Telescope part (4)

I think it could be either:

Which length description are you looking for?:

3,4 4*

'telescope part' is the definition.
(I've seen this in another clue)

This is the entire clue.

(Other definitions for lens that I've seen before include "Focusing glass" , "Focussing device" , "Piece of glass, usually curved" , "Device to converge or diverge light" , "Bender of beams" .)

I've seen this clue in The Star Tribune, the Universal and the LA Times.

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