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Originally Posted by gaa_ian
Well we finally have our new 18" dob up here in Gove.
We stuck with a a 40mm Konig eyepice for most of the evening as this gave the easiest viewing.
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Gai-Ian
Congrats on first light with your new scope.
Do keep in mind issues with exit pupil on fast scopes. A 40mm EP has an 8.88mm exit pupil with an F4.5 and at best a young eye will have 7mm so accounting for the eye pupil stopping down the aperture at the eyepiece , you would only be seeing 14" of the mirror aperture . The situation with older eyes would be worse of course. A 28mm focal length if your eye opens to 7mm is the longest FL eypeice you can use with a F4.5 and without effectively throwing light away. People are sometimes impressed at how good the star images look at the edge of these big low power eyepeices. This is becasue with for exapmple the 40mm EP, your pupil is stopping the scope down to F7 or so which allows the eyepiece to works much better at the edge definition: less astigmatism and apparent coma.
Mark