A tube that can slide or be drawn out and retracted, commonly used in microscopes, telescopes, and other optical instruments to adjust focus or length.
Compound of 'draw' and 'tube' (Latin tubus). Scientific instrument terminology developed as optical technology advanced in the 17th-18th centuries.
Drawtubes were the first adjustable zoom mechanism—before modern screw-focused microscopes, scientists would literally slide tubes in and out to find the perfect focus, a hands-on way of discovering the invisible world.
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