Michael A. Covington    Michael A. Covington, Ph.D.
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AVX declination axis freezes
Telescope dovetail safety screw extender

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What politics should and should not be

A recent Facebook posting of mine...

Politics ought to be the careful consideration of facts and values in order to make wise decisions about how to run the government.

For many Americans, for the past 2 years or so, politics has not been like that. It has mostly been about passing around pictures with slogans on them ("memes") or even false facts ("Congressmen get $174k for life"), through the gossip mill, without fact-checking or deep thought.

Either that has died down, or I've unfriended all the people who do it, I can't tell which.

We now know that a lot of that gossip was being fed to us by Russian propagandists. I urge everyone to get away from gossip, slogans, and trash-talk, pay close attention to facts, and try to be wise. It's your civic duty.

Feel free to share this.

Not gone, not forgotten

I continue to neglect the Daily Notebook to devote more effort to revising Digital SLR Astrophotography and to consulting work, which is going very well. More news here in December.

And I'm again attempting to get a new laptop. Recall that in March, I briefly moved from my Lenovo Z570 (which was on its third keyboard and second touchpad and hard disk) to a Lenovo Z50, which was very similar. Unreliable Ethernet in the Z50 caused me to give up and return it.

Still, I like Lenovo, and now I have a Lenovo Ideapad 320. That means I'm moving up from a 15-inch to a 17-inch screen, as well as quad-core CPU. I've done a week of "soft start" where I use the new laptop regularly but have not moved the programs and data that can only be on one computer at a time. I'm writing this blog entry on the new laptop. So far so good...


Telescope dovetail safety screw extender

When it has a heavy camera on the back, my telescope needs to sit farther forward in the saddle than the rear safety screw will let it. So I devised an extender for the rear safety screw. Here you see how it's built and how it looks in use.

It need not be especially strong because it doesn't hold the telescope in the mount; it just keeps the telescope from sliding far enough that the saddle couldn't hold it. I used aluminum, but wood would do.


Thanksgiving Week

I'm devoting my available writing time to Digital SLR Astrophotography (second edition), not the Daily Notebook. But I do want to acknowledge Thanksgiving...

...and this year, we have many things to thank God for, among them:

  • After a year punctuated with medical crises, Melody continues to recuperate. She now does all her own driving. She still uses a walking stick (and, in large stores, a scooter; and when carrying things in the house, a rolling walker) but getting her strength back is just a matter of time. I am glad to have her back!
  • Sharon is also getting steadily healthier and was able to go to Atlanta to visit friends for a couple of days just now.
  • Cathy has a new job teaching art to beginners and is very happy with it.
  • The grandchildren are thriving, and in particular, Mary (almost 5) treats Emily (1) as her baby!

During Sharon's trip, Melody and I had a 2-day stay-at-home vacation, during which I did no work. It's very rare for me to go that long without working. I got some good rest.

Technical changes at Covington Innovations

A couple of weeks ago, we retired Pallas, the desktop computer we had been using as a file server since (I think) 2011. Its server functions were moved to my Dell quad-core desktop, Philothea, which was rechristened Pallas to simplify the network.

In the background of this is the fact that I've found the best way to run Linux is in VirtualBox under Windows. It has complete file and even clipboard interoperability. Unlike Bash for Windows, it has a GUI, and unlike a dual-boot system, it doesn't interfere with Windows (hence Pallas' server functions are not interrupted).

Decommissioning Pallas led to a rearrangement of the work area. We also decommissioned a color laser printer that had long ago ceased to print color properly. That made a lot of room. Minerva the Retrocomputer (which triple-boots Linux, Windows XP, and DOS with Windows 3.1) has moved to Melody's old desk, where Pallas was, and is now a working Windows XP system. For lack of PCI slots, it is Minerva, not the new Pallas, that has the Nikon Coolscan III slide and film scanner (whose SCSI card requires a slot). Our venerable old HP sheet-fed scanner is also on Minerva.

(The long-term plan here is to convert Melody's old office/studio into something more suited to our present needs. She retired from graphic design quite a while ago, and although the room will remain to some extent an art studio, she no longer needs a typesetting workstation or high-resolution printer. We can compact things just a bit.)

To move the Coolscan III to the new Pallas, I would have needed either a PCI Express SCSI card with the right connector, or a USB SCSI adapter. Either one would cost over $100. And the Coolscan III is due for an internal cleaning and lubrication fairly soon, probably within a couple of years. And it has a bit depth of only 10 (in film terms, D=3.0), which is just adequate.

But I happened to find a freshly serviced Coolscan IV on eBay. This is essentially the same machine, taking the same film holders, but attached by USB rather than SCSI. And its bit depth is 12, which is plenty for photographic film (D=3.6). Right now both Coolscans are in service, on different computers.

The Coolscans and flatbed scanners (Pallas also has a small one) are all are used with Vuescan (www.hamrick.com), rather than their own software; Vuescan supports all scanners regardless of operating system, and a single license is good for one user on more than one computer.

You can see where this was leading — Pallas needs more USB ports. But since this is the era of USB, Pallas is rather short of internal slots. It has one full PCI slot (occupied by the graphics card I added) and one PCIe slot. So I bought a quad USB-3 adapter for the PCIe slot...

...and I put it in and it works, but it still wants an additional power connection (through a SATA power cable) to be able to deliver fully rated 5-volt power to USB devices. This is not an urgent need — it's a desktop, and the USB devices around it are mostly self-powered — but I want to do things properly, and for that purpose I had to order a SATA power cable splitter, which will be here Wednesday.

Meanwhile, Pallas (without hard disk), the old HP CP1518ni color printer, and sundry other pieces of computer hardware went to Free IT Athens, which refurbishes old computers and sells them very cheaply to people who can't afford new ones. This is going to continue.

And yes, this entry is very much like the late Jerry Pournelle's "Notes from Chaos Manor." May his memory be eternal.


Celestron AVX declination axis freezes
when installing saddle or at other times

Major revision, February 2019

Introduction: There are a couple of reasons the declination axis of the Celestron AVX mount may be too stiff or completely freeze up. (It is supposed to be stiffer than other mounts, but not extremely so.) If it freezes only when you tighten the counterweight bar lock nut, then skip to Step 4 below. Otherwise start at the beginning of my story.


The other day I installed an ADM dual saddle on my Celestron Advanced VX (AVX) equatorial mount and encountered a strange symptom: When I fully tightened the 4 screws under the saddle, the declination axis became extremely stiff or completely unmovable. Normally it is supposed to be about 2 to 3 times as stiff as that of a CGEM because it doesn't have the same type of bearings. But not frozen stiff!

First I checked the plastic ring that serves as a bearing at the top of the declination axis (to keep the saddle, which moves, from contacting the outer casting, which doesn't). It was there, doing its job. See Don Halter's posting on Cloudy Nights; he had the same problem and attributed it to excessive thickness of the plastic ring. In his case, removing the plastic ring cured it. Not in mine.

But then I thought about it a while. What if the essence of the problem is that the whole declination axis is sitting a bit too low in the outer casting? By "low" I mean "away from the saddle." Then tightening down the saddle would compress the plastic ring and keep it from working properly as a bearing.

I flipped the mount head upside down, removed the counterweight bar, and had a look. There, a retaining ring (tensioner) holds the declination axis in place. The retaining ring is secured to the declination axis by two set screws so that you can tighten it just enough and then lock it in place.

Well, it was too tight. The set screws had come loose, allowing the retaining ring to rotate freely. Then, whenever I tightened the counterweight bar lock, I was also tightening the retaining ring. Miraculously, I didn't tighten it enough to make the mount freeze — until I replaced the saddle and took up all the slack at the other end of the axis.


Step 1: Make sure both set screws are loose (mine already were). There are two, opposite each other. Use a 1.5-mm hex wrench.

Step 2: Loosen the retaining ring, then re-tighten it moderately tight, not super-tight.

Step 3: Re-tighten the set screws, good and tight. They have a job to do.

Note: Tighten them equally, or you can pull the axis off center. If the declination axis becomes stiffer as you tighten the set screws, you've put one of them farther in than the other.

Step 4: Add washers so that the counterweight bar lock nut (big black nut) cannot apply torque to the retaining ring or bind against the mount housing.

The solution that I'm presenting here was devised by user "wcoastsands" on the Cloudy Nights Forum. The photos are my own and are more or less self-explanatory:




I should emphasize that all this probably depends on how your declination axis is adjusted, so that many of them have no problems, although it is not good that the big black lock nut can turn the retaining ring.

The washers you need are 16 mm (5/8 inch) in the center, no more than 26 mm (1 inch) in outside diameter, and a total of 3 mm thick (for my mount; yours may differ). I used two of the following spacer bushing, which I got from Home Depot:


Here's an Amazon link for the same item. Another suitable washer is known as an M16 oil drain gasket and is used on the oil drain of a few cars and motorcycles, but it's an uncommon size.

The thickness that I needed was more than one washer could provide, so I stacked two. You can glue the washers in place using contact cement if you remove your counterweight bar often and are afraid of losing them.

In 2017 I published a less satisfactory solution that used a lubricated washer to keep the big black nut from tightening the retaining ring. Here are my pictures from then:

Addendum: When the retaining ring at the bottom of the declination axis is adjusted correctly, the plastic ring at the top, just under the saddle, is not load-bearing at all. It is maybe 0.1 mm lower than the inner, revolving declination axis.

The dimensions I measured for the plastic ring are: o.d. 75 mm (maximum), i.d. 62 mm (minimum), thickness about 0.7 mm, not critical, as thin as practical (and adjust the retaining ring after replacing it).


Please pardon my absence...

Nothing is wrong, but I'm busy writing the second edition of Digital SLR Astrophotography, and doing other important work, rather than writing Notebook entries.

An intelligence test

Here is something I posted on Facebook several days before the Texas massacre, all the more relevant in the discussions that are now necessary.

Why is it so impossible for some people to rationally consider the following two things at once?

(1) Guns don't kill people by themselves; people kill people.

(2) Guns, especially certain types of guns, make it appreciably easier for people to kill people.

Plenty of people, both those who want to decrease gun control and those who want to increase it, do understand both points. From there it's a matter of gathering facts about where the main hazards lie and how to mitigate them. I can have worthwhile conversations with everyone in that set.

But I have been running into people who find it just impossible to consider items (1) and (2) at the same time. It's as if I were asking them to calculate a 4-dimensional matrix rotation in their heads. They get angry and spout illogical nonsense.

Or else they feel they are forbidden to admit that one of them is true (usually the second one), that if they do, they're surrendering to the opposing side, as if logic were a war or a football game, where if there are two propositions, they cannot both be true; one has to win and the other has to lose.

A related point: Annoyingly, some people wade into any discussion of gun control and start railing loudly against some unreasonable position that no one there has actually advocated. Why? To save themselves the trouble of listening and reasoning?

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