Good morning,

The knob on the side of the body is attached to a sliding prism that is designed to be move into or out of the light path to direct the light to the triocular port. Unscrewing it will not solve the problem as it is only a device to push and pull the prism. More than likely the prism is damaged. Your best solution is to contact the seller and discuss any warranty protection.

Good luck with your efforts,

g2b2

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