You can get an instrument capable of giving years of good astronomical views for
around a week's wages... Read on!
I REVIEW AND UPDATE THIS GUIDE REGULARLY
Last Updated - May 2020
Elements of this website first published by me 2010.
"There is a very good reason that so many disgruntled people are selling their tiny telescopes ...
...It's because tiny telescopes are no good for astronomy!"
In this guide: 20+ Photographs / 30+ Illustrations / 2 Videos
The two types of telescope I am going to recommend are: 'Newtonian Reflector' and 'Astronomical Refractor'. I will generally refer to them as Newtonian and Refractor, to save confusion between reflector and refractor.
These two (left) are impressive looking instruments, with their equatorial mountings and slow motion controls, but they are too small to be of any real use in amateur astronomy. You will need something slightly larger to see what you will read about and want to see.
Although, technically, the 120mm Newtonian should be at least equivalent to an 80mm refractor (See 'Resolution' section later) this model has a spherically figured
mirror (see 'Parabolisation' section later) and would not produce images as good as an 80mm achromatic refractor. The smallest Newtonian I recommend is a parabolic 130mm
(Search "130P" or see Newtonian Reflector section below).
The reason I recommend only the refractor and the Newtonian telescope types is that these are the two best suited to the beginner. This is the case 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. Please read on to get information on the size of telescope you need to see the things you want to see.
There is also an information section covering other types of telescope that you may have come across, for those that are interested. However, the beginner is recommended to get either a refractor or a Newtonian, dependendent on your interest.
If you were only interested in Deep Sky, even a 'Dobsonian' would fill the requirement.
You can see a good number of astronomical objects with smaller instruments - Any optical aid is better than none - But, if you are setting yourself up for a good look around the sky, and to see if amateur astronomy is for you, why start off on the minimum? Good telescopes are available at very rerasonable prices and you'll get a lot more satisfaction out of your instrument and move further on in the hobby before you have to 'upgrade' if you get a decent instrument to begin with!
Please read on to discover which type and size you need. I have called this 'Complete Essentials' because you really NEED to be aware of all these things when
considering which telescope is the right one for you.
Above: My Phenix 127mm (5") f10 Astronomical Refractor - A very nice bit of kit that cost me £90 second hand. (Bargains are out there once you know what you're looking for). This telescope was just about the best refractor I've ever used. Beautiful images of stars and great detail on the planets too.
Although I recommend 80mm as the smallest size refractor telescope - There are some very nice 90mm telescopes that are not that much more expensive and are so much better! - These represent an excellent, rather than bargain basement, start to astronomy.
SkyWatcher 90mm (3.5") f10 achromatic, equatorially mounted refractor: New price in UK is about £169 (April
If the 90mm is still too expensive and you really can't manage to afford one - A 70mm Capricorn achromatic, equatorially mounted refractor might have to suffice (if you really can't manage the extra £55 to get a really great telescope!) as an 'entry level telescope'.
New price in UK is about £115 (April 2020).
My advice, though: Please SAVE UP for the 90mm! If you have the will to wait, you can
get a superb 90mm telescope.
The Refractor uses a large lens, the object glass, to collect and focus the light to a point. The image at this point is examined by the use of an eyepiece. Different eyepieces magnify the image differing amounts.
The parts of a refractor are there to hold the object glass and the eyepiece in precisely the correct relative positions no matter where you point the telescope. It can be seen that the light rays pass uninterrupted down the tube, passing through the holes in the baffles and arriving at a focus near the eyepiece. This is a closed system with nothing in the way of the light to detract from the image.
The Dew Cap stops moisture forming on the cold glass.
The Cell, holds the lens and accurately directs the light path down the centre of the tube.
The light-tight tube holds everything in place.
The baffles help to stop internal reflections. (Not all refractors have more than one).
The focuser allows precise movement of the draw tube in and out of the main tube.
The Draw Tube holds the eyepiece.
The eyepiece magnifies the image formed by the Object Glass.
THE NEWTONIAN REFLECTOR
Above: My 150P on EQ3-2. A great all-rounder telescope. Good for Deep Sky objects but also reveals good detail on the
A very nice bit of kit that cost me £100 (Bargains are out there once you know what you're looking for).
I recommend at least a 130mm parabolic telescope - These represent an excellent, rather than bargain basement, start to astronomy.
A 150mm (6") f5 parabolic, equatorially mounted Newtonian Reflector New price in UK is about £325 (April 2020)
If the 6" is too expensive and you really can't manage to afford one - A 130mm (5.1") parabolic, equatorially mounted Newtonian may have to suffice!
A SkyWatcher 130P = New price in UK is less than £200 (April 2020).
can't afford that - Please SAVE UP! Don't buy anything smaller than a 130mm parabolic Newtonian!
The Newtonian uses a mirror to focus the light by reflection. (Ideally this mirror should have a Parabolic figure). The light would pass out of the tube but for the secondary flat mirror that directs the light out through a hole in the tube to an eyepiece. Different eyepieces magnify the image different amounts.
The parts of a Newtonian Reflector are there to precisely hold the Primary and Secondary Mirrors and the eyepiece in precisely the correct relative positions no matter where you point the 'scope.
It can be seen that the light rays are interrupted as they pass up and down the tube, passing through the vanes of the spider and being reflected a second time by the secondary mirror (Usually between 15% and 25% of the primary mirror diameter depending on focal ratio), finally arriving at a focus near the eyepiece. This is an open optical system with air currents and obstructions along the way of the light path which detracts from the quality of the image. Because of this interruption in the light path, to get the same detail in a reflecting telescope you need a slightly bigger size to counteract the effects of the interrupted light path.
The telescope Tube holds everything in place. This needn't be a solid tube, it can be a lattice or framework, as long as the optical components are correctly positioned relative to eachother. The only thing to watch out for is stray light getting into the eyepiece, to avoid this on skeleton and lattice tube Newotnians, there is usually a box or tube section where the focuser is fitted.
The Cell holds the parabolic Primary Mirror and has adjustments that direct the light precisely down the center of the tube toward the secondary mirror.
The Secondary Mirror is perfectly flat and directs the light at 90 degrees out of the tube to the correct point near the eyepiece.
The Spider holds the secondary mirror mount, which itself can be precisely adjusted to bring the light to the correct focus point.
The focuser allows precise movement of the Draw Tube.
The draw tube holds the Eyepiece in the correct position to view the image.
You can imagine, therefore, that the Newtonian is a slightly more delicate instrument than the bomb-proof refractor and should be handled more carefully and the alignment of the mirrors checked periodically. Aligning the mirrors correctly is called 'collimation', and makes sure the column of light passes down the very center of the optics.
You may be interested in other types of telescope. I will indulge your interest... a little.
The Dobsonian Mounted Telescope
(For your information)
This type of telescope uses precisely the Newtonian optical layout.
This type of telescope comes on an Alt-Az mounting which does not follow the stars. It is easy to use with low to medium magnifications, however, tracking an object at high magnifications is difficult for the beginner. I would only recommend a Dobson mounted telescope for a beginner who was despirate for light-grasp and Deep Sky Object observation as they can be cheaper than smaller equatorially mounted scopes.
The Dobson mounted telescope is intuitive and it's easy to line the telescope up on an object. Following it can be simple enough at low to medium powers. The telescope comes off the mounting easily for transportation and storage. Setting up doesn't take long and the experience can be less challenging.
Above: John Dobson with a 12" Dobsonian Telescope.
Recommended for the beginner if your interest is soley in Deep Sky. The easy use mounting and easy-peasy set-up is intuitive and natural. At low to medium magnifications these telescopes give great images and can be recommended for Deep Sky fanatic beginners.
MAKSUTOV-CASSEGRAIN (For your information)
This type of telescope has spherically figured optics and consists of a spherically figured meniscus lens at the front, the spherically figured main mirror and a secondary mirror spot (aluminised onto the inner surface of the meniscus lens). These telescopes are sealed tube instruments, typically f11 to f15 in focal ratio. Consequently, they have quite narrow fields of view, ideal for planetary, lunar and double star observations. Unfortunately, because of the high focal ratio, Maksutovs don't do very well with Deep Sky objects.
I avoid recommending them to beginners because of the relative expense. They are excellent telescopes and can be treated as very similar in performance to a refractor of the same diameter, however, because they have a folded light-path, physically, they are very much shorter than an f15 refractor of the same diameter.
The f12 SkyMax127 in this picture has a focal length of 1,500mm in a tube less than 400mm long. It gives planetary images equivalent to a 150mm Newtonian on the best nights, it will rival a 130mm Newtonian on any night.
Maksutovs, like refractors, take longer to cool down to become optically excellent, because they are sealed optical systems.
The Maksutov-Cassegrain is a sealed unit and consequently the only parts, like the refractor, that we come into contact with are external.
The light passes first through a spherically figured Meniscus Lens (Thicker at the edge) and falls on the spherically figured Primary Mirror. This reflects the light back up the tube toward an aluminised spot on the back of the Meniscus Lens which reflects the light back down the tube to the Eyepiece.
Focusing in the Maksutov is done by moving the primary mirror. The focusing knob is found on the back plate and not the draw tube in this design.
The telescope Tube holds everything in place. This must be a solid light-tight tube, it can't be a lattice or framework.
The mirror support holds the spherical Primary Mirror and has adjustments that direct the light precisely down the center of the tube toward the secondary mirror (This is set at the factory).
The Secondary Mirror or 'Spot' is a small aluminised circular zone (usually between 16% and 20% of the diameter) on the back of the meniscus lens and directs the light back down the tube to the correct point near the eyepiece. The light ray angle is much reduced so optically increasing the focal ratio.
The tubular Baffle stops stray light from the meniscus lens, other than that from the 'spot' entering the eyepiece.
The Draw Tube holds the Eyepiece in the correct position to view the image.
The Focuser knob on the back-plate allows precise movement of the Primary Mirror to affect focusing.
Maksutov-Cassegrain: Not recommended for the beginner on price! - If you're not sure about astronomy, spend little first! (See above types)
Pricewatch: New equatorially mounted SkyWatcher Skymax 127, Maksutov-Cassegrain f12 = £420 (April 2020)
SCHMIDT-CASSEGRAIN (For your information)
These telescopes are externally similar looking to Maksutovs. They too have a corrector plate but have a different optical configuration. Optically they have some inherant field curvature problems and are even more expensive.
This type of telescope has spherically figured optics and consists of a corrector plate at the front, the main mirror and a secondary mirror. They are sealed tube telescopes, typically f10 to f12 in focal ratio and have quite narrow fields of view, ideal for planetary observations. Consequently, Schmidt-Cassegrains don't do very well with Deep Sky objects.
I avoid recommending them to beginners because of the relative expense. They are good telescopes and can be treated as very similar in performance to a Maksutov of the same diameter, however, because they have field curvature problems they don't quite stack up to the refractor of the same size.
The Celestron C5 Schmidt-Cassegrain f10 127mm in this picture (Image Courtesy: 'Celestron') has a focal length of 1,250mm in a tube less than 350mm long. It gives planetary images equivalent to a 130mm Newtonian on the best nights, it will equal a 120mm Newtonian on any night. Schmidt-Cassegrains, like refractors and Maksutovs, take longer to cool down to become optically excellent, because they are sealed optical systems.
The Schmidt-Cassegrain is a sealed unit telescope and consequently the only parts, like the refractor, that we come into contact with are external.
The light passes first through a Corrector Plate and falls on the spherically figured Primary Mirror. This reflects the light back up the tube toward a Secondary Mirror housed in its own cell set into the corrector plate. The Schmidt-Cassegrain has the largest obstruction to the lightpath of all reflecting types. The Secondary reflects the light back down the tube to the Eyepiece.
Focusing in the Schmidt-Cassegrain is done by moving the primary mirror. The focusing knob is found on the back plate and not the draw tube in this design.
The telescope Tube holds everything in place. This must be a solid light-tight tube, it can't be a lattice or framework.
The Baffle is tubular and stops stray light from the corrector plate being seen by the eyepiece. Only light from the secondary can enter the Draw Tube.
The mirror support holds the spherical Primary Mirror and has adjustments that direct the light precisely down the center of the telescope Tube toward the secondary mirror (This is set at the factory).
The Secondary Mirror, supported in its cell (Usually between 27% and 35% of the diameter) directs the light back down the Tube to the correct point near the Eyepiece. The light ray angle is much reduced so optically increasing the focal ratio.
Focusing is achieved by a knob on the back-plate that moves the Primary Mirror inside the telescope.
Schmidt-Cassegrain: Not recommended for the beginner on price! - If you're not sure about astronomy, spend little first! (See above types)
Pricewatch: New equatorially mounted Celestron VX5, 127mm f9.8 Schmidt-Cassegrain f12 = £1,344 (April 2020)
So now we move onto the detail behind my size and type recommendations.
Buckle up - There's a lot to consider!
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 can only see stars of a given minimum brightness with a telescope of a given aperture. Bigger telescope = More detail & Dimmer star
limit. Some telescope companies state things like, 'Collects 250 times as much light as the human eye,' in their adverts. This sounds like a gimmick, but actually it's a very good
point. Light gathering power is dependent on aperture minus any obstruction.
If you like to think in terms of multiples of the human eye that's fine. (which is pretty standard at 7mm diameter = 38.5mm squared, fully dilated).
Just be aware that the eye is a funny thing and twice the light doesn't look twice as bright!
The eye has a pretty standard performance...Eyeball Performance: Resolution 'R' = 3.0' Magnitude limit = 6.0
This is enhanced by the use of optical instrumentation.
ROUGHLY SPEAKING: Telescopes
perform on stars in the following manner:-
Diameter of Primary Resolution Magnitude Limit
30mm 1" telescope: R = 4.5" M=9.0
50mm 2" telescope: R = 2.3" M=10.5
80mm 3" telescope: R = 1.5" M=11.4
100mm 4" telescope: R = 1.1" M=12.0
5" telescope: R = 0.9"
6" telescope: R = 0.7"
telescope: R =
250mm 10" telescope: R = 0.5" M=13.9
telescope: R =
NOTE: The magnitude limit for nebulae / Galaxies is about two magnitudes less.
Star limit = Mag. 10.0
DSO limit = Mag. 8.0
NEED the BIGGEST objective you can manage (either financially or physically - telescopes get heavy!) to allow detail to be shown and faint stars and galaxies to be glimpsed, no matter the
If you use more magnification than the telescope can show, this is called 'empty magnification'. See magnification section later for more.
Go Compare: Comparing the refractor views close up! (View in 50mm on the left, 90mm on the right in this comparison).
(Actually Left side Saturn image is a little bit too detailed!)
Left of image: Approx view of Saturn with 50mm (2.0") refractor or a 80mm (3.1") Newtonian.
Right of image: Approx view of Saturn with 90mm (3.5") refractor or a 130mm (5.1") Newtonian. (I'm happy with this image representing a really still night!)
There are two main considerations: Splitting binaries 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. (Close pairs of stars cannot be split with tiny telescopes or higher magnifications)
Left is a 20x view of the Pleiades (M45) with a 6" 150mm telescope (Lower frame).
Note: not only the many more stars in the larger telescope, but also notice 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 near the centre bright star (Alcyone) 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.
Deep Sky Objects
Left: 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).
See diagram, Left. The
double-star shown is just a connected blob, at any magnification, for any telescope under 120mm (Parabolic Newt.) or 90mm (Refractor) - Where they are just about spearate
Also: Note that as the telescope gets bigger it collects more light and the stars appear brighter in the eyepiece. More light concentrated into a smaller point!
The reason that refractors show more detail than the equivalent reflector is that there are no obstructions in their closed system of optics. The Newtonian has a spider, a secondary mirror and tube currents that degrade the image. Although a Newtonian's optics may be 'diffraction limited' (See later section) the optical system certainly is not! A refractor on the other hand can be pretty much perfect for its aperture.
For simple reckoning of equivalent sizes, multiply the refractor object glass diameter by 1.3 and you will get a good approximation
of the equivalent Newtonian primary mirror diameter. Or divide the Newtonian by 1.3 to get the equivalent refractor size. Be aware it is only an approximation - Different
manufacturers and different observing conditions can alter the perameters somewhat - But as a general rule it's accurate enough.
Proof of the pudding: I have a 130mm f5 Newtonian and a 100mm f9 refractor and a 127mm f11.8 Maksutov-Cassegrain. I can
tell you that in extensive test comparisons, all three are equal in resolution performance. However, the Newtonian 130mm f5 is better at Deep Sky than the 100mm f9 Refractor or the 127mm
f11.8 Mak. But, the closed system refractor, and Maksutov perform to their best on more nights than the open tube Newtonian! In many aspects of astronomical instrumentation it's
'swings and roundabouts'. The decision of "Newtonian or Refractor?" is something that you will spend hours thinking about. There's no easy winner!
You get to choose which view you would prefer by picking a telescope of the size I
advocate in this guide!
Authentic View Left: 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%.
When light passes through a lens the light is split into its component colours somewhat.
Depending on the type of telescope you choose or the lens it has, you will get more or less chromatic abberation. This 'false colour' shows itself around bright objects as red and blue fringes of colour.
Generally speaking, the better the telescope the less chromatic abberation will affect your view.
Reflecting telescopes do not suffer from chromatic abberation as the light does not pass through the glass of the mirror but is reflected off. All light is reflected the same.
LEFT: You will see that the different lens types have different levels of success at combatting chromatic abberation. When selecting a refractor it is important to know what type of object glass you are going to get and therefore you can be prepared for the level of chromatic abberation to expect. Newtonian buyers, you can ignore this worry (You have enough on your plates!)
An f6 refractor will have significantly more chromatic abberation than an f15 refractor with the same lens type.
ABOVE: In this diagram the percentage figures are not strictly accurate, but they do give a good idea of the relative differences between the different lens types.
The longer the focal length of the lens, the less the effects of chromatic abberation are seen. Refractors in the early days of telescopic observation grew to huge lengths to try to get rid of the 'false colour'. These cumbersome instruments were known as aerial telescopes and some were as much as 150 feet in length!
Luckily, a British inverntor called Chester Moore Hall created the achromatic lens in the 1730s, using a combination of a Crown Glass lens and a Flint Glass lens, which have different dispersion properties, to bring the red and blue light to a much closer focus.
In modern times, manufacturers have used exotic types of glass to lessen these effects yet further (But at a price! These exotic glasses aren't cheap.) I am lucky enough to own an ED telescope and I must say that the colour is very good.
Above: Pedro Ré, and his 150' Aerial Telescope. Johannes Hevelius had a similar instrument in Danzig, Poland.
Example1: Chromatic Abberation is very apparent in this medium focus achromatic f7 60mm Astral refractor. (Observe the red and blue fringes at either side of Jupiter's disc).
Example2: Chromatic Abberation almost nonexistent in this excellent long focus achromatic f15 60mm Prinz 550 refractor. (Twice the focal length, twice the focal ratio)
< You can click this illustration to enlarge if it helps see the chromatic abberation effect.
This applies to Newtonian Telescopes. It does not apply to Refractors, Maksutov-Cassegrain, or Schmidt-Cassegrain telescopes.
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.
Manufacturers of small telescopes don't bother with this final 'figuring' of the mirror. It's time consuming and needs special testing of the optics.
Left: See the fuzzy stars on the spherical image.
They leave it out because it's an expense they can avoid - Their telescopes, however, are sub-standard as a result and give awful image quality. They try to get around this fault by supplying long focal lengths (f9 - f12) because the difference between the spherical and parabolic mirror is smaller (But still significant!).
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 130mm Newtonian.
Ray Diagram: The parabolic mirror gives much sharper point images and 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!
NOTE: This is not different colours being reflected to different points - It is all light - The colours in the diagram are to show different light rays only.
Diffraction Limited Optics – A good thing or a Bad?
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. But a badly made lens or mirror won't show all the detail a lens or mirror of its size should.
So, the limit for seeing fine detail in an image is dependent on the accuracy of the telescope mirror or lens. A lens or mirror that is perfect, optically, is said to be 'Diffraction Limited'. Because the only thing that is limiting its abiltiy to show detail is optical physics. That is, it's as good as it can be, given the size of the optics.
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, the mirror MUST be parabolic to achieve diffraction limited images. A spherically 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).
It is also known as The Rayleigh Limit.
R = 4.56/D D in inches, R in arc-seconds
R = 11.6/D D in centimeters, R in arc-seconds
D is the diameter of the main lens (aperture)
R = Resolution: 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 whether you should be able to split the double double in Lyra 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 refractors, Maksutov-Cassegrain and Parabolic Newtonian 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 it isn't and you'll have inferior views.
The biggest obstacle to your viewing clarity, however, 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!
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!”
See for Yourself:
Right Pic. - 150mm at 100x Magnification but with a larger aperture does, (More detail 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.
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)
As with many aspects of amateur astronomy, there are swings and roundabouts in the choice of mounting. You need to take some time to consider which type of mounting will help you achieve your goal.
If you want to learn your way around the sky and be able to use any telescope or binocculars to locate objects at any time, you might opt to learn 'the manual way', with an equatorial mounting that you have to operate yourself and point in the right direction. Use your skill to find convenient guide stars and 'star hop' your way to the object you want to observe. There is a lot of fun in this and it is very rewarding.
Alternately, you may want to be sure that you're looking at the right object and forego the learning of the stellar signposts, in favour of a robot telescope that will point to the object you want to see off a list. For you, the 'GoTo' mount is a good option. Beware, though, you will take much longer to learn where astronomical things are!
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 long exposure astro-photography as the field rotates as you track an object smudging the detail.
However, short exposures of ten seconds or so can be stacked to produce excellent pictures with experience.
As you have seen. There are a lot of "howevers" and "alternativelys" in this section. You have to decide which way is best for you.
When amateur astronomers like myself say "BIG", we have a better understanding than telescope sellers who have never seen a telescope over 2"... (Even "power sellers" - Don't make the mistake of thinking that people who sell lots of things necessarily know much about the things they are selling!)
You may notice the obvious difference between the two telescopes I'm advocating. Their size!
The objects seen in the larger telescope are visible because of the larger light gathering capability and greater resolution of the larger optics.
For the sake of getting a telescope of entry level (130mm) rather that a tiny 76mm telescope, you can see all these extra things!
A similar set of differences are seen between a 60mm refractor and a 90mm refractor - The smaller isn't much better than a toy, whereas, the larger will satisfy for many years!
This is a basic overview: For full information, including: Barlow lenses, Exit Pupils, and
other considerations, please access my Complete Magnification Guide
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) as a planetary observer I would choose one which gave about 150x magnification. Not 200x or 300x or even the fantastic 525x magnification - Just 150x*.
Useful magnifications vary with the size of the telescope.
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.)
< Have a look at this telescope
Even 'huge' telescopes utilise 'reasonable and usable' magnifications.
Above: The 30" telescope at the AAC was used to view Jupiter at 200x.
(That's me when I wasn't grey! Approx 1983)
The objects we look at are of different sizes and sometimes we want to see the whole, and sometimes the detail. Sometimes, you just think that a smaller
or larger view would help see the detail of what you want to view. Also there are exit pupil considerations - See magnification
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.
Eg2. Focal length 1250mm / Eyepiece 8mm = 156x magnification.
I would recommend you read the complete Magnification Guide.
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!
Refractor of 80mm or Newtonian of 130mm - The magic sizes I recommend!
(You can therefore see: I haven't just plucked these sizes out of thin air :o)
So, that's about it for the nitty gritty of what makes a telescope suitable or not.
You can stop here if you wish, now you are armed with the information.
The following extra titbits can be considered 'further reading'.
I have included these interesting points for anyone who wants the fuller picture. Please read on!
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... The Object Glass was so poor that there were no markings on Jupiter and although I could see the rings of saturn, I never saw Titan with this telescope (An easy object in almost any instrument over 25mm diameter) With that telescope I learnt, very quickly, that with a small, cheap telescope, 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 CAN NOW GET YOURSELF A VERY GOOD TELESCOPE FOR A WEEKS WAGES OR LESS!
You're looking for a Refractor 80mm and larger... Or a Newtonian 150mm and larger...
out for fantastic bargains on the second-hand market.
Grab a bargain...
Left: This 100mm SkyWatcher 100ED-PRO Refractor was found in a 'Cashconverters' store and they sold it to me for £89.99 - WOW! (This telescope OTA is £720 new!)
The scope has ED optics (Almost no chromatic abberation), it has a 50mm finder (Brilliant) and comes with a very good quality 2" diagonal and focusser. All-in-all, this is a superb telescope and I am very pleased - You could be the happy owner of such a scope for peanuts - Read my Second-Hand buying guide.
BUT, Please DO NOT...
Be tempted to buy any telescope SMALLER than the sizes I recommend in this guide or you will not see the detail that you deserve to see for the money. If you have patience you can get the scope you want for the same price as one of these binnable objects! See my second hand telescopes guide!
Left: This tiny spherically figured telescope will not begin to satisfy even your most basic astronomical needs.
I get quite a few messages asking what else you should buy to get started in astronomy when you get your new telescope.
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 130mm)
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!
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!
< 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.
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 absolutely invaluable for seeing how things work and planning your observing sessions.
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 and 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.
Above: Bino-Bargains: My excellent Swift 10x50s are superb and were got second hand for £19
My I.R.Vision 8 x 40 wide angle view binoculars are not ideal for astronomy but were better than nothing for a tenner!
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.
It can be beneficial to get a 2x Barlow lens. 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. Another consideration, if you are looking for Deep Sky objects, the Barlow will also double the focal ratio - f5 (fine for Deep Sky) becomes f10 - Not too good for Deep Sky!
There are many cheap plastic Barlow lenses available (£7-£9), but I would recommend spending about twice as much and getting a metal, achromatic Barlow (£12-£15) - The quality
of the image is well worth the extra outlay!
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.
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 essential and 30mm or 50mm is much more desirable for 150mm 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!)
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!
Left: A Proper Finder scope - 6 x 30mm
This will show objects down to magnitude 9. You can line up better because of the magnification and cross-hairs.
If you would like more information on this sunject, I have a separate guide that deals with this subject in greater detail.
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 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!
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 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 - Get some experience with the simpler telescope types before overcomplicating it for yourself!
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.
My own Travel
Scope is a Helios 80mm f5 refractor on travel alt-az with slo-motion control, that I picked up for £22.00
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.
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'.
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 Newtonian layout reflecting types of travel scope at all costs! They are far too delicate for true travel scoping! Refractors and Maksutov optical layout scopes 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 65mm to 75mm 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!)
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 a little 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.
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 for cheapness and simplicity (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.
For the purists:
The term 'Dobsonian' has come to mean any telescope on the 'Dobson Style Mount'. This has become so prevalent that it is even in several astronomical dictionaries as the definition!
However, the true definition of a 'Dobsonian Telescope' is slightly different and is worth knowing.
Many manufacturers, and even experienced astronomers mistakently think that the term 'Dobsonian' refers to the type of mounting it is on. An Alt-Az of particular construction.
This is not the case. Having spoken to John Dobson personally on this subject, these are the facts.
When John was creating the telescope design that became known as 'The Dobsonian' there were a number of considerations that influenced the design (ALL of which have to be present for a telescope to be a TRUE Dobsonian).
John was not bothered about patenting his ideas, he just wanted to get as many people looking through big telescopes as possible - Consequntly, there is no rule about what you can call 'a Dobsonian'.
To that end:
1: He ground large mirrors (12" and larger) out of thin glass blanks, usually 25 - 35mm thick. These were extremely thin by contemporary standards - A 12" 'ordinary Newtonian' would typically have a 65-75mm thick mirror and a 16" would have maybe 85-95mm thick glass. John Dobson made telescopes of 20" and 24" aperture with 60mm thick glass.
2: He avoided the complicated and expensive mirror cell by laying the mirror on a backboard with a simple plywood cell of three triangles and rubber points with a 'bib' over the top, sometimes with a layer of bubblewrap to support the thin mirror. The weight of the mirror was taken by a strap underneath the circumference. Because of this the telescope could ONLY be used on an Alt-Az mounting to keep the sling supporting the mirror.
3:This was OK in this design, because keeping costs low precluded the equatorial mounting. An Alt-Az it was. John made the mounting from plywood and a large bolt for the verticle axis and teflon pads to minimise friction. The altitude bearings were made of tubing and rested on teflon pads in the mounting cutouts.
John was pleased to be able to make a workable 20" or 24" reflector for the same cost as a 6" commercially bought telescope.
There's a video by John himself: Here> https://www.youtube.com/watch?v=snz7JJlSZvw&t=3608s
Watch video from about 55mins, for the mirror support part.
The above facts are largely unknown and figured only in interviews with Mr. Dobson in the astronomy magazines of the seventies and early eighties. The majority of people, following the manufacturer's lead, believe that the type of mounting is all that denotes a Dobsonian Telescope. It is a matter of fact, that this misconception will continue to prevail, and we will have to accept that these Newtonian telescopes of classic design, supplied on a 'Dobson Style Alt-Az mounting', will be referred to as Dobsonian Telescopes! (It's convenient and much less of a mouthful! :o)
Recommended for the beginner if your interest is soley in Deep Sky. The easy use mounting and easy-peasy set-up is intuitive and natural. At low to medium magnifications these telescopes give great images and can be recommended for beginners.
Left: John Dobson at the HAW: A 14" Newtonian on the 'Dobsonian Mounting' can be seen behind
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 is difficult for the beginner. I would respectfully suggest that the Dobson / Dobsonian telescope should be avoided until you get some experience with the easier to use 'equatorial mounting'.
If you see a 'Dobsonian' telescope advertised make sure it's not just a Newtonian on a Dobson mounting, or worse, they're calling it a
Dobsonian because it's on an Alt-Az mounting of simple design! ... To be a true Dobsonian telescope it has to have the thin main mirror supported on the sling type support and it should be
Call me pedantic, but they're selling you an Alt-Az Newtonian and telling you it's something special... NO.
The whole point John was trying to get across wasn't 'ease of use', if that was the point they would be mounted on equatorials! They were designed to be telescopes of huge diameter built at home on a shoestring! Mass producing Dobsonians seems to be missing the point entirely.
Anything that isn't huge*, and relatively cheap to boot, isn't really a Dobsonian at all, but a Newtonian 'dressing down' to snare the unwary!
Don't pay megabux for a Dob! (*By huge I mean 12" 300mm and over.)
There are a number of companies now selling Catadioptric Newtonians. I would
suggest that these are to be avoided by the beginner. (Click the pic for more info).
They have optically extended focal lengths - 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 above (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 optically flat piece of glass at the tube aperture and are consequently 'sealed systems' (See picture) - They use a Barlow lens in the focuser to extend the primary focal length in a short tube.
Some have this optical lengthening barlow, but have the usual spider 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: Firstly: The tube is closed by the corrector plate and this eliminates tube currents, Secondly: A closed system also lessens the tarnishing of the mirror surfaces. 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 because of the secondary).
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.
Left: This Bresser has a code that doen't relate to the optical perameters, but they are detailed on the label.
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.
In the interests of checking the accuracy of my claims I bought myself a 70mm f10 Bresser Refractor (off eBay, naturally!). As you know by now this is smaller than my minimum recommended size by 10mm. I did extensive observations of the planets, stars and Messier objects 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 enough for a beginner to get a real feel for astronomical observation. Falling only slightly short on the detail on the planets that I was hoping for.
Plössl eyepieces: Planets showed some detail - About what I would expect,
but not as much as the 80mm.
If you can't afford anything in the 80mm range, then the Bresser 70mm f10 is just about adequate (And actually better than the awful Celestron 80mm!) - Don't pay over £80 for a second hand one! At least we know where we stand!
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, and if you don't, you need to learn a bit more about how to set up a telescope.
Seriously, these telescopes could have sustained serious damage being upside-down!
No answer? Move on, buddy!
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. If it's not specifically stated look for the focal length. The 130P has a focal length of 650mm.) The mounting, just as the scope itself, is well designed and constructed.