Made a crucial adjustment to optical device (6,6)

I believe the answer is:

camera lucida

I'm a little stuck... Click here to teach me more about this clue!

'optical device' is the definition.
'camera lucida' can be an answer for 'device' (camera lucida is a kind of device). I'm unsure of the 'optical' bit.

'made a crucial adjustment' is the wordplay.
'adjustment' is an anagram indicator.
'made'+'a'+'crucial'='madeacrucial'
'madeacrucial' is an anagram of 'CAMERA LUCIDA'.

'to' is the link.

Can you help me to learn more?

I've seen this clue in The Hindu.

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