The optically superior but larger W20-60X 80 mm spotter features fully multicoated lenses for crisp image quality, an extendable sunshade to combat against glare and a rotating collar that allows ...

Either 80 or 90mm will work ... EBM_PAPST 3212JH4 12 V, Square, 92 mm, 38 mm, 164.8 CFM (there's a static pressure chart in the spec PDF) ...