Picture an old brass spyglass lying closed on a table. You pull it open and one tube slides out of the next until it is long. Then you put it to your eye, and a ship far out at sea is suddenly close and large. Both halves of that picture live in the word: the tubes sliding out of each other, and the far thing brought near.
The word is built on telescope, whose parts go back to Greek tele, meaning far, and skopos, from the verb for looking at something. So the name of the instrument already says far-looking, and the adjective inherits it.
這個字建立在 telescope 上。它的字根一邊來自古希臘文的 τῆλε（遠），另一邊來自 σκοπός 那一支，跟「看」有關。所以工具的名字本身就寫著「看遠」，形容詞只是把這個意思接了過來。
Wiktionary entry 'telescopic', etymology tree (packet etymology_text; source_ref kaikki:3f6f69a190036ae4:992250888:19829)
From the picture
一節一節抽出來
望遠鏡除了鏡片，還有一個很好記的身體：可以拉長、可以推短的鏡筒。後來只要東西是「一節套一節、拉開變長」，英文就借這個字來形容，即使那東西跟看東西完全無關。行李箱拉桿就是最好的例子。
adjective · B2
Made of parts that slide inside one another, so the whole thing can be pulled out to make it longer or pushed in to make it shorter.
可伸縮的（一節套一節）
adjective · B2
Making things that are far away look bigger and closer, the way a telescope does.
有望遠效果的（把遠處放大）
adjective · C1
Done by using a telescope, or having to do with work carried out with one.
用望遠鏡進行的
adjective · C2
Used about a star or other thing in the sky that is too faint to see with your eyes alone, so it can only be seen through a telescope.
肉眼看不到、只能用望遠鏡看到的（天體）