White phosphor is a bad idea because it is less efficient (short wavelength photons are more energetic, so for a given electron energy, fewer photons will be produced) while it creates chromatic aberration in the eye lens. The fovea has poor blue resolution also.
Numerous issues depending on type (monocular, biocular, binocular). Binoculars must be coaligned, while diopter and interpupillary distance must be correctly set for your eyes.