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va1erian,
The maximum true field of view possible in an eyepiece is set by the inside diameter of the barrel. For polls this will be achieved with a ~25-30mm eyepiece. The effect of using a longer focal length eyepiece (in this case 40mm) is that the true field of view remains limited by the barrel, and its apparent (angular) field of view is limited to ~ 30 degrees. A bit like looking into a toilet roll.
Personally I'd suggest for your scope you should look for eyepieces in the range 7 ~ 28mm in 1.25 " barrels, and there are plenty of bargains to be had under $50. If you can find one secondhand, a set of Edmund RKE's (8, 12, 15, 21 and 28mm) would be perfect for your scope.
If your scope can accommodate a 2" eyepiece barrel, then you can usefully use something like a 40-50mm, but these don't come cheaply.
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