Choosing Your First Telescope for Astronomy: Complete Essentials

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One of the most watched telescopes on eBay is a TINY 76mm Newtonian reflector!

DO NOT WASTE YOUR MONEY ON TINY OPTICAL RUBBISH - Tiny little telescopes will not show you anything useful... They will disappoint every time!

Do yourself a favour and invest twenty or so minutes of your time reading this guide to avoid regretting your first telescope purchase for life! 

You can get an instrument capable of giving years of good astronomical views for around a week's wages... Read on!

There are plenty of eBay and YouTube guides about buying telescopes and they will ALL point you away from Newtonian reflectors under 120mm diameter - And quite rightly! Please read on!


Updated - February 2016
First published by me 2010.


There is a very good reason that so many disgruntled people are selling their tiny telescopes on eBay...

                                          ...It's because tiny telescopes are no good for astronomy!



Sooner or later, if you're interested in astronomy, you'll decide you want a telescope... If you buy yourself the wrong one, you will probably end up giving up astronomy because your expectations have been let down. My advice will save you throwing away money and will get you a telescope that you will be able to keep using for many years without great expense.

 Allow me to guide you towards your first 'scope with an explanation of the considerations you need to make while choosing.  

With qualifications in astronomy, having been a director of an astronomical company, and with over forty years experience in observational astronomy, I hope you will trust my informed guidance in this matter.
In this guide: Lots of Photographs, Illustrations and a couple of Videos


The two types of telescope I am going to recommend are: 'Astronomical Refractor' and 'Newtonian Reflector'. (I will generally refer to them as Refractor and Newtonian to save confusion between refractor & reflector.)

The reason I recommend only these two types is that these are the two best suited to the beginner because they are the simplest and therefore have the largest aperture for your money available - So you can get into the right SIZE of telescope with the minimum outlay.



The refractor is the telescope with the big lens at the front and you look in the small end!

If you're buying one of these make sure it's an 'astronomical refractor'

Try to avoid anything shorter than f8 REFRACTOR (f numbers, see later)
You'll need one with a front lens (Object Glass) of AT LEAST 80mm to see anything useful! (90mm ... all the better for not much more money!)

A mounting with slow motions is almost essential.

Refractors are particularly good if you're interested in the planets, double-stars or the moon (Though they can be used for any subject with experience). They show great detail for their size and when used on the relatively bright planets, the objects are easy to locate, even given the small field of view.

The newcomer to telescope use will find the small field of view and high focal ratio of a refractor make it difficult to find 'Deep Sky Objects'. A beginner who wants to look at Galaxies and Gas Clouds would be best to get a Newtonian Reflector (See below).

Refractors are robust and can stand a good deal of handling without going out of alignment. The refractor is the telescope type that transmits the most light for its size and reveals the best detail. All other types have some sort of obstruction in the light path and this deteriorates from the image. All Refractors suffer slightly from false colour but on most objects this is minimal.

Nice: Paul Money's 127mm (5") f9.45 Astronomical Refractor - A very nice bit of kit. (Courtesy Astrospace)



Great Start: 90mm (3.5") f10 Astronomical Refractor - A very good first telescope. New only £139 (Jan 2016)



This is the simplest type of reflector. They use a mirror to focus the light instead of a lens and the observer looks into the side of the tube instead of up it!
You'll need one with a parabolic mirror AT LEAST 130mm in diameter and 150mm is all the better!  I will assume you want more than the bare minimum and will continue this guide refering to the 6" 150mm Reflector as your sensible choice.

150mm Newtonians are good all-rounders.  The short focal length ones (f4 = 600mm to f6 900mm) are especially good for 'deep sky' (Galaxies, Nebulae, Star Clusters). Focal ratios of f6 to f8 are good for planetary views too!
Newtonian reflectors are not recommended for study of the Sun.

A mounting with slow motions is almost essential.
Mirrors can go out of alignment with rough handling - Nevertheless, in my experience it takes quite a big jolt to upset the optical settings - Bearing this in mind it's advised that you be careful when setting up or carrying!
All Newtonian (And ALL other reflec
tors) have obstructions in their light-paths and so suffer from deterioration of the image. However, they are great value for money and give some excellent views on the best nights.


Starter Newt: My 150mm (6") f5 Newtonian Reflector - If these 6"ers are too expensive and you really can't manage - A 130mm parabolic Newtonian will have to suffice!

New £265 (Jan 2016)

Why Does Aperture Matter So Much?

Resolution in the image and 'light gathering power' is dependent on the diameter of the mirror or lens. If you can't resolve the detail then NO AMOUNT of magnification will show it!

You NEED the BIGGEST objective you can manage (either financially or physically - telescopes get heavy!) to allow detail to be shown no matter the magnification used!

The bigger the diameter of your objective (lens or mirror) the more detail will be available for observation.

Here's an analogy:

If you 'zoom' in to a high resolution picture on your computer you can find more detail than if you view the picture in a small frame on screen. But if you print the small frame and use a photocopier to enlarge it there is no more detail to be had.

This is analogous to a larger telescope where higher magnifications can be used as they bring out details that cannot be seen at lower magnifications. (The eye can only see detail that has been presented to it above a certain size hence the need to magnify at all!) The tiny telescope presents all its information at a lower size - Further magnification is wasted, it just enlarges the low-resolution image without bringing out any new detail.

If you use more magnification than the telescope can show detail then this is 'empty magnification'. See magnification section later for more on this.


Left: Approx view of Saturn with 50mm (2.0") refractor or a 80mm (3") Newtonian.
Right: Approx view of Saturn with 80mm (3.1") refractor or a 150mm (6") Newtonian. (I'm happy with this image representing a really still night!)


As far as star images go:

 There are two main considerations: Splitting binaries (Close pairs of stars cannot be split with tiny telescopes or higher magnifications) and the visible star magnitude limit. A larger telescope will always show closer pairs as individual stars and show fainter stars than a smaller telescope will.


Difference!: Left is a 20x view of the Pleiades (M45) with a 6" 150mm telescope (Lower frame). On the upper frame is the same cluster with a 50mm. Note not only the many more stars in the larger telescope, but the splitting of the double star just below centre.
Not just two stars but four are visible in the larger telescope.

Resolution:  The triple star shown resolves itself through use of larger telescopes - Not bigger magnifications.


Have a Look!: This video demonstrates the effect of widening the aperture from 50mm to 150mm and back.

Orion Nebula: The nebula M42 in Orion. Once again the central star is not split with a tiny telescope but shows itself to be a 'Trapezium' of four stars in the bigger 'scope. Also note the amount of nebulosity that can be glimpsed in the bigger telescope (R).


The reason is that the bigger the telescope the smaller the image it can produce. So, small telescopes produce big 'points' of light (Low Res. Images) but big telescopes produce smaller 'points' of light (High Res. Images).

So it follows that if the two stars are closer than the minimum 'point' that your telescope can produce, you will only see an elongated blob where the two circles overlap, instead of two distinct points.  As you use larger and larger telescopes the 'point' becomes smaller until you can see the two distinct stars clearly.

See diagram.  The stars shown are just a connected blob, at any magnification, for any telescope under 140mm / 70mm.

You get to choose which view you would prefer by picking a telescope of the size I advocate in this guide!

Authentic View: Mars at a favourable opposition (Close to Earth). You'll need to look closely - But observe the differences in detail between the three telescopes. Once again you can choose which view you would like by buying the size that gives the view you want!

A reflector transmits only about 85% of the light that enters the system, a refractor something like 98%.


Observe the detail and the brightness differences in the pictures above - These views are representative of the real difference between the different telescope sizes as they appear to the eye when observing on a still night.



Diffraction Limited Optics - A good or bad thing?

You may wonder why your telescope has 'Diffraction Limited Optics'.
It sounds as though that's a bad thing, doesn't it?
Why should you accept 'limits'?

Well, the truth is that all optical systems have a theoretical limit to the detail thay can show.  A small telescope can only possibly show so much detail - A larger one will show more detail (Regardless of the magnification used).
In the diagram we can see that fine detail is not shown in the smaller telescope sizes because they cannot focus the light into a small enough point.  You need larger telescopes to see finer detail.

So, the limit for seeing fine detail in an image is dependent on the accuracy of the telescope mirror or lens.  A lens that is perfect, optically, is said to be 'Diffraction Limited'.  Because the only thing that is limiting it is optical physics.  That is, it's as good as it can be, given the size.

So diffraction limited optics are the best.

Always look for diffraction limited optics when buying your telescope. 
If it doesn't say in the blurb or specification page - ASK!
In a Newtonian Reflector, for example, as we have seen above, the mirror MUST be parabolic to achieve diffraction limited images.  A spherical figured mirror is always out of focus at some point!

The Dawes Limit.

This is the formula for finding the resolution limit of your telescope (If it has diffraction limited optics).

This is also known as The Rayleigh Limit.

R = 4.56/D     D in inches, R in arcseconds
R = 11.6/D     D in centimeters, R in arcseconds
where   :
D is the diameter of the main lens (aperture)
R is the resolving power of the instrument
You can use this information to work out if you can see the moons of Jupiter as discs or not, for example - A very useful formula.

Modern manufacturing techniques mean that it is easier than ever for manufacturers to produce very good optics.  A company like SkyWatcher, for example, produce excellent value, diffraction limited telescopes.  They include this information on all their specifications.  If you're looking at a telescope and it doesn't say' Diffraction Limited', you can bet that they aren't and you'll have inferior views.

The biggest obsticle to your viewing clarity is the atmosphere.  Whilst your telescope may be diffraction limited, it will also, always, be atmospheric seeing limited too.  There are bad nights, good nights and very good nights.  It's all part of the game!


 The brightness of the image in a telescope and the field of view (The size of the circle when you look into the eyepiece) is determined by the diameter of the telescope objective (The main lens or mirror) divided by the focal length and by magnification (Higher magnifications narrow the apparent field of view). If the f number is low (4 - 6) the field will be wide and if high   (8 - 15) the field of view will be narrower.

Here's another analogy!
Think of looking through a toilet roll tube. They're fairly short in comparison to their width (about f6). Now look through a kitchen foil tube (about f10). The field of view is much smaller in the long tube. This is exactly how a long focal length gives a restricted view and can be used to demonstrate well the f number effect on field of view.

Eg: 900mm focal length divided by 90mm objective lens gives f10 (900/90=10) (Which is fine for a refractor but a bit unwieldy for a Newtonian.)

It is usual for
Newtonians to be shorter focal length than the equivalent refractor - So f4 - f8 is usual in Newtonians, whereas, f8 - f15 is more usual in refractors. A refractor with a shorter focal ratio (f number) than f8 starts to show some focussing problems and the false colour around bright objects becomes much more pronounced (Red and Blue fringes) so try to avoid refractors shorter than f8. (A focal ratio of around f10 is a very common size for good astronomical refractors but as a guide f8 should be the minimum you look for. Newtonians of f4 – f8 are common and give good images.)

Visually, the stars are not affected by f number but extended objects, like galaxies and nebulae, seem brighter in low f number systems. If you're interested in 'deep sky objects' then a reflector with a focal ratio of between f4 and f6 would be your best choice.



(This does not apply to refractors)

Small Newtonian reflectors often have spherical figured mirrors. The mirror's shape is incredibly accurate and MUST be parabolic to bring all the rays of light to the same focus.

If you want to get the best out of your telescope, and use the optimum magnification and have the best images you need to have a telescope with a parabolic mirror. That usually means at least a 150mm Newtonian.



Ray Diagram: The parabolic mirror gives much sharper point images (The detail on the planets will also be smudged by a Spherical mirror). The spherical mirror produces out of focus blurry stars and smudged planetary images.

The parabolic mirror brings all the rays of light to a focus at A.  Whereas, the spherical mirror brings light from the centre of the mirror to a focus at A, whilst it brings the light from the edge to a focus at B.  Providing some focussed light and some slightly out of focus light at all points between A and B.  There is no clear focus with a spherical mirror.

Yet another reason to get a larger telescope than these toys of 100 - 115 - 120mm diameter!




Something I must tell you: I was asked this question by someone who had read this guide.

My answer is simple: “There are no such things as novice needs!”

There are objects that are visible in 'small' telescopes and these same things are beyond a 'tiny' telescope - I'm here, writing this guide, telling you that those things that aren't visible in a 'tiny telescope' make up 95%+ of what you will read about and want to see.

We buy ourselves some optical equipment because we have read that we can see Saturn's rings, but once we've seen that things like that can be seen we want to see more detail, the 'Cassini Division', or the polar caps on Mars, or the belts and bands and the 'Great Red Spot' of Jupiter's atmosphere, or the Ring Nebula, M57, in Lyra -
To view these wonderful things requires at least an 80mm refractor or a 150mm reflector! Buy anything smaller and you will not be able to see these wonderful details.

Do yourself a favour, read and digest this guide and buy at least an 80mm refractor or a 150mm Newtonian and set off on your stargazing journey on the right foot.


See for Yourself:

Left Pic. - Magnification does not reveal detail.

Right Pic. - Aperture does, even at lower magnifications!



The benefit of an equatorial mounting is that you only need to move the telescope about the polar axis to follow a star as it moves across the night sky. The polar axis points to the pole star, approximately, and therefore the polar axis needs to be set to the observer's latitude.

It's easy to find your latitude using Google! For the English Midlands, for instance, that is about 52.5 degrees. Once an object has been centred in the view, lock off the declination axis (The one with the counterweight) and as the telescope is moved (With motor or slow-motion knobs) about the polar axis the planet or star will stay in the field of view without further adjustment. An Alt-Az stand, such as is found on the Dobsonian Telescope needs constant adjustment of both axes at the same time and can be frustrating to the beginner.

Left:This diagram looks a bit confusing I know.
This is an attempt to demonstrate the difference between the movement of the stars and an Alt-Az telescope. You can see that the two move in different ways. Necessitating constant adjustment of the mounting in two directions (up and right).
An equatorial mounting automatically follows the white lines.

LATER: For those who need to know just how easy it is to set up an EQ equatorial mounting, please see my other guide "How do I set up an Equatorial Telescope Mount?"

They can be a bit of a mystery for the uninitiated, but basically you point the polar axis at Polaris then move the other two axes to find and follow your object.  (The other guide explains in detail)

Altitude and Azimuth Mountings (Alt-Az).

 Alt-Azimuth mountings are very convenient and are quite intuitive.  They need little setting up and finding an object is relatively easy and straight-forward.  If you are sharing a telescope (Teaching or just having a quick look) they can be very useful indeed.  For the instruction of children they make setting up and finding objects very quick and the chance of losing their attention is lessened.  Some come with slow-motion cables that enable you to follow objects quite smoothly, however, you always have to move both axes at the same time, which can be tricky.
Sooner or later you'll probably want or need an equatorial - Then you'll be back at square one.  If you like a challenge please get yourself an equatorial and enjoy learning. 
If you want convenience, then consider an Alt-Az mounting with slow-motions.
Dobsonian telescopes are also Alt-Az in operation but don't have slow-motions.  These can be a good first telescope too. (See section later).

Should I consider a Go-To mounting?

Once you are very experienced you can consider if this type of mounting will help you. Until then please leave them alone!
These mountings have motors and computers that find objects for you from a list.  They take most of the fun and all the skill out of amateur astronomy and will not allow you to advance beyond 'telescope user'.  You will have seen lots but don't know how to find them or much about the sky because you will have had everything put on a plate for you.

If you want to learn to be an amateur astronomer and know about the night sky this is not the way to go!
There is a Go-To version of the Equatorial, which is useful once you have learnt your way about the sky.
The Alt-Az Go-To is also not suitable for astro-photography as the field rotates as you track an object smudging the detail.

In its Favour:
If you are just observing by eye and you need to share the telescope - For instance if you are observing with your children or you are teaching some aspect of astronomy to a group then this type of mounting can be useful.  You still have all the setting up to do, and hope someone doesn't nudge the tripod out of position, but you might get some benefit from being able to talk while the mounting finds the objects automatically.

Also, if you want to observe the planets in daylight (Yes - it can be done - Venus, Mercury, Jupiter and Mars are all bright enough at times).  The Go-To mounting, when it is set up correctly, can find planets in daylight and save the danger of trying to sweep the sky manually.  This is a consideration that has some merit if you think you would be trying to spot Venus on inferior conjunction!

Astro-buddies: Me (L) and best astro- friend, Paul, with his 14" Newtonian - Another nice bit of kit! The Eagle-eyed of you may notice that it is on a 'Dobson' type mounting.

(Courtesy Astrospace)





You may notice the obvious difference between the two telescopes I'm advocating. Their size!

The Newtonian is twice the diameter of the refractor (4 x the light gathering area!). This means that the 150mm Newtonian transmits about three times the light of the 80mm refractor. (It's only three times because of light losses due to reflections and the shadow of the secondary, cell and spider).

You may wonder what effect this will have on your observing. The difference in light gathering area means that you will gain one magnitude (ie. You can see about twice as many stars) with the Newtonian.

However, the surprising thing is that the refractor will under most conditions show just as much detail as the bigger Newtonian! This is because the obstructions in the light path and the open tube arrangement of the Newtonian means that the resolution suffers somewhat. The refractor, whilst not gathering as much light, will show planetary detail at least as well as the bigger reflector.

Consequently, I can recommend an 80mm refractor and tell you that it will be just as good as a 150mm Newtonian at showing detail.

If you're really interested in spotting very faint objects, (comets, nebulae, galaxies, globular clusters, variable stars and star clouds) then the
Newtonian would be the one for you. If you're interested in planetary detail, the moon or double-stars, then the refractor would be a better bet.

However, if you're interested in having a good stooge around and having a look at everything then either type would be fine! (Just buy one big enough to show you the detail you want to see).

Table: A rough guide to the differences - By no means exhaustive, but I think there are several things there that show the essential differences between the different sizes.

The objects seen in the larger telescope are visible because of the larger optics only - It really is nothing to do with magnification.



Magnification is not the be-all-and-end-all of telescopes! You can see a surprising amount with relatively modest magnifications - If you were to pin me down and say I could only have ONE eyepiece (therefore one magnification) I would choose one which gave about 150x magnification. Not 200x or 300x or even the fantastic 525x magnification - Just 150x*.
*If I was only interested in general viewing (and not just the planets, as i am) I would reduce this to 100x because then I would need a wider field of view for Deep Sky Objects :o)


Useful magnifications vary with the size of the telescope.

The larger the telescope, the higher the maximum magnification, but this is always dependent on the 'seeing' or atmospheric turbulence.

For general viewing around the heavens using our 'entry level' size telescopes (you know the sizes we're talking about!) you will require several magnifications. A fairly low power for wide field views (30x – 50x) a medium power around (80x - 100x) and a high power for normal viewing nights (150x - 175x). Above this the image deteriorates due to the atmosphere on all but the calmest nights where you might be able to employ 200x - 220x magnification - even with an 80mm refractor.

Generally you will find that you will use magnifications in the region of 50 - 150 most of the time regardless of the size of your telescope!



I have used the 9" (225mm) Refractor at the Godlee Observatory, Manchester University. We had excellent views of Jupiter at 175x magnification.


I used the 30" (750mm) Newtonian at the Amateur Astronomy Centre Nr. Bacup. And, once again, we had some lovely views of Jupiter, at 200x magnification. (See Pic. below.)


The best view I ever had of the globular cluster M13 was in a 22" (550mm) amateur owned Newtonian, at just 200x magnification.

So, to make my point: Even 'huge' telescopes utilise 'reasonable and usable' magnifications.


Why do we need different magnifications?

The objects we look at are of different sizes and sometimes we want to see the whole, and sometimes the detail. This means that we need to be able to 'close in' on something. For instance, if we want to look at the whole of the star cluster "The Pleiades" (Seven Sisters) a 6"/150mm f6 reflector would need a magnification of only 35x to fit them all in to the view - However, if you wanted to show the double star Alcor in Ursa Major (The Great Bear) then you would need a magnification of around 100x - 120x to show the double to best advantage.

Likewise, if you're interested in planetary detail, you'll want magnifications from 80x to the maximum your telescope and the atmosphere will allow. If you want to observe the moons of Jupiter and Saturn, you will only need to use 60x - 100x.

The main consideration is the atmospheric turbulence. If the atmosphere is unsettled, then you will need a lower magnification to see detail. The higher magnifications can only be used effectively when the atmosphere is calm and 'quiet'.


How do we work out magnification?

Each eyepiece (The small lens you look through) has it's own focal length (Usually printed on the side) If you know the focal length of the telescope object glass or mirror, then all you need to do to find the magnification is divide the focal length of the telescope by the focal length of the eyepiece.

Eg1. 900mm / eyepiece 15mm = 60x magnification.

Eg2. Focal length 1250mm / Eyepiece 8mm = 156x magnification.

It can be seen then that the same eyepiece in different telescopes will give different magnifications!

Eg: a Refractor, focal length 1200mm with eyepiece 10mm = 120x magnification. The same eyepiece in a 150mm Newtonian with a focal length of 750mm = 75x magnification.

Magnification is a big selling point for telescope sellers so you have to accept that they will throw in an eyepiece that is virtually useless just to give that 525x magnification claim. As long as they give other eyepieces that cover the 50 - 100 range and the 100 - 150 range you'll be OK.

But do you know what? I have noticed that once you get away from the ridiculously small telescopes manufacturers tend to give more reasonable magnifications! Quite often 76mm Newtonians come with 525x (useless), but a 150mm Newtonian will more likely have 300x as it's 'best' magnification (One that could
actually be used on the best viewing nights).
If you don't know your primary focal length you can measure the outside of your telescope to approximate (to about 1cm) the focal length.
Remove the eyepiece, wind the focuser right in, measure as shown in the diagram.
Once you know this length in millimetres, you can find magnifications easily.
Don't forget you can always buy more eyepieces to get the usable magnifications you require.

So... Following my advice further it stands to reason that to utilise the higher magnifications to the full larger telescopes are essential! A six inch 150mm Newtonian will stand 300x magnification on a really good night, but an eight inch 200mm would be able to deploy 400x on very still nights.

Logically, then: If you buy smaller than my recommended size you won't see the detail that's available. You can really only expect to use magnifications up to 50x per inch of aperture for Newtonians, and 100X for refractors. (To be 'scientific' let's use millimetres!)

THE MAXIMUM USEABLE MAGNIFICATION on a very good seeing night is:
About 2x per millimetre diameter for Newtonians (Half that on a normal night!)
About 3.75x per millimetre diameter for Refractors. (Half that on a normal night!)The Magic Sizes!



The atmosphere is a major player in the 'What's the highest magnification I can use?' debate.  The rule is to use the highest magnification that still shows a steady clear image.
Sometimes the atmosphere is really steady and you can use the highest magnification your telescope will allow.  But, more often, there will be warm and cold currents churning up the view.  In that case you have to moderate your magnification so you can see the best view you can get.  This usually means that you have to use a maximum magnification of about 150x on a 150mm Newtonian telescope, one that boasts a maximum of 300x.

When I went to live in Lanzarote, I was looking forward to 300+ clear nights a year, but what I didn't realise was that the atmosphere would boil from sunset until four a.m.  The views before midnight were nearly always rubbish!  The best viewing was before dawn once the ground had cooled down.
In temperate latitudes we have it a bit better.  The atmosphere in the UK is usually good after the Sun's been down an hour, getting very good after midnight any time of year.  Once the atmosphere is calm you can regularly use half your telescope's maximum magnification.  On really clear and still nights you can observe at the max.
A slight mist can sometimes be a good thing - It can act like a filter when looking at the bright planets or the Moon and actually enhance the image! Clouds can be observed round by looking through the gaps.  But rain is a definite no-no.



Following this statement above it can be seen, and I hope I'm not getting too mathematical, that the maximum magnification you should use on a 60mm refractor on a normal seeing night would be 112x and on a 76mm Newtonian, just 76x. (On a NORMAL night you can use up to half your maximum magnification remember!) Anything higher than this is 'Empty Magnification' and shows you nothing more!

We have already seen that the planets are best seen at around 150x up to 300x, on a very still night. This means we NEED a bigger telescope to handle these magnifications successfully.
ie: A Refractor of 80mm or Newtonian of 150mm - The
magic sizes I recommend!
(See, I haven't just plucked these sizes out of thin air :o)

You cannot change the laws of physics!

Being able to deploy the higher magnifications usefully depends on the atmospheric turbulence and the size of the telescope. 

On some nights your telescope will be able to employ the highest magnification usable (About 100x per inch of aperture for refractors and 50x per inch for Newtonians) so the bigger the telescope, on these occasions, the higher magnification can be used.


How Did I Learn the Inadequacies of a Tiny Telescope?


In 1977, my parents bought me a 60mm diameter refractor for Christmas - I thought I knew better than the books I'd read and I'd pestered for this particular telescope... It had an Alt-Azimuth mount, no finder and four set magnifications: 15x 30x 45x 60x... And with that telescope I learnt, very quickly, that you can see a few things, but not enough!

 Left: My Astral Telescope: £55 A week's wages in 1977.

Since that enlightening Xmas, and through the last forty years of observational astronomy with some brilliant telescopes, I have been of the opinion that it is a good idea to start off in astronomy with a telescope that will show you more than the very basics. (Does it show?)

Yes, a tiny telescope will show you A FEW things, but why bother with this first step?

When I started off in this hobby you could only get these two types, Refractor & Newtonian Reflector (Nevertheless, they are still the best for starting out) - There were no Maksutovs, no Schmidt-Cassegrains, no Catadioptrics, and even a simple 6" Newtonian was £400 bought new! The only option was to buy a telescope we could afford - a 60mm Refractor on a useless AltAz tripod for £55.

Nowadays, there is a wealth of different kinds, and the prices have come down massively. So - why would you suffer the tiny telescopes when decent sized telescopes are available for you at very reasonable prices?

You're looking for a Refractor 80mm and larger... Or a Newtonian 150mm and larger...



Please DO...

Look out for fantastic bargains on eBay.

Second hand is as good as new with most astronomical instruments as they very rarely sustain damage. Just make sure that the seller will sell for the low price these instruments attract (Why they don't use a reserve price I don't know!)

Grab a bargain...

This 100mm Refractor sold on eBay for £100 - WOW!


BUT: Please DO NOT...

Be tempted to buy any telescope SMALLER than the sizes mentioned above or you will not see the detail that you expect.

Left: This tiny telescope will not begin to satisfy even your most basic astronomical needs.


TINY: Even these won't REALLY do!

These two telescopes look very impressive with their EQ mountings and slow motion knobs... and they're appealingly cheap!

But don't be fooled - They won't show you all the sights you're expecting.




I get quite a few messages asking what else you should buy to get started in astronomy when you get your new telescope.

A Good Star Atlas.

The most useful thing you can get is a good star atlas. I recommend two publications. Peter Lancaster Brown's excellent introduction to visual observing 'Star and Planet Spotting' (Available second hand on eBay from 60p) and for those who have some experience Wil Tirion's 'Sky-Atlas 2000.0' which shows stars down to magnitude 8 (A real must for those with telescopes above 150mm) Which you can pick up for rather a lot more (Mine was £30 when I got it in 1981).

Left: My two superb reference works.

Left: My SkyAtlas 2000.0 is an invaluable tool for finding anything you need to see.

A superbly detailed star atlas it shows stars down to magnitude 8.
It has 26 maps of the night sky with colour-coding.
The Orion area of the winter sky shown left. (Note Orion Nebula Enlarged at left showing magnitude 10 stars).

Left: My copy of Star & Planet Spotting is invaluable as an observer's reference. It gives lots of useful information on the Constellations, Observing the Planets, Variables, Comets and Meteors. There are also basic and very usable star chart pages in the middle. They show stars down to magnitude 6.
The winter sky, including Orion, shown left.

I would recommend that every amateur astronomer should have a copy!


PC Based astronomy programs.

It is also very useful to use a computer based program such as 'Stellarium' (invaluable Free download). There are many different ones but for now why not try a free one?

This will, after a bit of playing about with the options, equate you with the way the sky moves. You can set specific times or view the sky as it presently is. Move forward or backwards, in time, at varying speeds. You can zoom in, use a telescope or have a whole sky view! You can get information on any object. You can look at how the planets move and work out where and when to see specific things. You can turn various useful things on and off: ecliptic, planet orbits, EQ grid, Alt-Az grid, labels, ground, atmosphere, daylight, clock, constellation lines and art!

It's easy to set your location so you can see the exact sky where you are, and easy to change it so you can see the sky for where you will be going on holiday for instance! Lets you see the Southern sky or work out which stars are visible from various latitudes. It's a lovely program visually, and is worth a look. It will never replace the star atlas for usefulness 'at the telescope' - But it is invaluable for seeing how things work and planning your observing sessions.

Laptop View: Screen-shot 'Stellarium'. Orion area again with Betelgeuse selected, view South with atmosphere, daylight and ground selected. Equatorial grid is on. Constellation lines are off.


What Might I Need Equipment wise?:

It is always handy to have a pair of binoculars. They really are almost a must to accompany your telescope. Almost any size will do, except the tiny sports types. Binoculars are 'sized' by their magnification and their diameter. For example, a pair of 10 x 50 binoculars give a good view. They magnify 10x and have lenses 50mm across and are referred to as "Ten by Fifty" (not 'Ten times Fifty'). Personally, I have a pair of 8 x 40 binoculars. They have a slightly wider field of view (Because of the lower magnification) and are lighter and easier to hold steady (Because they are smaller).

Binoculars will help you find the exact position of the bright galaxies, check quickly on the position of Jupiter's moons (Oh, yes, don't let the claim that a telescope will show Jupiter's moons be a selling point – If it wasn't for the proximity of the very bright Jupiter you could see them without a telescope!) With your binoculars you can see all the planets out as far as Neptune, and they give many wide views of the milky way. They are useful tracking down the Messier objects too. I would recommend you get a pair of 8 x 40, 7 x 50, or 10 x 50 binoculars.

Bino-Bargain: My excellent 8 x 40 wide angle view binoculars cost me a tenner!
Note the size shown on the right hand side.

Try to keep things simple - No huge magnifications, No Zoom Eyepieces and make sure you check the size - Lots of misleading sizes advertised on eBay!
Whilst the 60mm and 70mm and even 80mm binoculars are very nice for astronomy, you do need a tripod and mounting to hold them steady. The main object of using them in conjunction with your telescope is for conveniently looking at something before observing. It's not very convenient if you have to use a tripod! By all means get a large pair for use with a tripod if you like the views - But this would be an instrument in its own right and not really used for a quick check prior to observation with the telescope.

For your telescope:

Buy nothing extra for your telescope until you are familiar with using the telescope you bought. It's very easy to spend lots of money on things that you don't or won't need.  Take your time to get used to your instrument and your view through it.  After a while you will realise what you need.
The next thing you'll probably want is another eyepiece to extend the range, sometimes higher magnification and sometimes lower.
Barlow Lens

It can be beneficial to get a 2x Barlow lens. This is used in conjunction with an eyepiece, not on its own.  This device effectively (optically) doubles the focal length of your telescope and therefore all your eyepieces can be used as they are or in unison with the Barlow to give twice the magnification.  
Sometimes useful but not always - Remember the magnification limit of your telescope and try not to exceed it.  Try not to duplicate magnifications (Waste of money) if you buy a 10mm it will give you a magnification. Adding your Barlow will give you another magnification twice that of the first.  If you then bought a 20mm eyepiece adding the Barlow would duplicate the magnification you get without it using the 10mm.  Always take care you won't duplicate.

Using a Barlow also means that if you have a refractor of f10 you will be using it as though it is an f20 with the resultant shrinking of the apparent field of view and 'photographic slowing of the system'... Care is needed and I wouldn't spend a lot on a Barlow unless you can try it first!

Another important part of the telescope is the 'Finder Scope'.
This is the smaller telescope attached to the side of the main scope that allows you to locate things in the eyepiece. You can adjust the finder's cross-hairs to precisely line up with the centre of the field of view of the main scope, even at high magnifications. It can be tricky, but you can't really do any harm. Lining up the finder should be done with a distant earthbound object in the daytime so time can be taken to get it spot on. The more accurate the finder is set up the easier observations will be in the dark.
Some finders that are supplied with telescopes are woefully small for the telescope they serve. A finder of at least 25mm is recommended and 30mm is much more desirable for 150mm and a 50mm finder-scope for 200mm reflectors.

Eg: If you're hoping to line your telescope up on Neptune, you have to bear in mind that the planet is magnitude seven or eight and to find it easily in the finder, the finder has to gather a good deal of light too! (The 70mm Refractor I review later in this guide had a finder of just 15mm diameter - Couldn't see much of anything fainter than Jupiter!)

If you can replace this small finder with a big, 'straight through' finder (The right-angle finders are difficult to use for the beginner) your observations will become much easier.

The finder needs to gather light and show stars that cannot be seen by the unaided eye. Some scopes come with something called a red-dot finder. This should be replaced with a light gathering magnifying finder to enable you to see things that your eye can't. What use would a red-dot finder be in locating Neptune when it is Magnitude 8 and your eye can only possibly see to magnitude 6? You need a proper finder...

Left: Red Dot finder types in common supply.
These won't show you anything you can't see with your eye!

These were designed to help Go-To telescopes sight on the bright stars.  They became the 'cheap' option for beginners to look at bright objects only.  You'll want more than that!
Left: A Proper Finder-scope - 6 x 30mm
This will show objects down to magnitude 8 or 9. You can line up better because of the magnification and cross-hairs.


Do not pay any extra money out for a 'Moon Filter' - No self respecting amateur astronomer would use such a gimmick (You cannot harm your eye with the moon's light!).

It can be bright but if you're looking at the Moon then there's no need for dark adaptation - Astronomers spend most of their time trying to maximise the amount of light available to the eye - Why would you darken the image? Each time the light passes through a lens or filter there is some loss of light and there is some degradation of the image - Leave it out and see more of what's there!

Honestly: Unless you have a 250mm (10") telescope or larger... This is where your Moon Filter fits for best results.



As you learn more about the things you're looking at you'll get an idea of the direction you would like to go and decide what your favourite types of astronomical object are.
At that point, because you will have learned more as you progress, you will know what you need to get next to improve your viewing of your particular area of interest.

Different areas of astronomy require different equipment. You've read about needing a big Newtonian for Deep Sky objects, and the planets are best seen through a large refractor. These are the kinds of considerations you will learn to apply to your future optical equipment planning.
Also, as you read more, talk to people and learn about astronomy, you'll come across other types of telescope.  Some of these are very well suited to specialisms.  In particular and worth a mention here is the Maksutov catadioptric telescope.  Absolute wonder on the planets!  However, I would still not recommend a beginner to start here, but according to Paul Money, the BBC Sky at Night equipment reviewer, there is no better telescope than the SkyWatcher 180Pro for observing the planets - But my advice for the beginner is: Get yourself some experience with the simpler telescope types before overcomplicating it for yourself!



Travel Scopes:

You may find that your telescope is a bit big for just grabbing quickly to have a look at something, or it won't fit in your car with all the family when you're off to the seaside but you'd like a telescope in case you need to observe something. You could do worse than get yourself a 'Travel Scope'. This is an easily portable telescope designed for use on the go.

A travel scope should not be considered for your Main telescope, but will complement your Main telescope. There are plenty of short focus refractors in decent sizes that will still show you plenty when you're out an about. For instance I have an astronomy acquaintance who takes his in a back-pack when walking his dogs and sets up while they have a run about on the beach.

You can get a very good 70mm Travel Scope for around £50 new (Including the carry-bag).

The 70mm objective lens gives enough detail for casual observing and the f6 ratio gives a wide field and bright deep sky images too. A good all rounder of a decent size. (Please resist buying anything smaller than this even as a second telescope!)

You may have to buy a short focal length eyepiece (4mm) or 2x Barlow or even a 3x Barlow to get decent planetary image size (100x Magnification and above) as some come only with 20x and 40x magnifications which, while refreshingly conservative, are nowhere near enough to show detail on the planets.

Handy: a 70mm Celestron Travel Scope on extending tripod with carry-bag. Ideal for 'Astronomy On-The-Go' but should not be your main instrument, unless as a 'stepping stone'. These can be had for around £50 new! 

The travel scope should not be considered as a starter scope if you are interested only in the planets as the image is too small. These scopes are excellent for having a good look round the wonders of the universe and getting a feel for what can be seen with a 'proper' instrument (But will let you down on planetary views).

Resist buying the reflecting types of travel scope at all costs! They are far too delicate for true travel scoping! Refractors are much sturdier.

If you have limited funds and want to get into astronomy with a useful instrument, this is a great way. By getting started with a 70mm Travel Scope you are able to spend very little and have a scope that will be of use, even if you do 'take the plunge' and buy a larger telescope in the future - It's always a good idea to have a small, easily used telescope handy!

This telescope is great for most aspects of astronomy 'on the go' and having a quick look around the night sky, but, once again, I wouldn't recommend it for your main telescope, although I must admit that it would have been much better than my first 60mm instrument! (You know why... Think about it... That's right, it's a bigger diameter lens! - More light and more detail.)

These are wholly unsuitable for even basic astronomy due to their very short focal length and spherical mirror. The image in all but the lowest magnification is blurry at best.  The mirror must be parabolic to bring all the light to a focus at one point.  These telescopes have typical appertures of 76mm and focal lengths of 300mm - Not good enough for us astronomers - Steer clear!



The most important thing you need... Patience!

Being able to 'see' with your telescope is something that is helped by the size of your telescope, but also needs a lot of experience. Start off with the magnifications I have suggested and keep observing. As you get used to seeing objects in a telescope you'll learn to really 'see' the detail that's there.

It might sound like I'm trying to put you off but actually I'm hoping that you'll realise that what I'm saying is, if you're initially disappointed with your telescopic view of the heavens, stick with it and you will gradually be able to see more and more.

Someone like me, who has spent years looking through telescopic equipment, can see a whole lot more than a raw beginner and somewhat more than someone with a year's experience. But this is a fantastic hobby and there wouldn't be much fun if everything was there on a plate for you straight off!

Most of the fun of this hobby is gradually learning more and more about the universe and learning to see it for yourself.


The Dobsonian Telescope: Surely that's a Newtonian too?

I think a quick word about Dobsonian telescopes is in order. Having had John Dobson as a house guest when I lived in Horncastle, when he gave a lecture at the Horncastle Astronomy Weekend, I think I am able to provide you with informed information on this variation on the Newtonian telescope.

The original design was for a large aperture telescope, using the Newtonian layout.
The mounting is a simple altitude and azimuth non-equatorial design (ie. up and down left and right).

The beauty of these telescopes was that the mirror could be made from much thinner, cheaper glass than the standard Newtonian because it was on an Alt-Az mounting and not an equatorial. The mirror was supported on bubble-wrap, cardboard float points and a 'sling' type support strap! The complicated mirror cell and thick glass mirror of the equatorially mounted Newtonian was avoided and much bigger telescopes became affordable to amateurs.

John Dobson and Paul Money at the HAW: Paul's 14" Newtonian on the 'Dobsonian Mounting' can be seen behind them. (Courtesy Astrospace)

Although these telescopes are fantastic to use, in the hands of someone with little experience tracking the object is tricky and high magnifications are impractical. Consequently, planetary observation can be difficult for the beginner.
I would respectfully suggest that the Dobson / Dobsonian telescope should be avoided until you get some experience with the standard 'equatorial mounting'.
Unless: You are only interested in Deep Sky, whereby you will not need very high magnifications and the Dobsonian Reflector will be easy to use and will give excellent views of Depp Sky Objects (DSOs).  The Alt-Az Dobsonian mounting is quite intuitive to use and can simplify your learning in the early stages.
However: If you want to have high power views of the planets, do not consider the Dobson telescope. You will need an equatorial to allow easy tracking.


NOTE: The term Dobsonian has come to mean a reasonably large Newtonian on a Dobsonian type mount.  They don't have the strap and bubble-wrap support, or the thin mirror that John designed.  Nevertheless, it's a convenient way of describing the layout.

These days there are many Dobsonian telescopes on the market.  You get a lot of apperture for your money and the views of Deep Sky objects are wonderful on low to Medium powers.  If you'd like to go down this route it's something that you will have to think on.  My own recommendation is to start with an Equatorial instrument, but I can see that for a breathtaking view the Dobsonian telescope deffinately has something to offer.


What about "Catadioptric Newtonian" Reflectors?

There are a number of companies now selling 'Catadioptric Newtonians'. I would suggest that these are to be avoided by the beginner.
This is NOT the same thing as a Maksutov/Cassegrain or Maksutov (These are known as Catadioptric Telescopes because they use both mirrors and lenses to form the image) - These are excellent instruments that rival a refractor of the same size in their image detail. 
The only reason I don't recommend them to beginners is the expense!
(They are pricey but excellent even in 80mm sizes.) If you think this short-tube long focal-length instrument might be the one for your planetary observations, please get in touch and I'll help you choose. :O)
Ahem... Back to 'so-called' Catadioptric-Newtonians...
These hybrid telescopes have optically extended focal lengths - Why?  I really don't know! - So you'll find a short tube but with a focal length of typically 1400mm. (The telescope will look on the outside like the telescope shown at top section on Newtonians (a 750mm f5), but may state 1400mm f10). The view in these telescopes is narrow and unless the mirror is very good the image quality will suffer.

There are two types: The better designed ones use an optical 'corrector plate' which is a thin lens at the tube aperture and are 'sealed systems' (See picture below) - Others use a Barlow lens in the focuser and are not closed optical systems.
Avoid the latter: If you are going to do this you might as well generate some benefits! Leaving the tube open and continuing to use a standard spider is not a clever way of doing it! Get a good quality scope with a corrector plate and reap some benefits.

To be fair to the closed tube Catadioptric-Newtonian telescopes: There are three advantages over the simple Newtonian: The tube is closed by the corrector plate and this eliminates tube currents, this lessens the tarnishing of the mirror surfaces, and thirdly, the secondary cell doesn't need a spider to hold it in place, so there is not as much diffraction of the image (But it's still there).

Cat-Newt: Closed tube Catadioptric-Newtonian. The best way to configure this system. Note the 'corrector plate' holding the secondary in position.

Buyers make sure: The main mirror and the corrector plate must be very good quality as the optical lengthening of the focal length means that any errors in the mirror or plate are magnified!

A well made quality Catadioptric-Newtonian of 150mm could be an excellent instrument for observing the planets. If your interest lies in this direction you could consider this as an option but make sure of the accuracy of the main mirror and the corrector plate.


A Word About Telescope Merchandising Codes or Naming Systems.

The codes used by manufacturers to describe telescopes usually relate to the various sizes and focal lengths mentioned above: There is a sort of de-facto system that a bit of logic will unravel.

A telescope called 'StarPlod
70070' will be 700mm focal length and 70mm Diameter.

One coded 1200/150 will be 1200mm focal length and 150mm Diameter.

60/900, you guessed it, 900mm focal length and 60mm D.

What about a '3003' ?
This company is selling a
30" focal length with diameter 3" lens (f10).
Trying to catch us out!
Make sure you check any code against the description.



Some telescope sellers / companies:

Obsessed as they are with magnification - They will advertise a magnification as an AREA compared to normal view. This means where we astronomers would say a telescope magnifies 50x they may claim 2500x Which is 50 x 50 = the difference in the area. This doesn't happen often nowadays, but watch out.

You won't be fooled by this because you know that magnification from 25x to around 150x is all you need for most objects.

Sometimes they are selling just the telescope without a mounting. You WILL need a mounting, and an equatorial mounting at that! Make sure it's the whole telescope and the mounting and not just the optical tube assembly ('OTA')... watch out.


So... the telescope that I found called a PlanetViewer F90076 is a Newtonian reflector, with focal length 900mm, and diameter 76mm (2.99") which, as you can now work out is f11.8 (Newtonian f11.8... Eek! Wobble wobble, very dim image, very narrow field of view like looking up a straw!)

Which is a little less than half the recommended MINIMUM size - Which will perform, I'm sorry to say, approximately a QUARTER as well!

Don't forget that a Newtonian reflector operates, detail wise, as well as a refractor of half the size - Would you really buy a 38mm refractor to do amateur astronomy? Of course not!

Smudge Saturn: Close up!

This image is representative of a 76mm (3") Newtonian reflector or a 40mm (1.5") refractor image at 100x.

I JEST NOT dear reader... Please be guided by the voice of experience :O)


IF some well-meaning soul has bought you a 'tiny telescope' for a present, and having read this guide you know they have bought you something that will fall short of the ideal.


Message me and I'll give you some advice.

Owning a tiny telescope is not the end of astronomy but you have to accept the limitations.

It's not ideal to own a tiny telescope, but there are some projects you can embark upon that will help you appreciate your next telescope and help you to 'see'.

(And I'm not being sarcastic - There is no rubbish-bin involved :o)

MY RECENT RESEARCH. In the interests of checking the accuracy of my claims I bought a 70mm f10 Bresser EQ Refractor (off eBay, naturally!).

As you know by now this is slightly smaller than my minimum recommended size by 10mm. I did extensive observations of the planets (Jupiter, Saturn, Mars) stars (Albireo, Alcor, Double-Double) and Messier objects (M27, M13, M29, M11) with an aim to either corroborating or re-calibrating my 'minimum' telescope size for you. I feel that I must tell you that this telescope performed well.  The detail on the planets was enough to allow a beginner to have the WOW moments.  The stars split were as good as you might expect (Double-Double was only two stars in this small telescope).

The Findings:
The 5x20mm finder was too small to show objects below magnitude 8. Not brilliant, but adequate (You really need a 30mm finder of good quality).
Really a 25mm finder is the absolute minimum you need to show the objects you're looking for (50mm diameter on telescopes over 150mm). See finder scopes section under 'What else will I need?' section above.

The eyepieces supplied were not the best but gave reasonable images without defocusing towards the edge..

The planets were well seen even though quite small image scale.  Detail could have been better, but the 70mm objective performed well overall.
So, I would say that if you really can't stretch to an 80mm refractor, then you can get some good views with a 70mm telescope.

At least we know where we stand!

Adequate: Bresser 70mm f10 Refractor on EQ mounting.

I must therefore duly report that, following my research experiment, my assertion that an 80mm refractor is the smallest for good results for the beginning amateur, but reasonable results can be had from slightly smaller telescopes :o)

"The Watch-It Gallery" - Who would buy these?


Get to know what a telescope looks like when it is set up. If you come across a telescope that is being advertised (EG on eBay) and the 'scope is obviously upside down, or assembled in a totally whacky manner - Please leave it alone!



You may laugh, if you don't you need to learn a bit more about how to set up a telescope, but seriously, these telescopes could have sustained serious damage being upside-down!

Check and double check - Before buying.

No answer? Move on, buddy!

I came across this telescope on eBay whilst looking for a SkyWatcher 150mm Newtonian telescope for someone... This telescope was advertised as a 150mm Telescope.

This is NOT a 150mm SkyWatcher!

It's a 130mm SkyWatcher - To the expert the difference is obvious. To the beginner, you could end up paying rather a lot of money and ending up with something substandard.

I tried contacting the seller, but no joy. The answer there is to walk away quickly and look elsewhere.




SkyWatcher make the only 130mm Newtonian I would recommend.  SkyWatcher make excellent telescopes and their 130P EQ2 model is smaller than I usually suggest for the beginner, but if you really can't afford a 150P EQ2-3 then this might have to serve!  The optics are parabolic, which means that you'll get the best view you can from such a small telescope. (Make sure it's a 130P if you have to get one of these!)  The mounting, just as the scope itself, is well designed and constructed. 


There is a very good reason that so many people are selling their tiny telescopes - It's because tiny telescopes are no good for astronomy!

  Further Reading:

My other telescope guides may interest you:
Setting Up an Equatorial Mounting (Simple!)

Best Value Planetary Telescope  (90mm Refractor)

Best Value Beginner's All-Rounder Telescope  (130mm Newtonian)



I will answer as soon as I can and it's no bother – Honestly!
If you buy smaller than this you will sell yourself short of the experience you deserve!


Clear skies and good seeing... I hope this guide has been useful. :o)

All text and images © Barry Cooper 2008-16 unless otherwise credited.



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