Assembles lens in complete innocence (13)

I believe the answer is:

blamelessness

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'innocence' is the definition.
(blamelessness is a kind of innocence)

'assembles lens in complete' is the wordplay.
'assembles lens' can be anagrammed to 'BLAMELESSNESS'.
Though, I'm unsure how this is indicated.

Can you help me to learn more?

(Another definition for blamelessness that I've seen is " innocence".)

I've seen this clue in The Irish Independent.

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