Hi cfraser,

A very warm welcome to CN and to joining us on this our special Celestron Nexstar Forum !

Your 8SE has a focal length of 2030mm. When you use your f/6.3 Reducer this has the effect of reducing that figure to 1279mm. (2030 X 0.63 =1278.9).

Your Hyperion Zoom has a range of focal lengths as follows : -- 24mm, 20mm 16mm 12mm and 8mm, so the magnification each of these focal lengths produce is gained by dividing the focal length of the 8SE by each focal length of this Hyperion Zoom eyepiece.

i.e.
Without your focal reducer:
2030/24 = Mag. X85
2030/20 = Mag. X102
2030/16 = Mag. X127
2030/12 = Mag. X169
2030/8 = Mag. X254

With your 6.3 focal reducer:
1279/24 = Mag. X53
1279/20 = Mag. X64
1279/16 = Mag. X80
1279/12 = Mag. X107
1279/8 = Mag. X160

The True Field of View, (TFOV), is determined by dividing the Apparent Field of View, (TFOV), of any eyepiece by the Magnification it produces with any given telescope. The Apparent Field of View is a property of the eyepiece resulting from its optical construction.

Thus for example, a Ploessl eyepiece has normally a nominal 50 degree AFOV. If then it's, for example, a 25mm, the magnification it produces in your unreduced focal length 8SE will be 2030/25 = X81.

To establish the TFOV therefore, for this 25mm EP when used on on your 8SE : divide its AFOV by the Magnification it produces: ( i.e. 50/81 = 0.62 degree or 37.2 arcminutes [60arcmins. = 1 degree: thus: 60 X 0.62 = 37.2arcmins).

On the other hand, with your focal reducer in place, the same EP would give you a TFOV of 50/(1279/25 = X51)= 0.98 degree or 59 arcmins.

Now to your Hyperion Zoom,. According to specification its AFOV ranges between 50 and 68 degrees. If you work on the basis that the 24mm and the 20mm are 68 degs. AFOV and the 16mm, 12mm and 8 mm are 50 degs. AFOV, then the TFOV for each eyepiece offered by the zoom would be as follows when using your 6.3 reducer :

24mm = AFOV. 68degs./X53 = TFOV. 1.3degs.
20mm = AFOV. 68degs./X64 = TFOV. 1.1degs.
16mm = AFOV. 50degs./X80 = TFOV. 0.63deg.
12mm = AFOV. 50degs./X107= TFOV. 0.47deg.
8mm = AFOV. 50degs./X160 =TFOV. 0.31deg.

You can no doubt now work out the figures in the absence of the focal reducer should you so wish to do so.

These TFOV figures are, as said, based on the assumption that the 24mm and the 20mm EPs in the "Zoom" have an AFOV of 68degs. the other three, 50 degs. This may not be quite the case but it's probably about right.

Hope my maths are right ! !

Best regards,
Tel