Michael A. Covington    Michael A. Covington, Ph.D.
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M31 (Andromeda Galaxy)
M31 (Andromeda Galaxy)
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Teaching a new dog old tricks:
astrophotography with a classic lens

By "teaching a new dog old tricks" I mean using a new (to me) lens to take pictures very much like pictures I've already taken, to evaluate the lens.

Here's M31 photographed much the same way as last time (scroll down), but at f/2.8 rather than f/4. Note that the star images are sharp all the way to the corners. That is what marks the Nikon 180/2.8 ED AI-S lens (introduced in 1981) as a great lens.

This particular lens has visible astigmatism at f/2.8, but this can be cancelled out by focusing carefully. I have learned to focus for maximum visibility of the faintest stars. That minimizes astigmatism but not chromatic aberration; the brightest stars have vivid red halos! Here's an enlarged section from a picture taken at f/2.8:

The astigmatism and the halos would probably never have been visible on film; they go away when I downsample the images by a factor of 4 or 5 to simulate the resolution of film. Modern digital sensors can detect flaws even in excellent lenses.

How do I put a telephoto lens on a telescope mount? If the lens has a tripod collar, it's easy (click here to see my Canon 300-mm lens in action), but this one doesn't; almost the entire barrel rotates when it focuses. So I support it with rings like this:

as advocated by Jerry Lodriguss. Note that the astrophotos above and below were taken with a Canon body using a lens adapter, and I have recently moved the front ring farther forward.


Yes, I still do astrophotography

This picture of the Andromeda Galaxy is actually a lens test. It's a stack of ten 2-minute exposures with a Canon 60Da at ISO 800, a lens mount adapter, and my Nikon 180-mm f/2.8 ED AI-S lens, which I bought a couple of years ago but have just had repaired by Camera Service Co., whom I recommend. (It had a sticky diaphragm.) I supported it on the AVX mount using a dovetail bar and two rings (click on the link and scroll down).

This is an excellent lens, but not a perfect one. Introduced in 1987, it raised the standard for long telephoto lens performance. Mine, however, shows slight astigmatism at f/2.8 (wide open), and slight chromatic aberration at f/4. These faults might have been very hard to detect with film, but digital sensors are about 5 times sharper. Even with film, I was troubled by chromatic aberration in the Olympus 180-mm f/2.8 lens I used to have; this one is much better.

I plan to use this lens regularly at f/4. It performs very well. Also, in the spring, after getting my book manuscript finished, I plan to have an "old-lens festival" in which I star-test my whole collection of lenses, some very old and undistinguished (like the Promaster 135/2.8 that normally does service as a paperweight on my desk). In my copious spare time, of course!


To my fellow Christians, about sexual harassment

Society's sudden concern about sexual harassment has given us an unprecedented opportunity to tell the world what we stand for, if we'll jump up and do the job.

Key point: Our morality is not a set of thou-shalt-nots, it's a set of values — that is, it's a conviction that certain things are valuable.

Sexual intimacy isn't dirty, it is valuable, so valuable that it is reserved for couples who have made a permanent commitment to each other. We call it marriage, and we don't mean a piece of paper that can be torn up by mutual consent in a quickie no-fault divorce. We mean a real commitment.

What we are really against is meaninglessness. People aren't objects from whom sexual pleasure is to be taken. They are human beings every bit as dignified as ourselves. Their feelings matter, and their immortal souls.

And our morality isn't "traditional morality" if by that you mean traditional hypocrisy and immorality and prudery. We need to say this very loudly. We don't want to go back to 1950. We want to go forward to the Kingdom of God.

Spread the word. Feel free to share links.

Good food returns to Covington Manor

Last night (December 8) marks a milestone: Melody and Sharon cooked an excellent dinner of baked salmon and vegetables. It may be the best salmon I've ever eaten.

Ever since Melody started having a lot of trouble walking (three years ago!) we have relied heavily on convenience foods, takeout, delivery, and eating out. Since she got up and about, three or four months ago, I have taken her out to dinner almost every night. (I don't mind having hundreds of dinner dates with my beloved, making up for lost time!) But now normal cooking has resumed. The food will be much better for us because it doesn't have calories secretly inserted by whatever stealth technology the restaurants employ.

Sears on the decline

Sears, Roebuck & Co. is not long for this world. In their Athens store, their tool department looks pitiful. If you need a saw blade, don't go there. The only items that are abundant are Christmas gift packages, which are mostly socket sets in a great variety of sizes.

Back in the 1960s and 1970s, the Sears tool department was an important part of every town. I enjoyed going to the Valdosta Sears regularly with my father around 1965; one day we met Captain Mercury (a children's TV personality), who was making a public appearance. More often I marvelled at the gadgetry. I remember once encountering a pillow block and wondering what kind of big machine it was for. I have, and use, a C-clamp that we bought there.

Valdosta's Sears moved from Brookwood Plaza to Valdosta Mall in the 1980s and will close next month. Athens' Sears has not been announced as closing, but we don't know how long it will last.

The Sears tool department had two cultural aspects that stand out. One was the policy of free replacement of any Craftsman hand tool that "fails to give satisfaction." I have brought them worn screwdrivers and pliers — regardless of who originally bought them when — and gotten free replacements on the spot.

The other was prolonged support of older products. You could get blades for saws that hadn't been sold for 20 years. My 1994 8-inch table saw came from Sears and was basically the last surviving member of a 1960s product line (all newer table saws are 10-inch). Until just a few months ago, 8-inch blades, rare elsewhere, remained abundant at Sears.

Current events

Atlanta has just had an unusual snowstorm; we haven't.

Bitcoin has had a wild run-up and is now fluctuating wildly, by 20% or more within hours. That makes it useless. Econ 101 tells us money is supposed to be a medium of exchange (for trading), a store of value (for saving), and a unit of account (for measuring and setting prices). By fluctuating wildly, Bitcoin is no use for any of these. And it is completely unbacked — "backed by the full faith and credit of nobody," as I express it.

When people become conviced the Bitcoin bubble is over, they will all want to take their money out at the same time; everyone will sell at once, and the price will come crashing down again.

And many of those fortunes never existed. Put $1000 in, watch it skyrocket to $150,000, watch it crash back down to $500, and take your money out. Where's the wealth?

North Korea is a small dictatorship with no allies. Naturally, it wants to be able to defend itself. Unfortunately, it has achieved nuclear weapons. I think the right way to deal with it is to avoid provoking accidental war, equip ourselves to intercept missiles if North Korea launches them, and wait for (and try to hasten) an internal collapse, as happened with the Soviet Union.

Above, note that Kim Jong-Un's rhetoric about the inevitability of war is the same as he has been spouting for a long time. Despite the impression given by some news media, these are not new threats.

Please note that these are my non-expert opinions, as a citizen. Although I work in defense analysis on another level, I have no training or inside information about strategies for dealing with North Korea.

How did Tycho Brahe polar-align the Great Equatorial Armillary? I'm about to dig into his writings to try to find out. It was one of the first precision equatorial mounts in history.


My fellow Americans!

Yesterday our President used Twitter to distribute three anti-Muslim propaganda videos from a fringe group in Britain. All three were quickly traced to their sources and found to have been misrepresented. The President's press office then said that it didn't matter whether they were real as long as they "start a conversation."

Today we had, from a former national security advisor, a confession of collusion between the Trump campaign and the Russians.

If I could say only one thing to my fellow Americans during the current political turmoil, it is this: You have to care about facts, even when facts are complicated. It's not enough to just take sides based on labels or blind loyalty.


On a happier note, today begins, I suppose, my study of the Chinese language. I don't plan to go very far with it, but it's involved in one of my projects, so I might as well start dabbling. Chinese is a language in which vocabulary takes you a long way; there are no verb or noun systems to learn as in French or Latin.

The characters you see above are pronounced Zhōngwén and mean, literally, "central language." China calls itself 中 ("middle") because it's the middle of the known world (if you're Chinese).

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