Tumbleweed Observatory's

Astronomy Hints



Tips And Hints On Astronomical Telescope Types And Use

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Smart Telescope Tips For Amateur Astronomers

Learn from these smart tips and hints from other amateur astronomers. These tips are not guaranteed to work for you, but hopefully you'll learn a thing or two.

Hints Index

Consider A Long Focus 60mm
How To Improve Newtonian Performance
Used Refractor Checkout
Improving Focus With Bigger Knobs
Best Way To Use NexStar AC Adapter

Posted: 8/28/2011

Title: Consider A Long Focus 60mm

I admit to having been a bit of a telescope snob. I bought into the idea that you needed at least a 3 inch refractor or 6 inch reflector to do "serious" work. So I primarily worked with 6 inch and 8 inch reflectors for may years. Then I joined a 60mm telescope egroup on yahoo.com, and found there there were a number of very enthusiastic small refractor users out there. And not novices, but long timer serious observers. Since I'd never really used a quality 60mm, I set out to try one.

I bought parts to build a long, 1000mm focal length 60mm. That's about an f/17 telescope, even longer than the classic f/15 system. I built the telescope to use 1.25" eyepieces, and mounted it on a very solid pipe-fitting tripod. I can only say that I'm amazed at how well it performs. I've viewed transits of Jupiter's moons, countless moon craters, some detail on Mars, and enjoyed very nice views of Saturn. Double stars are a snap.

I've also looked at some DSO's, though I'm not nearly as adapt at that as more experience small refractor users. But I've been able to easily find many open clusters, M57 the ring nebula, a few globular clusters, and of course M31, the Andromeda galaxy. The journey has just begun.

So given that good 60mm telescopes are available at very reasonable cost (especially used ones), give one some thought, and quit spending an hour waiting for your reflector to cool down every time you go out.

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Posted: 8/28/2011

Title: How To Improve Newtonian Performance

A few years ago I purchased an f/5 Newtonian on an equatorial mount from Discovery telescopes. I've found it to be a very solid telescope with excellent optics. But the overall telescope design had room for improvement.

The telescope optics were mounted in a thin-walled metal tube. A heavy plastic support ring that also provided the 3-vane spider for the secondary helped stabilize the front end of the telescope. The primary mirror mount also served as a stabilizing support for the rear end of the telescope.

But the 3 spider vanes, being plastic, were nearly 1/4 inch thick. They caused terrible diffraction spikes around bright objects -- especially Mars. So I removed the spider support, leaving only the support ring. Then I created a thin metal curved secondary holder. This secondary support is less than 1/16 inch thick, and being curved causes NO diffraction spikes. The views are much more pleasing.

I also noticed that though the interior walls of the telescope tube were painted flat black, there could still be some specular reflections caused by the smooth metal surface. So I put black flock paper on the inside of the tube. Since the telescope is only 30 inches long, this wasn't a difficult task. Now I get really nice views through the telescope, for an out of pocket expense of just a few dollars.

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Posted: 8/28/2011

Title: Used Refractor Checkout

Here's something I learned from a yahoo egroup dedicated to 60mm telescopes. I obtained a used "vintage" 60mm refractor. It's a Monolux brand, one of many pretty good Japanese makes of yesteryear. The telescope is a pretty common design, that being a 700mm focal length achromat (2 element objective).

Daytime views seemed reasonable, but my first night out I found the view of Saturn to be pretty bad. Observing a star I found that the inside/outside of focus diffraction patterns looked totally different from one another, and the image of Saturn just wouldn't come to a sharp focus.

A club member mentioned that many of those older refractors have been disassembled at one time or another for a lens cleaning, and often the objective elements don't get put back together in the proper order. I ended up trying the two objective lens in all combinations to see if any combination gave good images. One certainly did. The telescope then produced a pretty good image of Saturn, but showed just a bit of astigmatism.

At another suggestion I spent an afternoon critically examining the image multiple times after rotating the lenses with respect to one another. I rotated them about 20 degrees per try. I eventually found a point where the astigmatism was virtually eliminated. I used a felt-tip pin to draw a mark across the edges of the two lenses so I'd know how to position them should I ever remove them for cleaning.

So the point is, if you have or get a used 60mm or similar sized refractor and find it gives poor images, mark the lens edges so you can put them back in the order they were, then try the lenses in different arrangements. You may find as I did that the lenses had simply been removed and erroneously re-assembled in the wrong order.

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Posted: 8/30/2011

Title: Improving Focus With Bigger Knobs

This is perhaps an old suggestion, but it's a good one. Many focusers on telescopes have rather small knobs, 1/2 inch in diameter or even less. You can help improve your ability to achieve sharp focus simply by replacing the knobs with bigger ones, like 1 inch to 1 1/2 inches.

For example, I love my ETX 90 RA, but one thing that can be tedious when trying to see that finest fleeting detail is being sure the telescope is sharply focused. The focus knob on the ETX is about 3/8 of an inch in diameter. Larger replacement knobs have been around for the ETX, but I found a cheaper solution. I dug through my wife's craft parts drawers and found some small clips designed like miniature clothespins. They're about 1 1/2 inches in length, and can just open wide enough to clamp onto the ETX focus knob. This makes a focus lever that sticks out about 1 inch from the center of the knob, giving an effective diameter of 2 inches. A regular clothespin would stick out far enough to be in the way, but the mini-clothespin is perfect.

So I get to rough focus, then clip on the mini-clothespin for fine focus. It helps quite a bit. Give it a try. I always us the technique when taking photographs through the ETX.

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Posted: 5/05/2013

Title: Best Way To Use NexStar AC Adapter

I found out the hard when using my newly aquired (used) NexStar 5 SE powered with the AC adapter that it doesn't work that well if there are no batteries in the NexStar base. I found that when powered only by the AC adapter, at least a couple times per viewing session that the mount would freeze -- just stop moving. Sometimes there was an error indicated on the hand controller's display, usually something about loosing contact with the motors. At other times, the display would just turn off.

As you might expect, whenever the unit froze up, the current alignment was no longer valid, as the computer no longer knew the mounts orientation. So I'd have to go back through an alignment procedure.

An egroup acquaintance suggested that the NexStar mount might work better if I put batteries in it, even though I was powering it through the AC adapter. I tried that, and I haven't had a freeze up since. I suspect that either the power plug contacts can get a bit intermittent while the base is turning, or perhaps the AC power is occasionally insufficient if the motors draw too much current. Whatever the cause, simply leaving batteries in the base seems to solve the problem.

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