Published May 10, 2025 - updated regularly
Choosing your first telescope: ultra-complete beginner's guide 2025
Becoming an amateur astronomer means opening a window on the Universe: lunar craters, the phases of Venus, the rings of Saturn, distant galaxies... all accessible from your garden or balcony. Astronomy also offers educational benefits (physics, mathematics, history of science), a positive impact on mental health (connection to nature, stress reduction) and a social aspect (observation evenings with the family or a local club).
A telescope collects the light using a objective (lens or main mirror), focuses it and enlarges it using a ocular.
To find out the effective magnification of your telescope, divide the focal length of your instrument by the focal length of your eyepiece. Example: telescope focal length 1200mm and eyepiece focal length 10mm, so magnification = 1200/10 = 120x.
Visit two optical principles are :
Understanding these basics helps you choose the right instrument for your objectives: visual observation, astrophotography, nomadism, etc.
Article that goes into much more detail about these concepts: https://deep-space-astronomy.ch/choisir-son-telescope-les-bases-en-optique/
The larger the diameter, the more light the telescope can capture, showing fainter objects and better detailing planets.
Visit focus report (F/D) is calculated by dividing the focal length (F) through the opening (D). It influences the photographic field, brightness and object size:
Case in point: a Newton 150/750 has a focal length of 750 mm and a ratio F/5. With a 30 mm eyepiece (68° field of view), the real field of view is 2.7°, perfect for framing the Orion nebula (M42); in return, a coma corrector is desirable for photography.
Visit magnitude is a measure of the brightness of a celestial objectlike a star, a planet or a galaxy, seen from Earth.
The the brightness of an object as seen from Earth.
Two simple formulas help to estimate the magnitude that an instrument will be able to observe:
116 /Diameter (in mm) seconds of arc. A 200 mm solves ~.0,58″sufficient to separate Epsilon Lyrae.2 + 5 × log(Diameter in cm). A tube 150 mm (~15 cm) reaches mag ≈ 13,2 under Bortle 2 sky, revealing the galaxy NGC 891.These values deteriorate with turbulence (seeing) and light pollution. For example, under a Bortle 7 city sky, the same 150 mm will cap at mag ≈ 11 - enough for globular cluster M3 but not for galaxy IC 342.
Then all you have to do is find the magnitude of your object of interest and see if your telescope can observe it. The challenge is to observe an object as close as possible to your telescope's magnitude limit!
These are interesting data and formulas for geeks, but not necessary for enjoying the sky!
Visit surface accuracy is measured in fractions of a wavelength (λ); λ/4 is the minimum for visual use, λ/8 is premium. The Strehl ratio (from 0 to 1) synthesizes aberrations; a mirror with Strehl 0.94 restores 94 % of light in the Airy disk (which is good)
| Specification | Quality |
|---|---|
| λ/4 - Strehl 0.80 | Standard |
| λ/8 - Strehl 0,90+ - The | Top of the range |
| λ/10 - Strehl 0.95+ - The | Premium |
Visit coatings amplify reflectivity: a standard aluminized mirror reflects ~89 %; a treatment Hilux 97 % or Enhanced Alu 96 % increases brightness by almost half a magnitude, useful for photography. On the lens side, FMC multi-coating reduces glare and boosts contrast.
| Type | Subfamily | Benefits | Disadvantages |
|---|---|---|---|
| Astronomical telescopes | Achromatic (cheap but chromatic) Apochromatic (more expensive but chromatism-free) | High contrast (no central obstruction) Low maintenance, Ideal for beginners on a budget or for astrophotography. | High cost/mm (especially APO), chromatism if achro |
| Telescopes | Typically Newtons | Excellent price/diameter ratio, no chromatism, ideal for deep-sky viewing and observation | You need to learn how to adjust it (my training is offered with every purchase from DSA!). More cumbersome tube for larger focal lengths |
| Catadioptric | Maksutov, Schmidt-Cassegrain | Compact size, multi-purpose visual/photographic, tube closure limits fogging | Higher price than Newton, longer warm-up time |
Tip: if you're in good shape, a 200mm dobson will be ideal for observing (and ideally larger if your budget allows).
| Category | Function | Recommendation for beginners |
|---|---|---|
| Eyepieces | Vary the magnification of your telescope | Eyepieces Explore Scientific offer exceptional value for money. Focal lengths between 10 and 15 are great, and a 25mm and you're good to go. |
| Barlow | Double/triple magnification | Barlow 2× is ideal. Doubles your range of magnifications. |
| Lunar & planetary filter | Reduces glare, enhances detail | Neutral filter ND-0.9, yellow filter n°12 for Mars |
| Red dot researcher / Telrad | Fast scoring | A Telrad is very intuitive |
| Collimation | Adjust mirrors | 1.25″ eyecup or laser |
| Deep sky filter | Highlighting nebulae and galaxies | A UHC filter and an OIII filter enable detailed exploration of objects. |
All these accessories are available on the site!
| range | Budget CHF | Example | Ideal use |
|---|---|---|---|
| Getting started on a budget | CHF 229 | 80 mm Celestron scope. Good quality, sturdy tripod (this is not the case with cheaper, totally low-end scopes). https://deep-space-astronomy.ch/produit/lunette-celestron-starsense-explorer-lt80-az/ | Lunar and planetary observation, and under good skies the main deep-sky objects are accessible. |
| Start with the desire to immerse yourself in a few settings (it's still very simple). | 319 CHF | Dobson 150mm tabletop! Transportable, very high quality, and 150mm is starting to look like a nice diameter. https://deep-space-astronomy.ch/produit/dobson-bresser-messier-6-152mm/ | Moon, planets, deep sky objects with no problem (M31, M42, M31, M57, M27 etc.) |
| A no-nonsense way to get started with an instrument ideal for planetary applications | 559 CHF | The Maksutov is great for observing planets at high magnification. It's compact, high-contrast and really great quality. For those on a larger budget, a 127mm will provide even more detail. Mak 100mm: https://deep-space-astronomy.ch/produit/telescope-bresser-maksutov-cassegrain-100-1400-sur-monture-a-choix/ | |
| Serious and motivated amateur astronomer | 499 | 200mm Dobson. Now we start talking amateur astronomy. Hundreds of deep-sky objects open up. It's an excellent telescope! https://deep-space-astronomy.ch/produit/dobson-bresser-messier-8-200mm/ | Moon, planets, deep sky objects with no problem (the entire Messier catalog and much more) |
| Serious amateur astronomer ++ who wants to move under the best skies | 799 | 254mm Dobson with locksmith structure (dismountable and transportable). This is serious business. This is excellent equipment that will be with you for years to come. https://deep-space-astronomy.ch/produit/dobson-254-mm-10-f-5-ultra-light-gen-2/ | Moon, planets, deep sky objects, no problem, with almost no limits. An excellent long-term investment! |
Contact me to find out more!
You'll often hear about the Bortle scale. It's an approximate way of describing the quality of the sky.
| Bortle | Sky quality | Magnitude limit (naked eye) |
|---|---|---|
| 1 | Exceptional skies | >7,6 |
| 3 | Rural suburbs | 6,2 |
| 5 | Medium-sized suburb | 5,5 |
| 7 | Urban fringe | 4,5 |
| 9 | Downtown | <4,0 |
Move away to at least a Bortle 4 sky to reveal the Orion nebula and globular clusters.
Visit seeing measures air stability (good score = sharp planetary details). The transparency indicates clarity and absence of haze; crucial for deep sky. Consult platforms such as MeteoBlue Astronomy Seeing and Clear Outside before leaving.
What maximum magnification can I expect?
The rule of thumb is 2× diameter in mm. On a 200 mm, aim for 400× for excellent atmospheric stability. In standard conditions, the rule is 1.5 x diameter. For a 200mm lens, aim for 300x maximum.
How do you get to 300x?
You take the focal length of your telescope. Let's say it's 1200 mm (it's often marked on it).
Then you choose a ocular. If you take a 4 mm eyepieceit's been 1200 ÷ 4 = 300. So you're getting fatter 300 times.
But here's my tip:
Buy a 8 mm eyepiece and a Barlow x2 (this doubles the magnification).
That way, you have two options:
So you 150x and 300x with a single eyepiece + a Barlow. Simple, inexpensive, effective.
Are GoTo useful for beginners?
Yes for polluted skies where few landmark stars are visible, but learn manual pointing too. It's a philosophy, but I personally like both.
Should I choose a 1.25″ or 2″ eyepiece?
For starters? 1.25″ will do just fine!
What's the difference between achromatic and apochromatic?
APO combines several special glasses to eliminate almost all chromatism; ideal for photography and high-magnification viewing. But frankly, you don't take an apo telescope to observe - it's far too expensive for the diameter. So, for beginners = achromatic telescope, for high-resolution wide-field photography = apochromatic telescope.
Can you see galaxies with a beginner's telescope?
Yes, M31 is visible in an 80 mm lens under dark skies. The larger the diameter, the greater the detail.
How do I clean a lens without damaging it?
Souflette first, then micro-fiber cloth + optical solution, dabbing gently.
Can an 8-year-old use a 200 mm Dobson?
Yes, with supervision, but bring a stepladder and a red dot finder.
Barlow: Divergent lens that multiplies magnification.
Collimation: Optical alignment of mirrors/lenses.
Magnitude: Logarithmic scale of star brightness (smaller = brighter).
Seeing:Turbulent stability of the atmosphere.
Stacks: Stack images to improve signal-to-noise ratio.
Choosing your first telescope is step number 1 in a passion that can last a lifetime. Thanks to this guide, you now know :
Visitez la boutique pour commander votre télescope et appelez-nous en cas de doutes, on est là pour ça et on saura faire votre bonheur 🙂
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