# I'm considering buying a telescope, which type should I choose?

I am considering buying a telescope for amateur viewing. I am planning to view the stars from my backyard, which is in an area with reasonable light pollution (most of Orion's primary stars are visible). As a result of the light pollution, I have not been able to see more fascinating parts of the sky, such as nebulae. I am looking for a telescope with a limiting magnitude of at least $$+12$$, an angular resolution of $$0.5 \text{ arcsec}$$, is relatively easy to assemble. My budget is between \$500 to \$800.

I've taken note of the Orion Skyquest models, especially the 8" and 10" Build-A-Scope Classic Dobsonian Telescopes. However, before I buy them, I'd like a second opinion from this community. I have seen that it is not compatible with astrophotography devices like an iPhone without extensions. Is there anyone who can give me some recommendations?

• May or may not be closed as opinion based, please let me know where this should belong, if any. Sep 28, 2021 at 2:14

Let's first clean up some misconceptions: Do you live on Cerro Paranal or something like that? If that's not the case, you won't ever be able to achieve resolution of 0.50 arcseconds, like for example, in Edinburgh. That's why I just won't listen to this condition since we are always surrounded by air and you can rarely get the resolution below 1 arcsecond.

The limiting magnitude depends on the observer, the light pollution amount, and the weather conditions. As well, that's why I won't listen to this condition.

There is also a misconception that the telescope is all that matters. But that's wrong. Really good eyepiece is often better than a bigger telescope. Therefore, you need to include around \$100 for additional accessories, or even above \$200 if you want to get serious.

First you might want to consider what do you want to observe. Is this the Moon, the planets, the galaxies, the nebulae, the clusters, the Sun, or the Earth? We can roughly divide these telescopes into 2 categories: planetary telescopes and deep sky telescopes. Note, that when you choose the telescope of one category, you aren't limited just to the planets (and Moon, Sun), or to the DSOs (deep sky objects); the planetary telescopes just have higher magnification and are therefore more suitable for the planets. Let's go look at these two categories, one by one.

## The Deep Sky Telescopes

With these telescopes you can see all sorts of things, not just the deep sky objects (DSOs). I can recommend you Sky-Watcher 10 inch Dobson (or the cheaper 8 inch version; it is not such a big difference). Why wouldn't I recommend the Orion one (of same size)? The finderscope operates using a red dot (it projects a red dot onto the sky) but this isn't so practical. I prefer the monocular finderscope with crosshairs on the Sky-Watcher telescope since you can already see the globular clusters and the nebulae in the finderscope, so it is much easier to find them. This might be the cause of a slight price gap between those two.

You should also invest in some better eyepieces, Barlow lens (2×, 3×, or 5×), the Moon filter which attaches to the eyepiece (yes, the Moon is too bright using such large aperture), the Sun filter which attaches to the aperture (for the sunspots), some filters for the planets or the DSOs, a collimator, but you aren't obliged to do so.

## The Planetary Telescopes

For general observing I would strongly recommend you the DSO telescope, but if you are really interested in observing the planets, the Moon, and the Sun, you should buy some Schmidt-Cassegrain telescope. Such telescope essentially wraps the focal length multiple times so that it can be easily transported, but has very high magnification. The accessories can be the same as with the DSO telescopes.

But, you made some interest for the astrophotography!

## Astrophotography

There doesn't exist any telescope that would naturally enable photographing using a smartphone. Fortunately, there exist special adapters. But you must know that the light reflects on the primary mirror (1), reflects on the secondary mirror (2), refracts in many lenses in the eyepiece (3), refracts in many lenses in the objective of the smartphone (4) and lands on the sensor. The quality of image is then degraded and every dust that comes across the optical path is the problem. Many smartphones don't enable manual mode, as well.

Fortunately, there are solutions. You might have some DSLR lying around. If the objective can be taken off, you are on the horse. You just buy the T-adapter and connect it with the camera sensor. Let's see if we have somehow shortened the path: primary mirror (1), secondary mirror (2), DSLR sensor. There is less dust on the optical path. Also, we solved the issue of the manual mode, most of the DSLR cameras do have manual mode.

If you are more serious and want to invest more, you could buy a dedicated planetary camera. An example is the ASI120MC. You make a 5 min video of the planet or the Moon and stack it in the special software. The results are stunning. (Left is a single image, right is a stacked image.)

Why only a 5 min video?

Since you are pretty active on this site, I believe you know the difference between the equatorial and horizontal coordinate system. The telescopes that are intended for the astrophotography are the equatorial ones (you can change declination and the right ascension). But you said that you want the Dobson (and you are right, the equatorial mounts are just too expensive for your budget). Here comes the problem: the objects don't rotate under the equatorial system, but they do under the horizontal system:

That's why you can't have the photographing session longer than 10 minutes. Also, you would need to manually find the object, wait for it to run across the sensor and repeat the procedure.

You might have fallen asleep while reading this post (I forgive you), so I also added the conclusion:

Why wouldn't I recommend the Orion telescope? Because the red dot finderscope is not too practical to use. The monocular finderscope is better.

I prepared three plans for you: (You can cross something out, or add something new. But note, that you can always upgrade your observing equipment.)

Minimal plan:

Visual plan:

Planetary astrophotography plan:

But note that you can always invest in something more, especially in the Moon filter, and the Sun filter.

You can tell me later how you are satisfied with these choices.

• +1 great answer! I've just submitted my own, and have disagreed with you in a couple of places, I hope you don't mind :-) Good point about the 0.5 arcsec resolution: where I live the best I get is around 0.6, and it's rare. Sep 28, 2021 at 22:42
• Also, regarding astrophotography and rotation: you're absolutely right, of course, but software such as Deep Sky Stacker will detect and correct field rotation when stacking. Luckily, the Moon and planets are so bright that a five minute video is more than enough. Sep 28, 2021 at 22:46
• Have you used Deep Sky Stacker for the planet stacking? Sep 29, 2021 at 17:21
• No, I've only used Registax for stacking planets and the Moon, and DSS for everything else Sep 29, 2021 at 19:43
• Ok, I just thought that Deep Sky Stacker is used for planets as well and I didn't know it : ) Sep 29, 2021 at 19:48

TL;DR: get the telescope with the largest aperture than you can afford, can physically move, and have space to store.
This will be a Dobsonian between eight and twelve inches.

When I bought my first telescope my main considerations were budget and the light pollution where I live.

When you live in a light polluted place then you'll need a wide aperture in order to gather as much light as possible.

When you have a tight budget then you'll want most of your money to go towards the optics.
The mount is important, too: there's no point having great optics but then not being able to point the telescope at the things you want to look at.

This basically narrowed my choices to a Newtonian reflector on a Dobsonian mount.

A reflector is the cheapest way of getting a large aperture. A parabolic mirror is a lot cheaper to make than a refracting lens.
Just look at the prices of even the most basic refractors, and see how quickly they increase as the diameter increases.

A Dobsonian mount is the cheapest and most simple way of making a mount.

User123 has already given a good answer to your question, but I'm going to disagree with some of their points:

1. An eyepiece is often better than a bigger telescope

It's the telescope which gathers light, and this is fixed. A good eyepiece won't make a bad telescope any better, nor will it make a small aperture able to gather more light.
A telescope and eyepiece combine to create an optical system, and it's this system as a whole which should be considered.
What a good eyepiece will do is to ensure that that part of the optical system will perform at its best.
And what is true is that you'll probably end up spending more on eyepieces than on telescopes, long term! :-)

However, you don't need to worry about eyepieces right now. A mass-produced Dobsonian will come with two eyepieces in the box: usually a 2" low power Erfle eyepiece of around 30mm focal length and 70° apparent FoV, and a 1.25" high power Plössl eyepiece of around 9mm focal length and a narrow apparent FoV.
These are just fine to get you started. The best thing to do is to use these bundled eyepieces for a while, until you gain some experience, and then you'll know what you'll want to improve.

(You might still want to buy an eyepiece along with your telescope, though, and if you do then I would suggest you get the Baader Hyperion Zoom Mark IV, in the bundle with the Barlow lens attachment. This single eyepiece will offer you maximum versatility: it'll let you go for high magnification views when your seeing allows, and allow you to zoom out to be able to easily reacquire your target when it drifts out of view. Its only drawback is a relatively low FoV.)

1. Consider what you want to observe

If it's your first telescope then you'll want to observe everything!
To look at everything then a Dobsonian is a good all-rounder: long focal lengths for good high-powered views, and 'fast' focal ratios for wide field views.

I consider Maksutov-Cassegrains, Schmidt-Cassegrains, and long focal length refractors to be specialist telescopes. Great for looking at solar system objects, globular clusters, and planetary nebulae; but the FoV is too narrow to observe extended objects like large nebulae and open clusters, and it can be hard to find targets - especially without a good (expensive) Go-to mount.
Short focal length refractors give great low power wide views, but don't go very high.
One of these will be the second or third telescope that you buy, once you've gained some experience and you know that you specifically want one.

"Second or third telescope"? Yes...if you stick with the hobby then one day you'll buy another telescope. Most amateur astronomers have at least two telescopes, and will probably be planning on buying even more in the future.
(Personally, I spent a few years with a ten inch (250mm) Dobsonian, but it's not easy to travel with, so I bought an 80mm refractor to be able to take on a plane; and I'm considering getting a 130mm Maksutov for those high-power views of planets.)

I agree with pretty much everything else User123 says, though :-)
Get a Dobsonian with a magnifying finder scope, rather than the one with the red dot.
A red dot finder is fairly worthless on a Dobsonian - especially under light polluted skies - it doesn't magnify the view so doesn't show you any more. If you want a non-magnifying finder later then get a Telrad: it has markings which help measure distances and position the telescope to find things.

Also consider the mount. Not all Dobsonian mounts are equal. You're going to be moving it left and right and up and down a lot. Compare reviews and see what they say about the mounts.
Generally, the bigger the trunnions the better - a larger surface area there will give a smoother up-and-down (altitude) movement.
When I bought my GSO 10" Dob, there were two options: the standard and the "deluxe". I went for the deluxe version because the mount was improved: the standard version had a simple Teflon pad in the base for the left-and-right (azimuth) movement and smaller trunnions, whereas the deluxe had a "lazy Susan" plate with bearings and larger trunnions.

Finally, forget about astrophotography for now. Sure, buy a cheap attachment which will let you position your phone above the eyepiece and take some photos of the Moon and Jupiter, but you'll need to buy more equipment to be able to take photos of the fainter objects out there.
This isn't to say that astrophotography with a Dobsonian is impossible - not at all: I've dabbled in it myself - but you'll need a very sensitive camera and use a different technique, and the really faint objects will still be out of reach.

If you want to start doing astrophotography then it requires completely different equipment to visual astronomy: it's all about the mount. Spend a lot of money on a mount, put a small (50-70mm) short (f/5 or less) refractor on it, and use a colour astrocamera with it.
Then get used to spending more time processing the resulting data than you did capturing it.
After that, move up to a monochrome astrocamera, lots of filters, and bigger telescope, and a bigger mount.
It's a rabbit hole and a money sink.

Halfway between visual astronomy and astrophotography is electronically assisted astrophotography (EAA).
This is where you use an astrocamera with a very sensitive sensor with a program which does "live stacking" (on Windows this program is usually SharpCap, and on Linux it's ASTAP).
This gives almost instant results, and under light polluted skies can be the only way to see some objects.
I personally have seen some galaxies using this technique which are otherwise invisible to me.

Conclusion:

Buy an eight, ten, or twelve inch Dobsonian. All of these will be about the same length - they're usually: 8" F/6, 10" F/5, 12" F/4.
A final consideration is that the 'faster' (shorter focal ratio) the telescope, the more expensive the well-corrected eyepieces. Reflectors suffer from "coma" - a stretching at the edges of the view which is more pronounced at shorter focal ratios.
You can buy a coma corrector to correct this, but again, that's even more money. (Sometimes it feels like it never ends! The initial \$800 budget easily turns into thousands spent over a few years!)

Check the classified adverts in your area if you don't mind buying second-hand. You'll save a lot of money doing this. On the other hand, until you have some experience it'll be hard to know what issues to look out for with second-hand equipment.

If your budget is a hard budget then go for a slightly cheaper telescope so you have some left over for accessories - the book Turn Left at Orion, for instance, is a good companion to a first telescope.
If your budget is a soft budget then blow it all on the telescope and then in a few months you'll get to know what additional bits and pieces you'll want.

Finally: good luck and have fun!