Several items:

1. The focal length of the telescope is a function of 'how far back' the
focal plane is. When I 'play' with my CCD on my 10" f/6.3 a 2" change in
distance changes the focal length from 1600mm to 1800mm.

2. If you assume a focal length of 2900 for your system you get very good
agreement with your observations.

3. The eyepiece focal length and apparent fields are nominal values (like
the 2500mm focal length of your telescope). I would suspect that a longer
telescope focal length and some minor variations in eyepiece focal lengths
and apparent fields would be sufficient to explain your observations. Note
the telescope focal length variation is the largest effect.

[So I do not think there is evidence yet that the eyepieces are
mis-represented]

4. A faster way to get the field of view is to go to a star and go north
until it is at the edge and note the declination, then go south until it is
at the edge and subtract the new declination from the initial declination.
Always works in polar mode. In Altaz you need to be on the meridian or anti
meridian for this to work. Polaris would be a good star for Altaz mode.



Ralph

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