Search the Community
Showing results for tags 'nominal er'.
Found 1 result
Eye relief (ER) is a recurrent topic here, not least by glass-wearers, many eyepieces do provide nominal ER, assuming the numbers are correct (not always the case), there're still other factors affecting the actual available ERs, such as recessed or concave eyelens etc, since ER is defined from eyelens center to eye ploint. There's an interesting aspect brought up in the other site, which might affecting the ER positively https://www.cloudynights.com/topic/561801-bargain-widefield-ep-performance-in-a-flatfield-scope/?p=7624593 Here's the illustration picture: The point is: when observer's eye pupil is larger than the exit pupil produced, he can actual move his eye further away from exit pupil position and still see the whole FOV. I've made a couple of graphs to see its effect, the first one assuming dark-adapted eye pupil of 5mm, and eyepieces have 3mm recessed eyelens, It shows that an ortho (42° AFOV) with 4mm nominal ER (red line) behaves like having 10mm ER, despite 3mm recessed eyelens, that's about the same ER with a plossl (52°AFOV) of 6mm nominal ER, in another words, 5mm ortho is about as comfortable as an 8mm plossl. Second graph is with not well-dark-adapted eye, i.e. 3mm eye pupil, everthing else the same, The same ortho has only 7.5mm available ER now, compare to 10mm when pupil was wider,and the plossl drops to 8mm. Whats' your experience?