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Articles

How to select your first telescope.

by Bigzmey

Google the topic and you find tons of hits. Refractor vs reflector, DOB vs SCT - plenty of strong opinions on all sides don’t make selecting the first telescope easier for newcomers. In part, this is because we as observers develop our own preferences over the time and are passionate about the hobby; but also because there is no do it all telescope. Since selecting one is always a compromise, what's good for the goose is not always good for the gander.

Instead of telling you what telescope to buy, I would like to guide you through the selection process and help you to decide what scope would be the best option for you.

Don’t buy your first scope as your lifetime scope

Consider your first scope as training wheels instead. It does not need to be perfect, just decent enough. The goal is to get into observing first, gain some experience and learn what you need in the second scope. Almost any entry level telescope with exception of a few Bird-Jones design scopes should work fine as a training scope, making the choice easier and less stressful.

More on Bird-Jones design is here.

https://theskysearchers.com/viewtopic.php?f=4&t=5803

Factors to consider: Budget > Size > Mount > Scope design

Like with cars, computers, cameras, etc. more money would typically buy you better quality and more enjoyable scope. Still, whether you are spending $100 or $1000 you will not get all points checked on your wish list. You need to decide which features are more important for you and which you could compromise, and select the right combination within your budget range.

When considering the budget, allocate at least 30-50% of it for the accessories. Most scopes come with accessories which are barely adequate at best. Be prepared to spend money on better finder, diagonal or a couple of eyepieces. You will need a red light to preserve your night vision. Also, strongly consider observing chair or other means of sitting while observing.

Aperture vs size and weight

For visual observing telescope aperture is the most important feature. If you are lucky to have access to dark skies even a small 3-4” scope will show you hundreds of targets. Most of us however live and observe under light polluted skies. At the place I live I have run quite fast out of DSOs I can observe with 80-100mm telescope. I could still enjoy targets which are not affected by light pollution like Moon, planets, double and carbon stars. But for DSOs I had to step up to 8” telescope. Why not 12” or 14”? Beside the fact they are more expensive, scopes grow considerably in size and weight and at a certain point become too heavy to handle and enjoy.

I feel that 4”to 8” is a good range for starter scopes. Not too heavy or large, or difficult to handle, but enough aperture for casual observing. If you become serious about astronomy you can get a larger light bucket later as you advance in hobby.

Mount

The second most important feature after aperture is the telescope mount. No matter how sharp is your scope, shaky mount or mount which is hard to operate would make your setup useless. Wobbly mount is the weakest point of entry level telescope packages. It is almost always a better strategy to select a good quality mount and then look for the scope within your budget which would ride well on it.

Manual or GoTo Mount

First thing selecting right mount is to decide whether you want manual or GoTo mount.

With manual mounts you will find your targets in the sky using bright stars and asterisms as navigation points and sky charts, phone apps etc. to guide you there. It is like driving a car using road atlas and following road signs.

With GoTo mount you align the scope using a couple of bright stars. After that the mount can find targets for you. This is like a self-driving car.

Finally, there is a Push To option - after proper alignment, handset or other type of device will tell you where to push your scope to find the target. This is like driving with GPS.

With a manual mount you will learn the sky and constellations faster and experience the thrill of hunting for your targets. However, under light polluted skies with only a few brightest stars visible this process may become too slow and painful to enjoy.

GoTo or PushTo will help you to find targets no matter how dark or light is the sky but add another layer of things to take care off (batteries, cables, alignment, etc.). Even with computerized mounts it pays to learn the skies, since there are maybe issues with GoTo accuracy which you will need to resolve. GoTo mounts are typically more expensive than manual. Thus, prepare to spend more or settle for a smaller scope if you go GoTo route.

Due to the Earth’s rotation the objects move in the sky from east to west. In order to keep them in scope’s view you can either manually track them by moving the scope or employ motors. GoTo mounts track targets by default. Some of the manual and PushTo mounts can be fitted with tracking motors.

Equatorial or Altazimuth Mount

There are two main types of mount design: Equatorial and Altazimuth. You can read in more detail here

https://en.wikipedia.org/wiki/Equatorial_mount#Astronomical_telescope_mounts

https://en.wikipedia.org/wiki/Altazimuth_mount

Both types of mounts could be manual, GoTo or PushTo. AltAz mounts are typically faster to set-up, easier to learn and are more compact and lightweight. EQ mounts provide more accurate tracking, ease to reacquire lost targets, but are somewhat more complex to learn and operate.

Unless you already have a preference for one type or another, the type of the mount should not be the deciding factor for your first scope. Rather you should look for most stable setup within your budget.

Some of EQ mounts can be used in AltAz mode, and some of AltAz mode can be set on a wedge to emulate EQ. There are also hybrid mounts designed to operate in both modes.

Optical design

To start, I would like to encourage you to read about different telescopes (reflector, refractor, catadioptric) designs. Neutral resources like Wikipedia or Astronomy textbook would serve the best. Many misconceptions, outdated info and exaggerations have been propagated on forums about telescope designs. Reality is that all three main designs can deliver great quality views, none is superior or inferior to the others, and all have weak and strong sides.

https://en.wikipedia.org/wiki/Optical_telescope

Therefore, unless you already have a preference for particular scope design, don’t select your scope based on the design. Rather select design which fits the best your lifestyle and budget (see below).

My only advice here - don’t get a first scope which is too specialized. This has to do more with telescope Focal Ratio then with scope type.

F-ratio = telescope focal length/ telescope aperture.

Scopes with focal ratio below F6 are considered fast scopes. They are typically more compact and lightweight, which makes them good candidates for travel sets or grab and go setup. They also more stable on the mounts due to shorter length. However, due to the optical aberrations associated with fast scope designs, the image quality degrades faster at higher powers compared to the slower scopes.

Scopes with focal ratios F11 and above are considered slow scopes. Slow refractors and reflectors have long tubes, weigh more than faster scopes and will need heavier mounts for stability. They deliver better optical quality compared to a fast scope but provide a narrow field of view. Slow catadioptric scopes are lightweight and compact due to the folded design, but they still have a narrow field of view.

Finally, there are scopes with mid-range focal ratio F7 to F10. They are in the goldilocks zone as far as image quality and field of view go.

For newcomers the Moon and planets reign supreme and for a good reason. They are easy to find and provide the most striking views. Starting astronomers also like to see a few famous DSOs, Orion Nebula, Pleiades, Andromeda Galaxy, etc. Many of them are quite large.

Typical eyepieces provided with scopes or purchased as starter kits are Plossls/Kellners with narrow 40-50 degree field of view and short eye relief in low focal lengths.

So, what typically happens with fast scopes? Beginners manage to find targets thanks to the wide field low power views, but with low quality stock EPs and barlows planets come out as blobs of light. The owners start looking for quality EPs in short focal length and discover that they may cost as much as their scopes.

Slow scopes are on the opposite end. Moon and planets look nice even with stock EPs, but beginners are frustrated with finding DSOs due to the narrow field of view of slow scopes. Even if they manage to find the target, quite few DSOs would not fit to the narrow field of view.

Therefore, I feel that mid focal ratio F7 to F10 telescopes make better beginner scopes. They will perform well on planets, Moon and brighter DSOs, even with stock EPs.

Select telescope to fit your lifestyle

The best scope is the one which gets used. Consider how often you would like to observe, how much time you would have for each session, the place where you will store the scope, and where you will be observing.

Large scopes take longer to setup and take down. They need time to acclimate if you move them from inside to outside. Thus, they are better suited for longer observing sessions. However, if you live under light polluted skies but still like to observe DSOs, you should get as large scope as you can buy and handle.

What if you do not want the hassle of a large and heavy scope? You can still observe with a small scope from within the city but pick targets not affected by light pollution, like the Moon, planets, double stars and a few dozens of the brighter DSOs.

If you can only commit to short observing sessions, or you need to carry your scope to the observing location, getting a small compact scope on a lightweight mount would be the way to go.

Also, consider alternative uses of your telescope. If you like to watch birds, ships etc., refractor or catadioptric telescopes can be fitted with correct image diagonal for daytime terrestrial observing, or even used as photo lenses.

Accessories

In order to keep the prices attractive, the accessories included with starter scopes range from mediocre to plain junk. Still, you should be able to find and observe the Moon at least. Don’t jump into buying accessories before a session or two with your scope; and don’t buy EP/filter kits as they are a waste of money. Instead look for accessories, one at a time.

Most likely you will need to upgrade the diagonal, add or upgrade the finder, buy a filter or two, and a couple of EPs.

Buying and selling your first telescope

Try before buy is always good. Many astronomy clubs have telescope loaner programs.

Buying from Amazon or similar with 30 days free returns is a good idea.

Check your local Goodwill stores and classifieds or online resources (eBay, CloudyNights, Astromart). Often you can find entry level scopes in a good shape for pennies on a dollar.

Now, you had your first scope for a while and thinking of upgrading it, or it did not work for you, or you tried and decided that astronomy is not for you. Good news is that astronomy equipment basic or advanced is not that hard to resell. Many local and online photo and astronomy stores buy used equipment, and you can always sell on eBay or classifieds.

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