The rule of thumb goes that you shouldn't use eyepieces that exceed a 7mm exit pupil, especially in telescopes with central obstructions. But rules are there to be broken, and being a young, rebellious chap (with quite large pupils), I decided to try out the 40mm in my f/5 and f/4.5 reflectors, giving 8-9mm exit pupils. I did not notice any central darkening and in fact got very pleasant views. I have to say it is one of the sharpest widefield 2" eyepieces I have tried, and performs very well even at these focal ratios.
Eye relief is pretty generous, but not too long as to cause kidney beaning - it is very comfortable to view through. Build quality is not up to the high-end standard, but is perfectly adequate. I very much appreciate the tapering barrel as it provides security without the likelihood of getting caught on compression rings. It is also small and light for a 2" eyepiece.
One curiosity I noted about the 40mm is the inability to fully accept 2" filters. They screw in about half a turn before jamming.
In summary, a fantastic sharp eyepiece with a very reasonable price tag.
