2" eyepieces for 10" f/4.8?

Today I went into a scope shop who specialize in meade to look at 2" widefield eyepieces for my daughters 10" scope.

Everything above 25mm had a dark spot in the centre field of view and the shop owner said that it was the central obstruction and was a function of the scopes short f ratio.

Are there any eyepieces that have a high focal length (30mm and above) that will not show the central obstruction on a fast 10" dob?

>>Are there any eyepieces that have a high focal length (30mm and above) that will not show the central obstruction on a fast 10" dob?

This is not a function of the eyepiece (other than its focal length). Rather it is caused by the fact that during the day your eye's pupil is probably only open to about 2mm. At night when your pupil is open one does not see the central obstruction.

Consider a 30mm Eyepiece in an F5 scope with a 25% Central obstruction. The exit pupil is 30mm/5= 6mm. There is also an exit pupil associated with the central obstruction which is equal to 25% of that 6 mm exit pupil or 1.5 mm.

If you eye is only open to 2mm, that 1.5mm hole is definitely there to see but at night, your eye will dialate and open to between 5 and 7 mm and that 1.5mm hole is invisable.

Jon

Eugene, The shop owner said that it would be visible at night, so it was not just a worry on my behalf. Unfortunately also, I know of no shop owners who are prepared to allow me to use them at night and return them if I am not satisfied. As well, unlike many on this forum, I cannot afford to spend hundreds of dollars on something that may or may not work properly.

Thank you all for your replies. They have been most helpful

David