Have a look at the Baader Hyperion 8-24mm zoom.
http://www.alpineastro.com/Eyepieces...ories.htm#Zoom- Continuously variable focal length, with click-stops at 8, 12, 16, 20, 24mm. Remains approximately parfocal across zoom range. Click-stops enable precise focal length matching for bino-viewer use (please note: barrel diameter of the zoom is 57mm, so it may not work in binoviewers for users with narrow interocular separations).
- Wide field. The field of view is 68degrees at the 8mm setting, and 50 degrees at 24mm.
- Excellent viewing comfort. The eye relief of 12-15mm, large eyelens, and freedom from kidney beaning and blackouts result in a high level of comfort and ease-of-viewing, at all focal lengths.
Robert