Eyepiece Showdown: Plossl vs. Kellner - Unveiling the Differences
Amateur astronomers often receive 3- to 4-element eyepieces with their first telescopes, typically Ploessl or Kellner models. These eyepieces, which have been around since the mid-19th century, were once considered top-tier, but modern advancements have relegated them to budget options due to advancements in optical manufacturing and design.
Design and Construction
The Kellner eyepiece design, invented in 1849, consists of three lenses: a cemented convex doublet where light enters and a single convex eye lens at the viewing end. The Plossl design, invented as an evolution of the Kellner, uses a second cemented doublet lens in place of the Kellner's single lens as the eye lens.
Market Dominance and Alternatives
Kellner eyepieces were once a staple in the astronomy community, but their dominance waned in the 1980s due to the advent of computerized ray tracing software and more efficient manufacturing techniques. As a result, Plossl eyepieces have risen in popularity and dominate standard eyepiece kits included with beginner telescopes.
Optical Performance
While Kellner eyepieces have a slight edge in resisting internal reflections, they suffer from more chromatic aberration and astigmatism at the edges of the field of view compared to Plossls. Both designs are generally affordable but may vary in price based on factors like brand, quality, and focal length.
Buying and Upgrading Considerations
While Plossl eyepieces are generally the better choice from a performance standpoint, they may not be worth upgrading from Kellner if you are already using fairly nice Kellners. Cheaper Kellner and Plossl eyepieces may sacrifice optical quality, but higher-end models from companies like Tele-Vue and Masuyama can still be found.
Modern Alternatives
While Plossl and Kellner eyepieces remain popular, they are not the only good options available. Modern eyepieces like the Goldline series, Celestron Ultima Edge, and Explore Scientific 82-Degree provide wider fields of view, sharper images, and better aberration correction compared to traditional Plossl and Kellner eyepieces, making them worth considering.
Distinguishing Eyepieces
Manufacturers' labeling can be inconsistent when it comes to inexpensive eyepiece designs. Kellners are usually labeled as "K," "SMA" (Super Modified Achromat), or occasionally "A.R." (Achromatic Ramsden). Plossls are usually "PL" or "P," though the term "Super Plossl" is popular. In the absence of the word "Plossl," it can be generally assumed that a "Super" eyepiece is not a Plossl.
- Beginner astronomers often receive Kellner or Plossl eyepieces with their first telescopes, which are part of the field of optics used in astronomy.
- In the science of astronomy, Plossl eyepieces have surpassed Kellner in popularity due to advancements in technology and manufacturing, despite Kellner eyepieces being less prone to internal reflections.
- When considering upgrading eyepieces, a beginner using good quality Kellner eyepieces may not find it necessary to move to Plossl, but modern alternatives like the Goldline series or Explore Scientific 82-Degree offer wider fields of view, sharper images, and better aberration correction.
- In the world of technology and science, understanding the differences between eyepieces, such as Kellner and Plossl, is important for making informed purchasing decisions in the field of astronomy.
