Dobsonian

Every time I load the 8-inch Dob into the back of the car and drive the hour up to Troodos, it arrives out of collimation. Not badly (the mirror doesn’t slide across the cell), but enough that a defocused star at 200× shows the diffraction rings piled up on one side instead of sitting concentric. On an f/6 tube that costs me a sliver of sharpness on Saturn; on a faster f/4 it would gut the whole view. Before I look at anything, I spend ninety seconds putting the optics back into line. This is that routine: what collimation actually is, the two tools worth carrying, the one trick that makes a cheap laser trustworthy, and the star test that tells you when you’re done. ...

The two most useful eyepieces you can own probably aren’t the two that came in the box, and choosing them takes two numbers, not brand loyalty. Your telescope most likely arrived with a 25mm and a 10mm eyepiece. This piece is about what those millimetres actually do, why the 10mm is so uncomfortable to look through, and which two eyepieces to add first so you cover the sky from wide star fields to the cloud belts on Jupiter. No “best eyepiece” ranking. Just the arithmetic, worked on the scopes beginners actually buy. ...

If you have €120–€180 and you’ve never owned an astronomy instrument, buy a pair of 10×50 binoculars. Don’t buy a telescope. I’ve watched too many friends spend €200 on a wobbly 70mm department-store refractor, see Saturn as a tiny pixel-blur once, and shelve the thing for good. There’s exactly one case where that advice flips, and I’ll get to it. But the default answer, for the person walking into this hobby with no gear and no specific target in mind, is binoculars. ...