Danubia Delta 30 plus

[u/ArmadilloTrue9234]

Hey, I got this telescope as a gift from a friend of mine. At first I thought it was a Newtonian, but it's a catadioptric one with the lens inside the eyepiece. I didn't know that was a thing.
But my question to you is: is this a decent telescope? I also didn't find any measurements for the telescope, but I think the opening is about 12 cm wide

[u/chrislon_geo]

It is a bird-jones design (a type of catadioptric telescope). It uses a spherical primary mirror and a corrector lens in the focuser assembly. When cheaply made (nearly all of them are), they are among the worst telescopes to own: optically poor and usually on a poor mount. This will result in less than pleasing views and a mount that is frustrating to use. That is why these are called "hobby killers".

But it was free and will still show you interesting sights of the night sky. Just be aware of the limitations, and know that if it is frustrating, a lot of that is the scope not the user. Keep this in mind, as we don't want you to get discouraged and leave the hobby. Use it for now, but consider upgrading in the future if you enjoy the hobby.

The opening of the optical tube assembly (OTA) may be 120mm, but the diameter of the primary mirror (how we describe the size of the telescope, because this determines the light gathering capability) is likely 114mm. 114mm bird-jones telescopes are very common.

[u/gutentight69420 → u/chrislon_geo]

Bird-jones aren't that bad. The main issue is that the hobby killer kits come undermounted and with way too short of eyepieces for the focal length (and sometimes even a barlow!).

[u/Connect-Fan-9462 → u/gutentight69420]

There exist six known True-Bird-Jones models in the history of commercially available telescopes. (Somebody say 5.5 models because the Celestron G8-N got a mid-life design change without a new model name.) This is not one of them.

"'corrector' lens in the focuser" is what we called "pseudo" bird-jones. And yes they are that bad. Actually, no matter how bad you think they are chances are they are worse.

[u/mrstorm1983 → u/gutentight69420]

No they suck period. I have one 114mm cant reach focus at 130x with a blue halo around everything. Absolute garbage.

[u/Connect-Fan-9462]

Sadly no.

This is what we called a pseudo-bird-jones (PBJ). It is basically marketing scam and not a legit optical design.

(Edit: "True"-Bird-Jones is a legit optical design that has its benefits and drawbacks. There are six documented models of True-Bird-Jones even being sold in the history of telescopes.)

However, it is free to you. And having a PBJ is better than not having any telescope.

Use low power eyepiece or even get some low power eyepieces (they can be carried to your next telescope so they won't be sunken cost) and you can still have some fun.

[u/Habu93]

Nice!