FIELD-OF-VIEW AND EQUIVALENT VIEWING POWER OF NEAR-VISION TELESCOPES

There are often substantial differences in linear field of view (FOV) and equivalent viewing power (EVP) when a distance telescope is either fitted with an objective lens cap or adjusted in length to focus for near vision. In addition, larger differences in linear FOV are found f or Galilean than for Keplerian telescopes of similar magnification and EVP. Simple formulas are presented here that make use of EVP as a fac tor for calculating the linear FOV ratio between the two methods of co nverting distance Galilean and Keplerian telescopes for near vision. E xamples are provided to illustrate the clinical application of these f ormulas. The information presented here may be helpful when making rec ommendations concerning the most appropriate method of converting a te lescope for near vision.