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F2.8 with a 20 mm eyepiece gives 21x. F3.2 with a 20 mm eyepiece gives 24x.
The field with a 100 degree eyepiece at 21x will be roughly 4.76 degrees. The field with same eyepiece at 24x will be about 4.16. So you lose 0.6 degrees by staying at F3.2. Personally I think a 4 degree field is huge so I would leave it at F3.2. It will be a little easier to figure too.
Rod
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