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Hi Danial,
A 40mm focal length eyepiece with a 2" barrell will work fine. It will give you an exit pupil of 6.67mm in your 8"/f6 dob which is ideal for your lowest power eyepiece under your rural skies.
A 40mm eyepiece with a 1.25" barrel IMO is completely useless and manufacturers should not even be allowed to make them. Because of the restriction on the field stop aperture, they have a maximum Apparent Field of View (AFOV) limited to about 42 degrees. By comparison, a 40mm eyepiece having a 2" barrel can have an AFOV up to 70 degrees.
Cheers
John B
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