Eyepiece characteristics

Eyepiece Characteristics: The various eyepiece types we carry are described below, with our subjective opinions of their performance in the following areas:

Number of lens elements: typically, more lenses in an eyepiece mean sharper images, and/or a wider field of view, and/or longer eye relief . . . although often with a loss of contrast compared to simpler eyepieces.

Sharpness: how well the eyepiece concentrates the light of a star into a sharp point at the center of the field.

Astigmatism: an aberration that turns stars into fuzzy oblongs instead of points, particularly towards the edge of the field.

Color correction: how free an eyepiece is from colored halos around stars at the edge of the field, false color in planetary images, or stars that change color as they move from the center to the edges of the field.

Ghosting: a flare of unwanted light around bright objects, or faint multiple images of bright objects, due to internal eyepiece reflections.

Field curvature: an inability to bring the center and edge of the field into focus at the same time, with the edge out of focus when the center is sharply focused and vice-versa.

Brandon: four lenses; medium to high power use with any telescope at focal ratios down to f/4; very sharp at the center (somewhat less so at the edges) for lunar, planetary, star cluster, and binary star observing; excellent color correction and contrast; very low astigmatism; the sharpest design currently available for eyepiece projection photography; very minor field curvature and ghosting; standard equipment on ultra-premium Questar Maksutovs.

Modified Achromatic, Super Modified Achromatic: computer-optimized versions of the three-lens design known as a Kellner (or achromatic Ramsden) that is supplied with many inexpensive scopes; for low to medium power use on telescopes with focal ratios down to f/6, but best above f/8; for general observing for the astronomer on a budget; acceptable to good sharpness at the center of the field with some astigmatism at the edge; good color correction; moderate ghosting; field curvature is noticeable, emphasizing the coma in fast focal ratio reflectors; telescope focal plane usually lies on the surface of the eyepiece lens nearest telescope (the field lens) so that any dust on the lens is in sharp focus, requiring extra care in keeping the eyepiece clean.

Vixen Lanthanum: six to eight lenses, using a lanthanum (rare earth glass) field lens; exceptional 20mm eye relief for eyeglass use, even in the exceptionally short 2.5mm focal length version; very short focal lengths use a built-in Barlow to achieve high power without reducing eye relief; optical performance approaches that of a Plössl at the center of the field (less so at the edges and with generally lower contrast), but with longer eye relief.

Nagler, Nagler 2, Ultra Wide Angle: Naglers have seven lenses, Nagler 2 and Ultra Wide have eight; up to three times the field area of a Plössl, but sharper edge to edge; up to ten times sharper at the edges than older wide angle designs such as Erfles; field is so wide you have to move your head from side to side to see all of it; more like looking out a window into space rather than looking through an eyepiece; superb color correction, with little ghosting or field curvature; some loss of contrast on planets due to many lens elements; short focal lengths use a built-in Barlow to achieve high power without reducing eye relief; medium to high power use down to f/4; for star clusters, nebulas, and galaxies with any scope, but particularly good with fast focal ratio reflectors.

Panoptic: six lenses, with an ED (extra low dispersion glass) lens for exceptional contrast and a very wide field; up to five times the field edge correction of older wide field designs; for low to medium powers down to f/4 with any telescope, although particularly good with fast focal ratio reflectors when combined with a Paracorr coma corrector; use of the 27mm or 35mm with a TeleVue 2" Big Barlow requires a Panoptic interface lens for the best performance, yielding an edge sharpness and lack of astigmatism that is comparable to a Nagler.

XL: proprietary Pentax wide field designs using five to seven lenses; very long eye relief; for low to very high power use down to f/4; all are fully Super Multi-Coated (SMC) and all use an ED (extra low dispersion glass) lens to minimize chromatic aberrations and astigmatism; usable for all types of observing, with all telescope types; good contrast and excellent center to edge sharpness; very little ghosting.

Plössl, Super Plössl: four lenses; from very low to high power use with all telescope focal ratios down to f/4; for lunar and planetary observing, nebulas, open clusters, or anywhere edge-to-edge sharpness and very good contrast is more important than an extra-wide field; excellent color correction; virtually no field curvature, astigmatism, or ghosting; work very well with any telescope type.

Wide Wide, Super Wide Angle: six lenses; 70% greater field area than a Plössl, and a Plössl’s edge to edge sharpness, but with somewhat less contrast; low to medium power down to f/4; for wide angle views of open clusters, large nebula remnants, clusters of galaxies, Milky Way star fields – wherever a very sharp, very wide field is called for; excellent color correction; virtually no ghosting or field curvature.

Takahashi: proprietary fully-multicoated five lens design with long eye relief; for low to very high power use to f/4; two shortest focal lengths use one ED (extra low dispersion glass) lens for exceptional contrast and color correction; usable with all scope types; suitable for all types of observing; very good sharpness and contrast; very little ghosting.

Ultima: four to seven lenses; short focal lengths use a built-in Barlow to achieve high power without reducing eye relief; for low to very high power use down to f/5, although with some field curvature at lower focal ratios; usable for all types of observing with all scope types; very good contrast, sharpness, and color correction, with only minor ghosting.


. . . our 34th year