What does a "flat-field" eyepiece like the Ultima Edge 18mm do?
A flat-field eyepiece corrects for the optical aberration known as field curvature, which can make stars at the edge of the view appear out of focus or distorted. The Ultima Edge 18mm is designed to deliver a sharp, focused image from the center all the way to the edge of its 65° field of view.
Is the Ultima Edge 18mm good for viewing planets like Jupiter in a Schmidt-Cassegrain telescope?
Yes, the 18mm focal length provides medium-high magnification that is excellent for planetary viewing in a typical f/10 Schmidt-Cassegrain Telescope (SCT). The flat field will ensure that Jupiter's moons (the Galilean satellites) are as sharp as the planet itself, even when they are near the edge of the field.
How will the Ultima Edge 18mm perform on open clusters like the Pleiades (M45) with a fast refractor?
In a fast telescope (f/5-f/7), the benefits of the flat-field design are even more pronounced. The Ultima Edge 18mm will keep the stars of an open cluster like the Pleiades sharp across the entire 65° field, avoiding the distracting "seagull" shaped stars (astigmatism) that can appear at the edges in simpler eyepiece designs.
What does it mean that the Ultima Edge eyepieces are "parfocal"?
Being parfocal means that you can switch between different eyepieces in the Ultima Edge series and they will remain in focus. This saves time and makes observing more efficient, as you don't have to make major adjustments to your telescope's focuser every time you change magnification. Note that the 24mm Ultima Edge is not parfocal with the rest of the series.
Can I use filters with the Ultima Edge 18mm eyepiece?
Yes. The 1.25" mounting barrel is internally threaded to accept all standard 1.25" astronomical filters, such as moon filters, nebula filters, or color filters for planetary observing.
Is the 20mm eye relief on the Ultima Edge 18mm suitable for eyeglass wearers?
Absolutely. With 20mm of eye relief, most eyeglass wearers can comfortably see the entire 65° field of view without having to press their glasses against the eyepiece. The fold-down rubber eyeguard also helps to set the correct distance and block stray light.
