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It is a waste of time because the adapter would heavily vignette the field of the 2" eyepiece.
There are some 1.25" eyepieces with field stops a bit wider than 27mm--the Baader Hyperion 24 (28.5mm), the Baader Eudiascopic 35mm (29mm), and a few others (most discontinued), but the difference is not large.
The formula you seek is:
TF=(FS/TFL)x57.296
TF=True Field in degrees
FS=Field stop in the eyepiece
TFL=Telescope Focal Length
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