Re: How close to 2mm?

I think the reasoning is based on the idea that 2mm is the MAXIMUM exit pupil at which one expects the macula to be able to resolve the smallest details present in the image. BTW, I don't know where this information comes from, but it is in the lore of amateur astronomy. Smaller exit pupils make it easier to see fine details by spreading them over more retina, but this comes at the cost of brightness per unit area on the retina, so 2mm is supposedly all the detail at maximum brightness. In practice, though, I think higher magnification helps immensely for resolving bright detail, and with DSOs that require averted vision a larger exit pupil may be preferred. Interestingly enough, I actually found ~2mm to be in a sort of no-man's land in my 10" f/5 where I was always wanting either more magnification or less. But go ahead and buy the eyepiece. Life is short. :-) -- Mike