I know it’s optical, but what for?
Telescope eyepiece.
Made by these guys.
Oh, thanks. I knew it might be something like that, but the amazon page wasn’t very helpful.
Yup, telescope eyepiece. The eyepiece is standardized so it works on any telescope. (Well, actually there is more than one standard, but not too many). Changing the eyepiece changes the magnification, and replacing an eyepiece with a better quality one can give you a sharper image, wider field of view and/or increased “eye relief” (how close your eye needs to be to get the full field of view). High end amateur telescopes don’t even come with eyepieces because most users already have a set of eyepieces they like. A high end eyepiece can cost over $600 and weigh over a pound.
What, you mean apart from providing a link to this Celestron page, and having the legend:
**Photography > Binoculars, Telescopes & Scopes > Telescopes > Accessories **
at the bottom of the page?
Well I didn’t mean it was impossible to find out what it is. I just meant they didn’t make it obvious.
I made the thread to make a statement about ambiguity (and because I generally wondered what it was)
And I am stupid - I didn’t think to click on the link.
‘generally’? I meant to say ‘genuinely’.