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I think this technique does work, but only on telescopes such as Schmidt-Cassegrains, (SCTs) where there is an enormous range of focus travel.
SCT’s focus by causing the moveable main mirror to slide backwards and forwards on a shaft inside the telescope tube.
Newtonians have a fixed main mirror and a more limited range of focus, restricted to the length of the focus tube, from fully retracted (in) to fully extended (out).
Refractors tend to have a slightly larger range of focus travel as the focus tube is usually longer than Newtonians, although not as long a range as SCT’s.
Cheers
Dennis
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