on Astromart from an amateur in Ontario. That will be one more potential source of flex removed from the imaging chain. If you're going to spend thousands of hours using this thing, for heavens' sake make sure it's set up properly.
Part of
NGC 1499, an emission nebula in Perseus
Reviewing the late-night take in CCD Inspector, you can clearly see that the star become more and more elongated until something turns loose in one frame and produces doubled stars. After that, the images are clean again. Tilt increases as the crisis point approaches, too. The guide camera kept doing its job, so something must be moving the CCD. I'm guessing cables are dragging. I rotated the camera 180° (d'oh!) so the power cable doesn't have to reach around it. If this doesn't do the trick, I'll move the power brick for the SBIG out of the under-telescope power bay and maybe add it to the tracking load. Between the doubled image and the field tracking below the eves of the house toward the end of the programmed sequence, I got 3h 45m of useful data. Tonight I'll shoot a similar region. That will give me a chance to check for interference, drag, and other misbehaviors at the same angles and might produce a nice photo into the bargain. Surprise! I saw exactly the same behavior as before, despite rotating the CCD to relieve cable strain. At the same angles, stars began to elongate, followed by a single frame with doubled stars, and then back to circular PSFs. This time, I was watching a graph of guider input during the crucial moments. I saw several full (rather than small fractional) pixel divergences and automated recoveries, but that's all. Nothing looked significant. Today I removed the 1.25-inch prism diagonal from the guiding chain (I needed it to take up backfocus when using the OEM focuser, to keep it from being too much extended; it was much less rigid than the GSO focuser I am using now). Even so, I took up backfocus using a 2-inch extension tube. At nightfall, just ahead of a heavy overcast, the vanguard of an icy storm system, I slipped in some focus tests. 21 images with the DSI of the Moon through the ST80 guide scope, averaged. The focuser needed only a small adjustment from its original extension.
Part of NGC 1499,
an emission nebula in Perseus
In addition to the trials detailed above with respect to image shift, I got another good shot of the California Nebula and a nice luminance frame of NGC 7331 and environs. This combined well with color data from a couple of nights ago. Tonight's color data was badly hurt by gradients, either from twilight or the brilliant moon.
NGC 7331, the Deelick Group, and
Stephen's Quintet: galaxies in Pegasus
These exposures were guided on the 10th magnitude star just above the Quintet using 2 second exposures with the DSI. With 10s exposures, I could see the Quintet and I am sure I could have guided on 13th magnitude stars! That's impressive sensitivity for an 80mm 'scope.
12/15/2010. To insure that the guider would focus when the DSI was mounted straight through, I took aim at the only celestial body visible in the quickly deteriorating sky. The Moon was heavily and variably obscured by rapidly moving, thick but broken clouds while I collected 20+ frames.
THe Moon in the straight-thru guide scope Humble as it is, that image demonstrates that the guider focuses straight through, that Nebulosity can see and record the DSI's output, and that the Linksys wi-fi range booster / repeater works just fine. The repeater is plugged in in the galleria at the moment. Out by the telescope, I had four and usually five bars of signal strength where I have previously enjoyed only two and sometimes just one. Remote access failed at first, but after I asked for a filelist using "my network places," Remote PC worked like a charm. All this bodes well for the parabolic antenna / cul de sac project. Following my Moon trials, I brought everything indoors hoping but not really expecting a) snow and b) to get it all back out again ahead of next week's total lunar eclipse. The repeater was only a little trouble to configure. I wired it to the router then logged in on its default IP and adjusted its parms (all I remember changing was the channel -- I use 11). After thus introducing it to my network, I saw a few warnings about IP conflicts, but I ignored them. I unplugged the repeater, unwired it, then plugged it back in. I held the sync button for a few seconds, got the double blue lights on top, then rebooted computers to insure that they all had fresh DHCP assignments. And hey! All is well. For $23 and free shipping, you get a nice piece of hardware, but zero documentation. Online remarks suggest that the documentation would have been worse than useless, so no harm done. You also get a CD marked "LOAD THIS FIRST!" which I ignored, also on online advice. It's still sealed.
12/16/2010. Incremental progress on several fronts. With the repeater on the front porch, the netbook connects for some distance up the driveway, a third of the way to the cul de sac and maybe a little further. So far, so good. But the first try with a parabolic reflector was neither a total flop nor a howling success. I had one bar in the cul de sac, but could not get a webpage to load. It was a pretty casual effort, with the repeater simply sitting on the porch and aimed through the woods as if they could be ignored. I need to experiment with antenna placement, aim, and so forth. I went over the guider and main OTA looking for sources of jitter, slack, play, etc. I found a few things to correct, and one or some of them might actually have been the culprit. Two of the three screws that hold the A-P lens cell in the tube had backed off enough to let the cell move. The top collimating bolt in the aft 3-point ring holding the guide telescope was binding prior to the point at which it exerted pressure on the guiding OTA (this is not likely an issue with the observed shift, since I lowered the guide scope in its rings to give me room to grip them as if they were handles after I brought everything inside and only then could this have come into play). The prism in the guide scope's star diagonal had just a touch of play; the diagonal has been removed. And I noted that if the clamp ring in the guide scope's GSO focuser is not really cinched down, whatever it holds can tilt around an axis drawn from that bolt to the opposite side of the adapter. Only the loose lens mount seemed to allow movement in both RA and Dec, so that one is my prime suspect. I've been looking at scripting Maxim DL for the upcoming lunar eclipse. I want something to drive the Canon 50D for the duration of the eclipse, bracketing widely every several seconds. I need to get this worked out just in case the weather cooperates, which does not seem at all likely.
The places from which a good signal is available are limited to the area right around the mailbox. These mid-December woods are about as thin as they will ever be. The spots this arrangement makes useful for the telescope offer much less eastern and southern sky than I want for the trouble it will take to use the kit in the cul de sac. A complete, all-season solution will need to be built from different pieces. Start composing "bridge to nowhere" and "a bridge too far" snark now. A business-surplused WET54G ethernet bridge is on its way from California (half the sale price from Amazon). I've measured the cable run (it's 150 feet shorter than the demonstrated wifi connection, about 400 feet from the edge of the woods to the edge of the cul de sac). I'll wait till the bridge has been tested before looking for lots of wire (CAT 5E?), a few plugs, and a crimping tool. For now, I am planning to use the repeater to get signal to the bridge, but depending on the sensitivity of the WET54G, I might be able to dedicate the repeater to the all-wireless backyard setup.
12/18/2010. Collimating an A-P refractor. What? Yeah, well, every frame from CCD Inspector insists that the detector is not perfectly square. And given that I did find that the lens cell had some play in the tube, there's no guarantee that I'd put it back in an optimal position. Until tonight. This evening I plugged a laser collimator into the Feathertouch and started working on having its reflection fall back on the laser aperture. Turns out that the lens cell did have a preference for which hole in the cell went with which hole in the tube. I added a couple of layers of paper tape on one side to snug things down where they belonged. The Feathertouch 2-inch adapter (which is held to the focuser body by three allen screws) could use a tiny bit of adjusting, too (eventually it may need a few thousandths of shimming). Comparing measurements and images, it looks to me as if CCD Inspector is more sensitive than it would ever need to be, but that's with the relatively small chip in the ST2000XM and with star images spilling across a few arcseconds owing to seeing and who knows what all. The same degree of tilt that is measurable but visibly harmless with this chip might be lethal with a full-frame sensor or an STX-class chip and tighter point spreads. Besides, when you're trying for the last little bit of sharp, every issue matters. I would love for the tilt I am measuring now to be the worst problem I had to solve. Someday it might be.
The state of the Universe. I really don't like things that don't work well, and the more things you own, the more things you own that don't work right. Given the technology-heavy nature of this sport, that seems a strange attitude. But look: the idea is to trim the kit down to just the things required to accomplish some task and then insure that those things work well, all the time. So I don't want seperate solutions for different parts of the sky, or seperate setups depending on whether I am doing tri-color or monochrome imaging. As much as possible, one outfit, one method, one set of techniques, one circle of experience should suffice. That circle must be big enough to encompass solar, lunar, planetary, and deep-sky photography in the backyard, up in the cul de sac, and on the road. To the extent that one needs to substitute optics and detectors, fine, but those are details. Expensive details, but details. The broad strokes for the whole program are simple: there's this precision mount which carries two telescopes. Both feed CCD cameras that connect to one computer. One CCD collects light for show and tell while the other informs the computer where the mount is pointing so the computer can tell the mount how to move in order to point where it's been told to point. All the communications effort is for my convenience: so that I don't have to stay beside the telescope to operate the computer attached to the cameras and the mount. If I can operate that computer remotely, I can operate the telescope remotely. Three scopes altogether: two for imaging and another for guiding, and one computer to control them all. If they all use the same control suite of software, then they're all the same outfit to me. We're not quite there, but we're close enough that the enterprise is comprehensible and becoming routine. It has come to the point that I don't have to spend all my time figuring out how to do things but can spend some of it on learning to do them well and some more on plotting and planning what to do. Now that it all clearly works and I am pretty sure I have a means of communicating with the kit whether I am standing beside it or sitting in my office, the next thing to take up is power when away from line current. I have the pieces, but putting them together in a reliable, repeatable, convenient form may prove a bit of a trick. Or maybe I'm being pessimistic and it will all work as expected, first time, every time.
12/19/2010. Tomorrow night: total eclipse of the Moon. I've been setting up hard- and software to try an ambitious time lapse. Until now it's been safely theoretical, 'cause the weather forecast has been pretty dismal. But the forecast has been trending better the last couple of days. The IR satellite imagery doesn't look hopeless to me. Now I'm thinking there's just a chance I'll actually see this eclipse. So maybe I should make really sure all the various -wares are playing together. |
12/12/2010. I've ordered a wifi repeater
with a view toward extending control over the telescope to the
cul de sac. The 
I messed with the parabolic reflector with
the wifi repeater some more, and I just can't seem to get a useful signal up
through the trees. I'll try shooting it straight up the driveway (which is
not all that straight) tomorrow and see if absorption by the trees, simple
distance, or aiming is stopping the show. If the trees are the problem, they
will be more so in any other season. An alternate plan is simple enough (once
you find the right lingo and device). It involves a Linksys WET54G wireless
bridge. Set
one of those out where I have a good signal either from the home wifi or the
repeater, run power to it. The WET54G will put the wifi signal on an ethernet
cable. Run the wire through the woods up to the edge of the cul de sac.
Terminate it in a generous coil in a weatherproof plastic bin to be deployed
or stored as needed. 500 feet of ethernet is beyond spec, but this is hardly
a demanding application. The wifi link at the foot of the run would isolate
the computer from lightning surges and keep me from having to punch a hole
for the cable through a wall or hang it out a window. If I place the repeater
a hundred feet up the driveway, I can trim that much off the cable run. Up
top, I can use the ethernet port on the netbook and turn off its internal wifi
for even better battery life. It can live inside a car for heat and frost and
dew protection or in a box on warmer nights. If I eventually need more connections
up top (for example, if I were to use two computers, one for the camera and
guiding duties as I use mine now, another for aiming and focuser control),
it will be a simple enough matter to provide an extra port (for example, a
DualComm USB-powered 5 port ethernet hub) or put another wireless bridge up
top (use a "Power
Over Ethernet adapter") and have a strong wifi signal in the cul de sac.
Or find a way to shoehorn more USB ports onto the one computer (supplying power
to a USB hub is not trivial).
12/17/2010. The parabolic antenna works!
And very well. I set the repeater on a lawn chair due south of the
house, 30
or 40 feet from the router. I lined up the repeater's antenna with a sight
hole drilled through the top of the parabolic reflector indicating its approximate
focus. I aimed the reflector up the driveway, intending to thread the
needle through the gentle S-curve the driveway makes through
the winter pines. Then I walked up the driveway
watching the signal strength on the netbook. Even a tree or two makes a big
difference; when the driveway bent a little south, the signal dropped two bars. At the top of the driveway, standing at
the edge of the cul de sac, I had four out
of five bars.
I started Firefox and surfed for a minute or two; I watched the trailer for
the Coen Brothers' "True Grit" which ran without a stutter. It all
worked like a charm. As
long as I could see the antenna. Walking to the middle of the cul de
sac dropped the signal to two bars. Walking north or south (which was both
out of the center of the beam and into the radio shadow of pines) dropped
it to two and sometimes to one bar.
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© 2010, David Cortner