As wizard, would it be possible to use your familiar's line of sight as your own for spells such as Mirage Arcane which has a range of sight? Would You be able to use a telescope or spyglass to use that spell?
A familiar’s line of sight counts as your own when you are seeing from its eyes, and this works for spells that require line of sight, so yes for a familiar.
Their is no telescopes in RAW, so I’ll talk about spyglass. A spyglass does not increase how far you can see by the book, instead it “magnifies objects to twice their size, like a magnifying glass. So for this portion, I’d have to say no, not by RAW.