One model, judged by its numbers
GSO Dobson 300/1500
Where galaxies start having structure and planetary nebulae start having colour. Also where an instrument starts needing a plan rather than a decision.
Family · 250–300 mm Dobsonian
What it shows, really
These circles are simulations, computed from the aperture, the magnification and the sky — indicative, not exact. A real night also depends on the turbulence, your eyes and your experience. Closer to the truth than the photo on the box; still not a promise.
Under a suburban sky (Bortle 6), through a common 25 mm eyepiece for wide targets and a 10 mm for planets. Every circle is the true field — nothing is enlarged.
The numbers
| Aperture | 300 mm |
|---|---|
| Focal ratio | 1500 mm · f/5.0 |
| Mount | Full-size Dobsonian rocker box |
| Typical weight | 33 kg |
| Eyepieces | 25 mm |
| Useful magnification | 50× to 600× at 300 mm |
| Resolution (Dawes) | 0.4″ — the tightest double star this aperture can split |
| Faintest star, suburban sky | around magnitude 13.7 |
| Observed price | €899 seen 2026-08-30 |
Should you buy it?
- Yes if what you mainly want is nebulae, clusters and galaxies, by eye, the moon and the planets: that is what this family does best.
- No if your priority is learn my way around the sky, taking it with me: other families do better for the same money.
- 33 kg: you need to be able to carry it outside, every night, unaided.
Computed from its family's per-goal scores and its own numbers — not a rating, not one evening's opinion.
Made for
Nebulae, clusters and galaxies, by eye · 5 out of 5
The reason people own these. Nothing else at the price shows as much.
The Moon and the planets · 4 out of 5
Superb when the seeing allows, which is less often than the aperture would like.
Not made for
Learn my way around the sky · 2 out of 5
Not the instrument to learn on. The field is narrow and the setup is a commitment.
Taking it with me · 1 out of 5
No.
The family it belongs to: 250–300 mm Dobsonian
What it does well
- Spiral structure in the brighter galaxies, from a dark site
- Enough light that a nebula filter finally has something to work with
- Still the cheapest route to this much aperture by a wide margin
What it costs you
- 40 kg in two or three pieces. It needs a car, a plan and a body that agrees
- A cooling-down period of half an hour or more before it performs
- Under a bright sky, most of this aperture is buying background glow
Worth knowing about this model
The plain 300 mm: a parabolic mirror, a Crayford focuser, a wooden rocker box, and nothing electronic. GSO makes the mirrors that several other brands sell under their own names. 1.5 m long and 19.5 kg of tube — it needs a car, a cupboard, and someone willing to carry it, every single night.
Prices are observed on the date shown, never live. Links marked paid link earn us a commission and cost you nothing extra.
Where to buy
- Astroshoppaid link€899 seen 2026-08-30ships DE, FR, EU
- Amazon.frships FR
- First Light Opticsships GB
- Optique Unterlindenships FR
- Pierro Astroships FR
- Teleskop-Expressships DE, EU
1 of these 6 links earn us a commission, marked above. Sorted by price, never by what pays. How this site is funded.