When dynamic FOV is turned on, zooming in with a spyglass doesn't actually zoom in. To be completely honest however, I really don't know if this is intentional or not, but just figured that I would inform you if it wasn't already known.
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We're tracking this issue in MC-228715, so this ticket is being resolved and linked as a duplicate.
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"Dynamic FOV" isn't part of the options menu; there's only "FOV Effects", which does not impact the Spyglass' function in any way.
Does MC-228715, caused by OptiFine, describe your issue?