Binocular Viewers

Until recently, many new observers inquired about binocular viewers (binoviewers), but few actually bought them, primarily due to the expense.  This is starting to change, with less-expensive binocular viewers becoming available.  As with anything, you get what you pay for, so the best binoviewers will still be pricey.  Also, you have to buy two of… More »

Zoom Eyepieces

Zoom eyepieces offer a convenient method of changing magnification without having to use multiple eyepieces.  Unfortunately–there being no free lunch and all–there is a trade-off in optical quality when using a zoom eyepiece. Above:  A typical zoom eyepiece, TeleVue’s 8-24mm Click Stop Zoom   Advantages of Zoom Eyepieces The main advantage of a zoom eyepiece… More »

Long Eye Relief Eyepiece

One of the drawbacks to standard eyepiece designs is that at short focal lengths (high power on most telescopes), the eye relief is very short.  Eye relief is the distance the observer’s eye must be from the eyepiece lens (see diagram below).  Short eye relief makes viewing quite difficult, especially for eyeglass-wearers. Above:  Eye relief… More »

Wide Field Eyepieces

Wide field eyepieces (with apparent fields greater than 50°) were originally invented for military applications during World War I.  The Erfle design consists of 5 or 6 lens elements and give an apparent field of 60-70°.  They are relatively inexpensive but suffer from distortion and astigmatism at the edge of the field of view.  They… More »

Standard Eyepieces

Standard eyepieces are relatively inexpensive designs which function very well.  These include the types of eyepieces normally included with telescopes.  The apparent field of view of a standard eyepiece is usually in the range of 40-50°. Early Eyepiece Designs The first telescope eyepieces, such as those used by Galileo, consisted of a single lens.  (See… More »

Understanding Eyepieces

Eyepieces determine the magnification and field of view of a telescope.  Different eyepieces are used to view different objects.  Some objects, such as nebulae and star clusters, appear quite large and are best viewed at low magnifications (which give a wider field of view), whereas planets appear very small and are normally viewed with high-magnification… More »