Lunt 7.2mm to 21.5mm zoom

The 7.2mm to 21.5mm focal length range of this Lunt Solar zoom eyepiece has been chosen specifically to complement the focal lengths of the various Lunt H-alpha refractors for solar observing. That said, it should also be noted that the eyepiece works equally well for daytime terrestrial observing and nighttime observing with virtually any standard (non-solar) telescope. For these latter situations, the Lunt zoom offers the convenient ability to precisely match the observing magnification to daytime seeing conditions, as well as a virtually infinite number of medium to high power nighttime magnifications in a single reasonably-priced eyepiece.

As with virtually all zooms, the apparent field of view of this Lunt Solar zoom decreases somewhat as the focal length increases. This generally results in a 20% narrower field of view at low powers than you can achieve with similar focal length single magnification eyepieces. This is just the reverse of what most people expect from eyepieces - which is a wider field at lower powers, where you're usually observing larger objects that don't need as much magnification to fit in the eyepiece field. The Lunt Solar zoom's apparent field of view ranges from 53° at the highest power 7.2mm focal length to a 40° field at the lowest power 21.5mm focal length.

Eye relief of the zoom's 7 lens/4 group optical system is specified at 15mm. The eyepiece is fully multicoated. It has a soft rolldown rubber eyecup for eyeglass use. A safety groove cut into its barrel will catch the thumbscrew of your focuser or star diagonal and keep the eyepiece from falling to the ground should the thumbscrew accidentally loosen during use. The power change band on the eyepiece uses a ribbed gripping surface that makes it easy to make small power changes, even in cold weather when wearing gloves or mittens.