The feeling of excitement from purchasing your first telescope can quickly turn to frustration and disappointment if you lack the correct accessories. A telescope on its own is a powerful instrument, but is limited without the necessary extras.
This buyer’s guide will help you understand which accessories are most essential; their function and what to look for before purchasing. Each accessory also has a top pick purchase to make the buying the best telescope accessories simpler.
Finderscope
Imagine trying to find a pin-point of light in a vast ocean with only a tiny window to see through! Thankfully, a finderscope overcomes that challenge for you.
It looks like its own version of a mini telescope, and is mounted onto your actual telescope. Finderscopes have very low magnifying power so that the field of view is quite large. This makes it easy to locate objects within the finderscope. You will be able to observe an object through your telescope once it is centred in the finderscope’s crosshairs.
The finderscope naturally has to be aligned to the telescope for this to work. This is best done during the day, pointed at a large item close by, such as a streetlamp or chimney. Get the object in the finderscope’s crosshairs, then check that the telescope itself is focused accurately on the object. You get the finderscope aligned by adjusting its screws.
There are different types of finderscopes. The simplest design is a straight find scope. They have low magnification and very wide field of view, but the image is usually inverted. Right angle correct image finderscopes are similar, but the image is the correct way up. The finderscope is also more comfortable to use because of the eyepiece being on top.
Finderscopes also have various centres, from crosshairs to LED red dot finders. Some finderscopes use lasers which are highly accurate but must be used with caution and care.
Top Pick Finderscope – Orion 7211 6×30 Right Angle Correct Image Finder
The Orion right angle finderscope is comfortable and convenient to use – its design means no crouching over or having to strain to use the device. The finderscope has fully coated achromatic optics with a built in prism that provides sharp image correction (your view won’t be inverted.)
Eyepieces
Telescopes often come with budget eyepieces which make the quality of the primary optics completely null and void. A quality set of eyepieces is a must for yielding sharp, clear images. Consider the magnifying power and field of view of any eyepiece you purchase.
- Magnification
Find your telescopes focal length – a number written in millimetres which shows how far light must travel from the main optic to the point where light is focused. The eyepiece has its own focal length too, also written in millimetres.
Now, to calculate the magnification power of an eyepiece, simply divide your telescope’s focal length by that of the eyepiece’s focal length. If your telescope’s focal length is 700 mm and you use an eyepiece of 25mm, the magnification would be 700/25 = 28 x magnifying power (or simply expressed as 28 power)
High magnification is not everything though: excess magnification causes you to lose contrast and detail.
- Field of View
An eyepiece’s apparent field of view, indicated on the eyepiece and measured in angles, expresses how much of the sky ‘fits’ inside the eyepiece. The field of view could be quite narrow (25 – 30 degrees) to very wide (80 degrees or more). Magnification will affect the apparent field of view, resulting in what is called an actual or true field of view.
True field of view is calculated as such: the apparent field of view divided by magnification. Note that low magnification yields a larger field of view.
Top Pick Eyepieces Set – Orion 10mm, 17mm, 25mm Sirius Plössl Set
Excellent value for money from the reliable Plössl name, this three piece set guarantees sharp, clear images. Each piece has a 52 degree apparent field of view and is threaded for 1.25 inch filters. Compatible with all kinds of telescopes.
Barlow Lens
Want a quick and cost effective way of having more magnifying power? A Barlow lens does just that: placed into your telescope before positioning the eyepiece, the lens instantly doubles or triples the magnifying power of the eyepiece. The trade-off is a small loss of light and detail.
Be sure to consider your selection of eyepieces based on your Barlow lens so that you do not end up with duplicate magnifications. A 10mm eyepiece is redundant if you have a 20 mm and a 2x Barlow Lens.
Top Pick Barlow Lens: Astromania 1.25 inch 3x Short Focus Barlow Lens
Instantly increase the magnification of any eyepiece threefold. The lens maintains good sharpness, colour contrast and clarity. It is threaded for all 1.25 inch filters, and compatible with DSLR cameras for astrophotography.
Filters
Simply put, filters add dimension to the images of what you view. The Moon, planets, and deep sky objects take on a new life with filters.
They work by controlling the amount of light you see, and the type of light that reaches your eyes. Different types of filters are needed because the celestial objects all have unique makeups. A dark yellow filter can bring out detail on the Martian surface and polar ice caps; whereas a light pollution reduction (LPR) filter blocks forms of light pollution, reduces sky glow, increases contrast, and cuts harsh glare.
Filters of each kind are recommended for a full basic kit:
- Sun Filter
Choose a full aperture Sun filter which fits over the front opening/ main optic. These types of filters are non-negotiable for safely viewing the Sun, as they block 99.9% of all sunlight before it even reaches the telescope’s tube.
- Planetary colour Filters
These are ordered by number + colour, a collection which can become quite extensive. However, you may only need three or 4 basic colour filters to get started with. They are often called planetary filters because they enhance surface and atmospheric details of the Moon and planets.
- Narrowband Filters
Narrowband filters, or nebulae filters, are designed to help faint, deep sky objects like nebulae stand out. They increase the detail and contrast of these far away objects.
- Line Filters
Filters that are even more narrowband than nebulae filters. They are ideal for viewing certain kinds of nebulae.
Top Pick Filters Kit: Neewer Moon Filter, CPL Filter, 5 Color Filters Set
The kit comes with 1.25-inch filters compatible with all kinds of telescopes, and includes five colour filters, a CPL filter and an ND96 neutral density filter. The colour filters – 12 Yellow, 21 Orange, and 80A Blue – can be used for viewing the Moon, Mars, Jupiter, Saturn, Uranus and Neptune combined. The ND96 neutral density filter is great as a lunar filter, for splitting double stars, and cutting glare.
Star Charts
Star charts are vital to getting the full experience of backyard astronomy. It is good fun to learn your way across the stars – a mighty impressive skill to show off to your family and friends! A good old fashioned planisphere is simple to use and has all the information a beginner could need.
Consider a star chart app for a tool more modern and savvy. App stores have some excellent ones you can download for free. Using GPS, you simply point your phone at the sky (night or day) and the app will display the constellations and stars within that part of the sky.
Top Pick Star Chart App: Star Chart by Escapists Games Limited
The app has over 30 million users worldwide, helping amateurs learn their way across the sky. Point your phone heavenward and behold beautiful illustrations describing that exact region of the sky, both graphically and with interesting facts. The software is programmed for both hemispheres; including the 88 standard constellations and the entire Messier catalogue. Programmed for voice commands (“look at Orion”), it could not be easier to use.
Red Flashlight
A flashlight as an essential telescope accessory? Yes! Our eyes are very light sensitive. Our pupils become smaller in a lot of bright light to protect our eyes from being overwhelmed. The opposite is true in dark conditions. Our pupils become larger in dark environments so that we can take in as much light as possible to see in the dark: very important when stargazing.
Our eyes are dark adapted when they adjust to low light and become wider. Most wavelengths of visible light will overwhelm the eyes, causing you to lose dark adaption. But an amateur astronomer still needs to see what he or she is doing – using star charts, pouring coffee – and so a light that doesn’t compromise your night vision is required.
Red light is not harsh on the eye, making it perfect to use as an astronomy flashlight.
Top Pick Red Flashlight: Celestron 93522 Astro Vision Flashlight
An affordable device which is lightweight and compact, uses two red LEDS, and runs on a single 9 volt battery. The flashlight as the option to adjust the brightness according to what you need – a great added feature.
Conclusion
Your collection of telescope accessories will inevitably grow to include more equipment and software: a CCD camera to capture the heavens, a dew heater to protect your lens and always ensure clear images, or even just adding filters to your set. With everything you look to purchase, opt for reliable, quality items – they can be affordable – and maintain what you do have. These accessories can last for many years and be a true investment.