Category Archives: Construction

Zenith Table complete

Except for a final coat or two of paint, the PZT (Pod Zenith Table) is complete. Now, in addition to the usual rotation, the dome can be pushed backward, entirely off of the observatory base. This opens up the whole sky, allowing the scope to look straight up, and eliminating the need to move the dome opening around as targets move.  I probably won’t use it all the time – no need for shorter sessions targeting just one part of the sky. But it will make more sky available, and will make things like automated TPoint data collection easier.

I’ve opened it for practice in daylight, but haven’t used it under dark skies yet.

Two Big Changes underway

Two things are in progress for the observatory:

  1. A new Right Ascension worm block. It has arrived from Bisque and I’ve installed it, but haven’t yet had a clear night to re-do PE measurements and see what effect it’s had.
  2. A PZT (Pod Zenith Table) – a DIY project, supported by hardware and plans sold by SkyShed, that allows the clamshell dome roof to be rolled off to the side.  Doing so will open up the whole sky above the dome – where, right now, I can’t point straight up or, indeed any higher than about 70° altitude.  Considering how high my horizons are (hedge, house), opening up the sky above will make a huge difference.  The PZT woodwork is assembled and I’m in the process of painting;  installation in the next few days.

Mount tune-up Journal 1: July 13

First step in the plan is the removal of my added-in through-mount cabling.  I opened the access hatch and carefully removed:

  • USB cable to the QSI camera
  • Power cable to the QSI camera
  • RJ-11 cable to the focuser motor

The other cables in there were installed by the manufacturer and I assume they’re OK.  My added-in cables were tangled, and I could easily imagine that they were contributing to drag.

I started re-cabling the mount with external cables run along the outside, and held in place by velcro straps.  However, I didn’t finish the job, as I was driven indoors by mosquitoes.  I’ll finish this job on the next available night.

PEC, Autoguiding stars, and a test image of M81/82.

It was clear last night, quite warm, although seeing and transparency were poor. More testing and calibration, and some real progress was achieved.

Better PEC

Now that I have focus perfect, and given my suspicion that I may be doing unguided imaging with this short refractor, I decided to re-do my PEC calibration. This time I used the main camera to get cooling and higher resolution. I captured about six worm cycles of data and recalculated the model.

Gathering data like this can be done before it is completely dark, so it was a good way to spend the hour of dusk while waiting for the sky to become completely dark. In the process, I noted two important things:

  1. Somehow, my TPoint model is off, even though it was near-perfect the other night. I needed to use a closed-loop slew to get to what should have been easy targets. I imagine I bumped something the other night while I was disconnecting and reconnecting the guide camera multiple times. Next testing evening, I will first try doing a re-synchronization and then, if necessary, a completely new TPoint model.
  2. SV80S-Field-CurvatureAlso, in the process of doing full-frame images with the large QSI camera, I can clearly see the field curvature. The extreme edges of the field are badly distorted, confirming this as the likely cause of the distorted stars I’m seeing in the guide camera, which is even farther from the center of the field.

So, I think I’m not going to worry about correcting those guide camera stars now, but, rather, see what I can do with unguided imaging. After all, this is a very stable mount, and I’m presently using a very short focal-length imaging scope.

Testing Unguided Imaging Limits

So, I slewed to a nice test image – a spot midway between M81 and M82 – and took test images at 10, 60, 100, 200, 300, 400, 500, and 600 seconds, with PEC on but no guiding. Those images, calibrated, are here:

Ignore the badly distorted stars at the upper left edge of the field, and look at the center. While I think I may have a minor collimation issue with the camera, I can see no difference between the stars in the 10-second image and those in the 10-minute image. With this mount and scope, I clearly don’t need Autoguiding for exposures in the 5-10 minute range. So, I’m going to shelf my calibration of the Autoguider until later in the season when I switch back to a longer focal-length imaging scope.

It also occurs to me that I have a field flattener for short scopes in a drawer somewhere.  If I come back to serious imaging with this scope later in the season (which I might want to do for a very wide field shot, such as M31) I’ll try that flattener.

Now, since I have a nice image framed anyway, I thought I would do some trial imaging of that M81 – M82 shot. I took 10 five-minute sub-exposures, unguided, and then a series of flat fields using the light panel mounted in the observatory. I already have a calibrated dark frame for use with this camera.

There sure are a lot of satellites in that part of the sky.  Lots of satellite trails to be removed.  Fortunately, the data rejection procedures in CCDStack make that fairly easy.

2015-04-17-M81-82-monoHere is the result, calibrated, combined, and cropped. (Still just a test – not a finished product, which would need better noise removal, scaling, etc.)

I would not have imagined I could get results like this unguided. This truly is a wonderful mount.

Static Electricity

A final note.  I’ve had several major static electricity shocks over the last couple of days, and I don’t remember this being a big issue in the past.  Twice tonight, a piece of equipment actually reset after a static spark.

What’s changed?  I think the answer is the new vinyl cover on the dome – I used to have a woven polyethylene cover, but switched to this vinyl one last year.  Maybe dragging the vinyl cover off the plastic dome is generating the charge.  Running a ground wire to the dome is now on the to-do list.

Re-installing, re-assembling mount

IMG_0751The updated mount arrived a couple of weeks ago, and I’m in the process of re-installing.  Since everything was taken off, I’m taking this opportunity to put everything back on in the neatest fashion I can – paying more attention to cable management, etc.

I’ve reached the point where I’m ready to start polar alignment – just waiting for a clear night.  Initial alignment will be done with PEMPRO, followed by a detailed TPOINT alignment analysis.  It’ll take a couple of clear nights. Tonight was supposed to be one – but the sky is thinly overcast, with the overcast lit up by a bright moon.  I’m hoping it will clear a little later in the evening.

Update: It didn’t.  Going on a week now, still waiting for a clear night for alignment. Frustrating knowing that even when it eventually clears, I’m not ready for imaging.  Oh well.  Remember, the hobby is the process not the results.

Pier Top Panorama

I have the new pier-top adaptor fixed up and ready to mount, so today I remounted the top plate.

Since the new mount hasn’t arrived yet, I thought I would take this opportunity to carefully take a panoramic photo from the telescope’s perspective, with the goal of installing a custom panorama into TheSkyX, to help plan and preview observing against a realistic simulation of what my very cluttered horizon looks like.

_DSD8221So, I temporarily mounted a tripod column on the pier top plate, with a ball head on top of that.  This places a camera at the same height where the telescope would normally sit, and the “pan-rotation” direction of the ball-head allowed me to take a bunch of carefully-aimed pictures.

I took a series of pictures (trying different focal lengths with a wide-angle zoom lens), being careful that they overlapped by about 30%. Here’s a sample (but many more were needed to get 360-degree coverage):

Then I used Lightroom and Photoshop to merge them into 360-degree panoramas. Since I took several different sets of input photos with different focal lengths, and with some with the camera oriented horizontally and others with the camera oriented vertically, I ended up with several panoramas of different quality (different kinds of distortion etc).

Taking the least-distorted, I adjusted it to be exactly 360-degrees, trimmed it to the size required by TheSkyX (which requires that both dimensions be multiples of 512), and set the sky area to transparent. The result looks like this:

EWHO-Pan-Port-24-05-transparencyI was able to load this panorama into TheSkyX so it shows up as the horizon on the star chart. This is a great feature of TheSkyX – I get the calculated sky chart overlaid on my actual horizon, so I can accurately see what is visible above the hedge, between the trees, etc.



Waiting for mount, re-doing pier top

The observatory is temporarily off the air while the mount is being updated.  While waiting for gear to arrive, I’ve taken the opportunity to do a long-overdue tidy-up.

  • Removed all the optical and electronic gear from the mount and pier;
  • Took the mounting plate off the top of the pier, brought it indoors, cleaned it, removed old tape residue, drilled for a new pier-to-mount adapter plate, and repainted it after steel-wooling it clean and smooth.
  • Cleaned years worth of junk out of the observatory, especially all the old packing material and other bits of junk that have accumulated in corners.
  • Vacuumed years of dead bugs out of corners (creepy).

According to the original schedule, I should have the mount in a couple of weeks, so that should be in time to re-attach, re-calibrate, and get some good use out of it while the dark season remains.

PC Cabinet Interior Heater Installed

As mentioned in a previous blog entry, I’ve been trying to arrange that the observatory PC can remain outdoors in our frigid winter temperatures and still start reliably when I need it. The problem has been the hard drive – at sub-zero temperatures it won’t start, and the PC fails to boot. I tried replacing the mechnical hard drive with a solid-state unit and, while this solved the temperature problem, it created other problems, and I returned to a mechanical drive.

Before-Heater-ChartHeating just the interior of the observatory with a heater designed to keep things just above freezing wasn’t a solution. When the ambient temperature dropped below about -15°, the heater couldn’t keep up and the pocket of air in the bay where the computer sits was still about -5°, too cold for the computer.

The deep dip on this graph was an observing run with the interior heater switched off (once the PC is running, its internal heat keeps it healthy). But you can see that the temperature was sitting at -5 to -8, even with a “no freeze” space heater running in the observatory. (Outdoor temperature was about -20 at the time.)

So, I decided to try installing a small, low-power heater inside the cabinet of the PC, with a thermostat to keep the cabinet interior just above freezing. Continue reading

-20 is quite cold, actually

Last night was the first clear night in over a month (that I was was available), so I spent it doing some imaging. The 3/4 moon was too bright for anything serious, but it was OK to work on adjusting autoguiding parameters.

It was about -20C. That’s cold. The PC wouldn’t start, so I think I am officially off the air in the cold until those enclosure heaters arrive. The LCD monitor also faded to near-invisibility, and I’m thinking I may need to apply a heater of some kind to it too.  I eventually got the PC going by leaving it powered on with the “can’t find hard drive” message on the screen, until the internal power consumption heated the interior somewhat.

Then I found I was getting strange effects with autoguiding, with the Declination guiding adjustments moving four times more slowly than the RA. I suspect a problem with backlash or stiction in the Declination gear. I did a bit of data gathering to better quantify some of the effects, but I wasn’t having fun in the cold, and called it a night after a couple of hours. I’ll have a look at the Declination gears and backlash during the day on a coming weekend (in a thoroughly-heated dome).

Once I get the heaters working and the declination adjusted I think it will be practical to do some basic image acquisition in extreme cold, but it’s not fun to be trying to do adjustments in those conditions.