Posts Made By: Alex McConahay

You heard the expression--

"Drone strike killed the #3 man in Al Qaeda four times last year."

We keep making the drones, and they keep getting new #3 men!!!

The beat goes on.

Alex

Assuming you are talking visual, a 6 inch Mak could fit on most heavy duty camera tripods, and these are much less expensive/lighter, etc. than astro stuff.

If you really want to get into astro gear, a CG5 (which shows up in many names) class of mount (LXD 55/75, super Polaris, etc.....) is a good bet.

Alex

There are those who like to have a specific eyepiece for every possible combination. There are others (like me) who say that, for any given scope, you need only three eyepieces.

With that in mind,

Get the highest quality you can afford
Consider buying used
Get the widest Apparent field of view you can afford (At least Plossl's (at 50 or so degrees), and 82 degree Naglers/Ultra-wide class if you can afford them)

Space them so that, when using a 2 power Barlow, you double your eyepiece set. (Don't, for instance have a 25, a 12 and a 6. Instead think 25/15/9. If you then use a Barlow doubler, you get 25/15/barlowed 25 or 12.5/9/Barlowed 15 or 7.5/Barlowed 9 or 4.5. (If you would have used a barlow on a 25/12/9, you would still have only a 25/12/9/4.5)

Consider exit pupil, and do not get anything larger than 7 mm exit pupil if you are young, or 5 if you are an old fart. Your eyes only get so big (depending on age) and having an exit pupil bigger than your eye generally wastes photons.

If you are talking a reflector with a central obstruction, don't get anything so long as the shadow of the central obstruction will show up.

Don't get an eyepiece that will result in a magnification of more than 250 or so power unless you have particularly good seeing. (The sky will not let you use it very often.)

Get one that gets you a high magnification, one in the middle, and one with the lowest magnification-- consistent with the restrictions on seeing and exit pupil mentioned above.

That is my advice.

Alex

I saw one up in Palmdale a couple of months back. An active one. Active enough that we were told not to look at it, and certainly not to allow it into any of our photographs.

Alex

Looks funny where you have the counterweight bar almost horizontal.....Reminds me of an eclipse trip to Panama a few years back and I could not understand why all the local astronomers were using their equatorial mounts in what seemed like alt-az. THen I realized that at the equator, that was kinda how it was!

Alex

You pretty much got it. If you buy an Ha filter to get 656.3 nanometer wave length, you get from 650.3 to 662.3, (roughly) if you buy a 12 nm bandpass filter. But with a 6 mm bandpass, you get 653.3 to 659.3. The light allowed to get through is centered on the target wavelength, but some slips by on either side. And we are talking a bell curve here, not precise cutoffs.

The narrower the bandpass, the more centered the light is centered on the desired band.

Does it make a difference? Depends on your purpose, the instrument, and so forth.

You have to be careful with extremely fast focal lengths (F3) and narrowest of narrowbands. (THe light shifts a bit, and the filter loses efficiency. It does not pass as much of the desired light). Most of us will never have to worry about that difference.

If you are a serious, serious imager, or beset with major light pollution problems, and want to image under bright moons, etc. Go for the more expensive narrowbands from Astrodon, etc.

If you just want to get some good pics, the Orion set, with a wider bandpass, is satisfactory. The ATWB Image of the day from Tuesday (Jan 31) of the Horsie and Friends was taken from a moderately light polluted suburb with the Orion Set. If you get hooked, you have not lost too much on them when you sell them to trade up to Astrodons.

Alex

Just as interesting as the fact that they are headed upward, have you noticed how much more stable they are. A few months back we were having hundred of point swings per day in the DJIA. Now it seems that the traders are basing things more on fundamentals than on flash news reports, etc.

Alex

Other people have made mirrors from glass like that. In doing so, you must be aware that it is ultra thin.

This is good because it is relatively light. So, your telescope as a whole will be much lighter. On the other hand, many people use that extra weight at the bottom to help balance the top.

Because the glass is thinner, it will not have the thermal mass of thicker glass, and will thus cool more quickly.

THe ultra thinness of the blank will require extra care in building a mirror cell that can hold it flat in whatever position. Ultra thin glass can flex more than its thicker counterpart.

Working an ultra thin mirror can present its own difficulties. When pressing on an area of the glass to shape it, the glass itself can flex. In effect, pressure you think you are putting on the blank is in fact being transferred to the supporting surface behind it. This is something you have to take into account. Also, testing with the Foucault tester must be done rather carefully, since the thin glass will flex into a potato chip figure unless supported well in the cell.

It is made of plate glass instead of pyrex or some other material. Plate glass is fairly easy to work (shapes relatively easily with normal grinding and polishing materials). On the other hand, is is not as thermally stable as other materials. This means that it will change its shape more in the course of an evening as the temperature changes. This will affect the image. On the other hand, it may not be as big a deal where the ambient temperature remains fairly steady as the day turns into night, and through the evening (as in the tropics).

And, as the other poster has pointed out----it is tough to start on a sixteen incher. Better to start on a smaller mirror and learn what you are doing before taking on a larger one.

At sixteen inches, you will need a fairly short focal length/F ratio. These are relativley more difficult to get right, and more demanding overall. It is good to have practice on the smaller blanks first. Make a mistake on a sixteen incher, and it takes some work to get it back where it belongs. Make that same mistake on an eight and you can fix it quickly. Best to practice the basics on the little ones.

Alex

A red dot laser collimator can give a false reading if the telescope is not set up properly in the first place or if the laser itself is not properly used.

If, for instance, your laser is not pointed in the middle of the secondary (actually to a point near, but not quite, the middle), you can get a perfetly good return bounce, but improper collimation.

Alex

You can buy such off the web, but curiously they are more expensive than if you make your own. You can make your own if you can find the part that goes into the camera (the false battery casing). That part is available from a cheap AC-Canon converter for your camera (available on some of the auction sites on the web). Simply cut off the part you need, plus the cable that goes to it. Connect that wire to the output of a transformer that puts out about 7.5 or 9 volts. They are available at car stores. THey have a 12 volt cigarette lighter male on one end, and wire coming out the other. Someplace they have a switch that allows them to choose 5, 6, 7.5, 9, and so volts. You may well already have one around the house.

Switch to output to 7.5. The Canons ask for 7.8, but will run on less. Be sure to match the positive and negative ends. The way you do that is to measure which part of the battery casing puts out positive, negative, etc.....and by how much. However you wire your converter, be sure that the readings coming off the battery replacement matches (within a volt or so) the output of the original battery.
Alex


Alex