In June I put up a post on the exit pupil ‘sweet spot.’ I really enjoyed the variety of views on the topic, and recognizing that there was no broad agreement on the topic, filed it under ‘unresolved’ in my mind.
The latest Sky and Telescope (September 2005) shed some further light on the topic, suggesting that Maksutov might have been onto something when he claimed that 2-3mm provides the best resolution for the human eye. According to S&T, the eye’s aberrations (including spherical and chromatic) overwhelm aperture gains with a pupil of 3-4mm. This makes sense from an evolutionary perspective: night time pupils don't need to have such high resolution as day time pupils for survival.
Does this mean long focal ratio eyepieces aren’t worth it? Of course not. And yes, subjective experience at the eyepiece is more important than theory. But, it does seem that the pupil ‘sweet spot’ is not mere bunk, and may have its feet in science.
-David
The latest Sky and Telescope (September 2005) shed some further light on the topic, suggesting that Maksutov might have been onto something when he claimed that 2-3mm provides the best resolution for the human eye. According to S&T, the eye’s aberrations (including spherical and chromatic) overwhelm aperture gains with a pupil of 3-4mm. This makes sense from an evolutionary perspective: night time pupils don't need to have such high resolution as day time pupils for survival.
Does this mean long focal ratio eyepieces aren’t worth it? Of course not. And yes, subjective experience at the eyepiece is more important than theory. But, it does seem that the pupil ‘sweet spot’ is not mere bunk, and may have its feet in science.
-David
