70/700 refractor, alt-az: what you actually see
The 100–150 € first telescope. Fine on the Moon and the planets; the wobbly tripod, not the glass, is what people give up on.
With the eyepieces in the box
A 70 mm aperture through its 25 mm · 10 mm eyepieces, under a suburban sky. Every circle is the true field; nothing is enlarged.
Recognisable
Recognisable
Photo credits
These thumbnails are built from real photographs, scaled and darkened by the same arithmetic as the large view.
Where to buy one
The 9 mm eyepiece gives 78× on 70 mm, an exit pupil of 0.9 mm; with the 2× Barlow in the box it reaches 156×, an exit pupil of 0.45 mm, past the 140× that 70 mm can use. 5 kg in all, tripod included.
Where to buy
Also search at First Light Optics · Optique Unterlinden · Pierro Astro · Teleskop-Express (searches; neither price nor stock checked)
1 of these 5 links earn us a commission, marked above. Sorted by price, never by what pays. How this site is funded.
Listed because it is what most high-street searches return. The optics are fine for the Moon; the tripod is light enough that the image shakes for several seconds after each touch. With the included 10 mm eyepiece it gives 90× on 70 mm, an exit pupil of 0.8 mm: Saturn’s rings and Jupiter’s belts, once the image settles.
Where to buy
Also search at First Light Optics · Optique Unterlinden · Pierro Astro · Teleskop-Express (searches; neither price nor stock checked)
1 of these 5 links earn us a commission, marked above. Sorted by price, never by what pays. How this site is funded.
Try it yourself
- Here the sky is the limit, not the telescope
28× · 70 mm f/10.0 · exit pupil 2.5 mm · field 1.79°
Target
What this setup reaches — 11 of 14Instrument
Start from a telescope people buy
Worth knowing before you buy one
The 100–150 € first telescope. Fine on the Moon and the planets; the wobbly tripod, not the glass, is what people give up on.
Stars to magnitude 10.5 under this sky · resolves 1.66″
why?
How much light and how much detail. The only number that sets a ceiling on what is possible.
Focal length 700 mm: sets each eyepiece's power, not the light.
why?
Focal length 700 mm. Changes the magnification an eyepiece gives, not how much light arrives.
How much aperture for The Orion Nebula?
why?
Observers' experience, not physics — thresholds adjusted for Bortle 6. Tap a rung to try it.
Eyepiece
28× · 70 mm · 2.5 mm28× — the 2–3 mm pupil sweet spot for the deep sky.
why?
28× — a shorter eyepiece magnifies more, and dims everything as it does. The slider runs the way the boxes are numbered: left is short and powerful.
28× on 70 mm at f/10.0 — 2.5 mm exit pupil
Plössl — the standard bundled eyepiece
Sky
6 — bright suburban, Milky Way only overhead if at all
why?
Under a Bortle 4 sky this same 70 mm would show recognisable — it looks like what it is. To match that from where you are, you would need about 79 mm of aperture. A drive is cheaper.
The air (2.5″) limits detail before the optics (1.66″).
why?
How steady the air is, in arcseconds. Tonight the atmosphere (2.5″) is the detail limit, not the optics (1.66″) — a bigger telescope would not show more.
The cheapest that does the job
The smallest instrument that makes it recognisable: 79 mm · The Orion Nebula, Bortle 6
Cheapest in the catalogue at that aperture: Sky-Watcher Heritage 130P FlexTube (130/650) — €197 · seen 7 Oct 2026 at Astroshop · Chosen by price alone.
The Orion Nebula, honestly
Detectable — you can tell something is there
A grey-green fan of light wrapped around four close stars. One of the few deep-sky objects that survive a city sky, and the only nebula most people ever see colour in.
The dot fills as the object gets easier: none, detectable, recognisable, detailed. An observing heuristic.
The four stars at the centre are the Trapezium, at least 8.7 arcseconds apart: any small telescope splits them at 40× (in a 70 mm, an exit pupil of 1.8 mm). From 100 mm the wings and a mottled texture appear. Colour depends on the eye: many observers see only grey or a pale green; from 150 mm some see hints of red at the edges, rust in 250 mm.
Winter evenings in the northern hemisphere; summer in the southern.
The sky is the limit here, not the telescope
Under a Bortle 4 sky this same 70 mm would show recognisable — it looks like what it is. To match that from where you are, you would need about 79 mm of aperture. A drive is cheaper.
The numbers
28× on 70 mm at f/10.0 — 2.5 mm exit pupil
True field 1.79° = 107′ · focal length 700 mm
Brightness 1.6× of a 2 mm exit pupil · detail limit 2.50″
A 2.5 mm exit pupil — comfortable. All 70 mm of aperture is reaching your eye.
Which targets are reachable is an observing heuristic — somebody else’s eyes, somebody else’s night — and so is the 2.5″ of atmospheric seeing assumed above. The magnification, exit pupil, field of view and surface brightness are arithmetic and are exact.
Nebulae and galaxies are grey because they are grey to the eye: almost no colour response at these light levels — the photographs you have seen are long exposures. The Moon and the planets are bright enough to keep theirs.
Built from a photograph — NASA, ESA, M. Robberto (heic0601a), CC BY 4.0 — used only as input: scaled to the true field, then darkened, blurred and desaturated by the arithmetic. Nothing here is brighter, sharper or more colourful than the exit pupil allows.
The Orion Nebula: NASA, ESA, M. Robberto (heic0601a), CC BY 4.0