Two-Inch Eyepieces from Baader Planetarium, Celestron, Explore Scientific, Meade, Orion, Pentax, Stellarvue, Takahashi, Tele Vue, Vixen and William Optics
By Chuck Hawks
Some telescopes, such as the Celestron Edge HD 9.25", 11" and 14" CAT's come with two inch star diagonals and Celestron SCT's that come with the standard Celestron 1.25" visual back will accept the replacement Celestron 2" star diagonal that threads directly onto the rear cell of the telescope. Most of the better (especially ED and APO) refractors from many manufacturers are supplied with 2" focusers. Vic Maris of Stellarvue, for example, told me that most of his customers were using two-inch oculars.
Two-inch oculars typically offer a wider field of view in focal lengths over about 32mm than is possible with 1.25" mounting barrels. Thus, they are most advantageously used in long focal length eyepiece applications. There are, however medium and short focal length 2" oculars available. Many of the oculars with focal lengths shorter than about 24mm are designed to work interchangeably in either 2" or 1.25" holders, making them dual-size oculars. The field stop of such oculars, of necessity, is smaller than 1.25", meaning that there is no optical advantage to using them in a 2" focuser or star diagonal, although it may be more convenient to do so. The primary disadvantages of two-inch eyepieces are their cost, size and weight; ditto for the two-inch star diagonals they require.
If you are looking to purchase two-inch oculars, there are two ways to go. First, buy a packaged set, such as the Celestron two-inch Eyepiece and Filter Kit ($249.95 from Optics Planet) pictured above. This includes three inexpensive E-Lux series oculars, a two-inch star diagonal, a set of seldom used Wratten colored filters (no moon filter, unfortunately), a simple Barlow lens and a handy hard case in which to carry it all. This is the easy approach and it doesn't require much thought. The price is right, but the drawback is that these oculars are three element Kellner designs that are inferior to most of the two-inch oculars sold individually.
The second option is to carefully choose higher quality oculars that fit your specific needs. This costs more and requires some thought and research. In addition, you will need to purchase a case to carry your two-inch oculars and accessories; the Pelican 1450 medium size hard case with foam interior is usually about the right size for the purpose ($93.99 at Optics Planet). Needless to say, this is the approach I recommend and I compiled the list that follows to assist with the research.
All prices are approximate 2011 discount retail from major online dealers, such as Optics Planet, Oceanside Photo & Telescope and Woodland Hills Camera & Telescope. Prices vary among dealers and change frequently.
56-50mm focal length
42-40mm focal length
38-34mm focal length
32-30mm focal length
28-24mm focal length
22-20mm focal length
18-17mm focal length
14-12mm focal length
10-8mm focal length
6-3.5mm focal length
Copyright 2010, 2012 by Chuck Hawks. All rights reserved.