# FIELD OF VIEW?

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Hi,  Need help on this one.There is a formula but I cannot remember it. Which eyepiece offers the widest field of view. X36 at F10 or X40 at F6.3.

Eyepieces in question  Televue 32mm  X40  at F6.3  and Meade 4000 series 55mm  super plossil X36 at F10    regards Dave

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The f ratio isn't relevant.

The 32mm (50° field) at X40 gives an actual field of view of 1.25°

The 55mm (50° field) xt x36 gives an actual field of view of 1.38°

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I suspect what you are thinking of is:-  FoV = Eyepiece Field / Magnification

So a 50 degree eyepiece (like a plossl) at 40x (as above) is 50/40 = 1.25 degree. Some plossl's will clain 52 degrees but it is usually a lot easier to work with 50.

If you get say a BST which is 60 degree eyepiece then it is 60/40 = 1.5 degree.

They are termed TFoV and AFov, but I cannot recall which is which, so safer if I don't use them as there is every chance I will get it wrong.

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Very useful info I can now apply this to all my eyepieces                 Dave

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