[jbloggz (Joe)]

I recently bought my first telescope (second hand 12" dob) and it came with a handful of (pretty average) eyepieces.

I'd like to now put some money into a couple of decent eyepieces and decided to first get a high power one so I can get a good look at the planets (saturn and jupiter especially) as well as the moon.

I was thinking that the 7mm william optics UWAN would be a good choice since it's seems good value (~$200) and has a large FOV (82 degrees) which I imagine will help with manual tracking of the planets.

Then I found the following info about it:
Eye relief = 16mm
Eye lens diameter = ~20mm

After a bit of trigonometry, this doesn't quite add up..... It's not possible to see the entire FOV at the eye relief distance. You can only see about 64 degrees before hitting the edge of the eye lens. So you would have to move your head around to see the entire FOV???

Is this common with large FOV eyepieces? It seems the longer focal length ones have much larger eye lenses, so prehaps it's just an issue with shorter focal lengths. Why can't they have bigger eye lenses? Ideally I'd love to be able to position my head in a single spot and just move my eye to see the entire FOV. This would give a much more immersive feeling.

Thanks to anyone who can shed some light on this.