Why do chest bucky stand require long focal lengths

Why does the bucky stand require a long focal length? What is the “convergence distance” of the vertical bucky stand? The convergence distance of the vertical bucky stand refers to the distance between the beamer mirror and the frame box. The explanation is not necessarily accurate, if you have other questions, you can call our customer service for consultation. Briefly introduce the photos of our company’s wall-mounted bucky stands:

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