Hi Jeremy
When you purchased your W.O. Binoviewers there should have been a pair of 20mm Widefield eyepieces and an 1.6X Optical Corrector in the box. At least mine did and you need to use the OC to reach focus with most refractors. This arrangement increases the magnification of the eyepieces by 1.6X , so that the 20mm then acts like an 12.5mm focal length giving 33.6 X in the 72mm x 420mm Skywatcher and an 2 deg. FOV.
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