Useful Article from EzineArticles: Resolving Power of Telescopes

• Author: admin
• Filed under: Buyer's Tips, telescopes
• Date: Jun 16,2008

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How to choose a telescope: Magnification revisited…

• Author: admin
• Filed under: Buyer's Tips, telescopes
• Date: May 22,2008

We’ve realized that in all of our ‘how-to-choose’ articles, we make a concerted effort to warn prospective buyers of optical instruments against magnification hype. And for good reason too. We still see people around us falling for that trick and ending up with instruments that have either poor optics or insufficient aperture or both. Hopefully our readers do not fall prey to the marketing machine anymore. Just to be sure that our newer readers are aware of this trap, we will quickly revisit it here (and expand on it a bit):

While the hyped-up power ratings often seen are not necessarily fraudulent claims (the instrument will usually go to the stated magnification), there is a limit to usable magnification. The quality of the lens, mirrors, eyepieces, etc play a huge role in how much of that power one can actually use. At high magnification, the image and also imperfections in glass are also magnified.

The same goes for movement. At high magnification, movement is also magnified and the slightest movement renders the image completely unusable, and in the end all you can see is a blur! So this is where the usable magnification is clearly determined in part by the quality of the optics and also the quality of mounts and/or tripods.

Lens diameter is a key factor in the amount of usable power and the general rule of thumb, called the sixty rule, states that the upper limit of a telescope’s power is determined by its lens diameter (in inches) multiplied by 60. For example, a 4″ telescope has a maximum usable power rating of 240X. In our experience, if you take 15% off that, you have a more reliable maximum power rating that does not depend on perfect viewing conditions. that And this upper limit pretty much is assuming you have an extraordinarily calm and clear night sky.

So, if you’re after power, then choose a scope with largest diameter lens that you can afford. Large diameter lenses capture more light too, so you are able to view much dimmer objects (Note: a 4-inch scope has four times the light gathering power of a 2-inch scope, and not double).

Optical quality and mount stability are not even a consideration - never compromise on those - its all about usable power, remember? If the image is blurry, its blurry. And that’s that - your first date with your new scope (and maybe even a new hobby) is ruined before the romance could even really get started…

Note

Often a larger diameter scope in the same series is only slightly more expensive than the one below it. These Celestron scopes are a good example. If budget allows, we always recommend higher apertures…

Price: $599.00

Celestron NexStar 4 SE Telescope

Price: $799.00

Celestron NexStar 5 SE Telescope

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Choosing a Telescope

• Author: admin
• Filed under: Buyer's Tips, telescopes
• Date: Apr 8,2008

We’ve written this guide for a beginner, or someone who has been disappointed by his/her first purchase(s). Those with more experience will already have learned a lot in the field or from more experienced enthusiasts, and can make more informed choices.

Do you really need a telescope?

Many many times, people buy telescopes because they think its what they need. In many cases, a good binocular is a better tool for the job, and it is much more versatile and portable too!

Do your research. Ask people who already do what you are planning to do. Save yourself some money and frustration. If budget is a limitation, then a good $100-150 binoculars is more often than not much better than a junky telescope - most times that same binoculars is a better bet even when you have a huge budget. Beginners and even intermediate amateurs do not need fancy telescopes!

Since you should get a high quality telescope that you won’t outgrow quickly or lose interest in, it will be hard to keep prices very low - but there are some good choices that are reasonably priced. Just remember - quality first! A bad choice for your telescope will lead to frustration and disappointment rather than enjoyable nights under the stars. Remember, good telescope can last a lifetime - even longer.

If you’re still convinced that you need a telescope, read on…

Types of Telescopes

There are three main classes of telescopes available to the amateur astronomer:

1. Refractor telescopes - classic “department store look” telescopes that use refracting lenses housed in a long, thin tube mounted on a tripod. OK for viewing the sun, moon and planets where magnification detail is more important than brightness.
2. Reflector telescopes - large instruments that use mirrors housed in large tubes. They really ‘grab’ lots of light and are great for viewing faint, deep-sky objects like galaxies, star clusters and nebula.
3. Compound telescopes - also called cadioptric telescopes, They use both refracting lenses and reflecting mirrors, which provides compactness. Designs include those of Schmidt, Cassegrain (Cass), Maksutov (Mak) and hybrids.

Buy from a reputable dealership

While this seems like just pure common sense, many a potential enthusiast has had their envisaged love-affair with optical systems destroyed very quickly because they paid good money for bad equipment from a ‘gadget supply store’. A telescope is not a gadget. It is a marvel of physics and should be seen as such. So buy from a reputable store, whether online or traditional ‘brick and mortar’.

Beware the power/magnification hype!

We say exactly the same thing in our guide to buying binoculars. Shrewd manufacturers and dealers use the promise of magnification to hypnotize and trap the unwary newcomer. The outrageous (for what is being sold) specifications of 400x, 1200x, etc magnification is just hype and has no relation to actual usable power.

Aperture rules, OK?

Just as with binoculars, what you should be after is aperture, which is determined by the objective lens. The more light it can capture, the clearer and brighter the image.

While many lower-end ‘budget’ telescopes perform OK on a bright day, they are almost useless at night. And trust us, even if it was not the originally intended use, most telescope owners eventually turn their instrument to the heavens on a cloudless night, hoping to see what they see in magazines and on the Internet. A large percentage of them end up very disappointed. So, forgo power for aperture (after you have identified a reputable dealer of course).

Both light gathering and resolving power increase as apertures increase, which means that you will be able to see dimmer objects. Note: a 4-inch scope has four times the light gathering power of a 2-inch scope, and not double. (2 x 2 =4).

As can be expected, manufacturers are starting to push larger lenses as ‘beginners’ do more research before they buy. The end result is the production of telescopes with reasonable power ratings, large apertures, and junk optical quality. And there is no substitute for optical quality. If everything is just a blur, then you may as well not even look at it. Trust us, its that disappointing!

Buy the smallest telescope for your needs

Of course the previously mentioned factors are most important, but the more portable and easily usable your scope is, the more likely it is that you will have it with you when a great viewing opportunity presents itself. The smaller sized scope coupled with a good mounting also means that you will be able to set up and focus much more quickly than with a huge scope.

Mount stability

Poor stability will turn working with even a very good telescope into a real nightmare. Be sure to budget with a nice solid tripod in mind, and remember that it can easily set you back more than $250 - but it is well worth it - we would even go so far as to say its essential.

Join a club or an online community!

There is not much to be said about this other than that you should learn from other’s experiences and/or mistakes. Ask questions, learn as much as you can. It’ll save you money, time and potential frustration. The advantage of joining an actual club is that you will be able to work with other members’ equipment, even if just for a quick look and feel. Its a great way to identify a short-list of scopes to make a selection from.

All of the telescopes that we strongly recommend below have also received excellent reviews from others like you, the buyer/enthusiast. You will do well with any of these, but the more sophisticated ones will be with you for a very long time, since its hard for even an experienced amateur to ‘outgrow’ those.

Recommended telescopes (in order of cost & ’sophistication’)

Meade ETX-80AT-TC Astro Telescope with AutoStar

Automatic finding and tracking of thousands of objects

AutoStar Suite Astronomer Edition Software

Instructional video

Compact and easy to use

Zhumell 8-Inch Dobsonian Reflector Telescope

Celestron NexStar 130 SLT Telescope

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