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Message: <blockquote data-quote="Binastro" data-source="post: 3569433" data-attributes="member: 111403">Re post 53.Hand held binoculars typically have 1% larger fields when I measure them compared to tripod mounted.The two tubes generally have fields with a difference of less than 1.5% when I have measured them. Often I cannot discern any difference.However, star images are often slightly better in one tube, maybe because one has been slightly skewed for collimation. In really good binoculars it is sometimes difficult to see any differences between the two tubes.P.S.I am not sure that the FOV accounts for all the aberrations at the field stop, in practice.If using very bright stars like Rigel, I think that the light can spill in from just outside the field stop.I.e. It is impossible to determine when the star is at the field stop, or just within or just outside. Maybe the light spills in from poor atmospheric Seeing or reflections. I don't know the reason, but determining if the star is at the field stop is almost impossible.P.P.S.It may be because the collector, the eye and entrance pupil is not a point source but 4mm or 5mm across that the field stop is seen from slightly different positions that I cannot determine when a bright star is at the field stop. The star reduces in brightness as one moves near and across the field stop, but may vanish beyond the theoretical field stop.It is late now.</blockquote>