Focallength

2 clues
Telescope measure
It's variable with a zoom lens [Ginsberg]
Similar answers:
Anylengths
Armslength
Atarmslength
Atlength
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Bifocallens
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Calflength
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Focallength
Focally
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Focalpoint
Fulllength
Fulllengthmovie
Goestoanylength
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