A brief history of eyepieces

Ramsden, Huygens and Kellner are the oldest designs. Their designers were Christian Huygens, Jesse Ramsden and Carl Kellner. The Huygens dates back to the mod 1600's. These designs are rarely used thesedays, as there are better alternatives. Kellners can make very good lunar/planetary viewing eyepieces, in a suitable telescope (slow achromatic refractors eg 4"/F12 etc, also small Maksutovs), but their eye relief is very tight.

In 1860 came the Plössl design invented by Georg Simon Plössl. This design took eyepiece performance to a new level although it's advantages and improved performance were not recognised until many years after it was designed. The Plössl is still in wide use today. It is one of the best designs and provides very sharp high contrast images on axis, in scopes as fast as F4. Since the original design their have been many "modified" Plössl designs produced. All work very well. The Brandon is a very good one. As are all the 5 Element Plössl variations. These 5 element Plössls are also known as the Masuyama design. Some of these currently produced include the Celestron Ultimas, Antares Elite and the Parks Gold series. The Takahashi LE series use a slightly different 5 element design and are outstanding performers. The drawbacks of all Plössl variants are an AFOV limited to between 50 deg and 55 deg, and reducing eye relief as the focal length of the eyepiece reduces.

In 1880 came the Orthoscopic invented by Ernst Abbé, who was an employee of Carl Zeiss. "Orthoscopic" means free of optical distortion. The Orthoscopic eyepiece offers very similar performance levels to the Plössl and like the Plössl it is one of the best designs and provides very sharp high contrast images on axis, in scopes as fast as F4. It's drawbacks are an AFOV limited to between 45 deg and 50 deg, and reducing eye relief as the focal length of the eyepiece reduces. However, the eye relief in an Orthoscopic for a given focal length is slightly better than it is in a Plössl. Orthoscopics are still my favourite lunar/planetary eyepieces. The University Optics HD orthos are an excellent eyepiece for not a lot of cost. The Zeiss orthoscopics which went out of production about 5 years ago are superb, they offer unsurpassed levels of lunar and planetary performance. But alas they are very expensive (about $US3,000 for a set of 5) and rarely offered for sale on the 2nd hand market. They are almost unprocurable.

World War I came along and this highlighted a need for "widefield" eyepieces in both telescopes and military style binoculars. From 1915 to 1940 many widefield eyepieces were developed. All were designed to work in the slow optical systems of the period and don't do so well in todays very fast F-ratio systems.

In 1923 Albert König, an employee of Carl Zeiss developed the "original" König I design which is a variant of the orthoscopic design. There were several subsequent modifications to the König. These are still manufactured today and work very well in medium/slow telescope systems. Their downside is tight eye relief as the focal length reduces and soft edge performance in faster telescope systems.

In 1925 Heinrich Erfle, another employee of Carl Zeiss, designed the Erfle I. There were also several subsequent modifications to this design. Like the Konig they are still manufactured today and work well in medium/slow telescope systems. The Erfle is probaly the most widely modified and "butchered" eyepiece design of all. There have been many variants produced, which closely resemble the original designs. The current 80 deg "Widescan" series are based on a modified Erfle design. Like the König, their downside is tight eye relief as the focal length reduces and soft edge performance in faster telescope systems.

Between the late 1920's and 1975 not a lot happened. There was some modifications to existing designs and a few new designs, none of which are currently in production. These designs include the Galoc, Bertele and the Zeiss Astroplanar.

Note that just about everything to this point has originated in Europe.

In 1975 Dr David Rank, an employee of Edmund Scientific, modified the Kellner design and came up with the RKE. RKE stands for Rank Kellner Eyepiece. It has also been termed by amateur astronomers as a "reversed kellner", which is exactly what it is. These are excellent planetary eyepieces but like their parent design,have some faults. They do not work well in fast F-ratio systems and eye relief is short.

In 1979 Al Nagler the owner and founder of Televue in the USA, designed the original Nagler. This was an Ultra Wide field (82 deg) design that offered exceptional performance in telescope systems as fast as F4, eye relief was quite good compared to existing designs. Preceeding the Nagler was the Televue Widefield and then the Televue Panoptic. The TV widefields were replaced by the Panoptics which are still manufactured by Televue to this day. These 3 eyepiece designs from Al Nagler changed the whole expectation of eyepiece performance of amateur astronomers. Since the original Nagler there have been 4 new variations T2,T4,T5 and T6. The T4's,T5's and T6's are in current production. The Nagler really raised the bar in terms of performance in fast telescope systems and FOV. Several companies have subsequently produced similar performing eyepieces with good success, albeit with a slightly narrower FOV, trading the FOV off against aberrations and eye-relief. These include Vixen, Pentax and Denkmeier. While Meade have produced some widefield designs they didn't do anything new IMO.

Written by John Bambury 26/04/2007