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Both the Kellner and Plossl eyepieces have their pros and cons, with the Plossl winning out in quality while the Kellner is less expensive
Telescopes aren’t as simple as they seem and actually have so many parts and pieces that it can be overwhelming for new sky watchers. One of the most important pieces of the telescope is the eyepieces, and two of the most famous types of eyepieces are the Kellner and Plossl eyepieces.
Although both eyepieces are some of the most common, there are distinct differences between them. Let’s explore some of the things that make these 2 eyepieces unique.
How Does a Kellner Eyepiece Work?
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In 1849, mechanic Karl Kellner invited the Kellner eyepiece by attaching 3 lenses together. His goal was to do away with some of the problems with more simplistic eyepieces of the time.
The Kellner lens was the first achromatic eyepiece, meaning that it didn’t break down light into component colors. This meant the Kellner eyepiece showed colors truer than any eyepiece before it.
Kellner eyepieces work by using three glass pieces: a double, which is two lenses together, and a single, which is a single lens. It has a field of vision of 30 to 50 degrees.
The Kellner eyepiece is simplistic compared to some of the more modern eyepieces on the market, but it is a great starter lens for amateur astronomers and offers a clear and accurate picture.
How Does a Plossl Eyepiece Work?
Not long after Karl Kellner invented the Kellner eyepiece, Simon Plossl invented his own eyepiece in 1860. Unlike the Kellner eyepiece, which contained 3 pieces of glass, the Plossl contained 4 pieces.
The Plossl eyepiece is the superior of the two eyepieces in our article because of how it improved on the more simplistic Kellner design. It has a larger field of view and is also achromatic, with almost no color aberrations.
The Plossl eyepiece contains 2 double lenses for a total of 4 lenses which are all identical to each other. Even today, the Plossl eyepiece is considered one of the best eyepieces around and is used by amateurs and experts alike.
The downside to these improvements is that the Plossl is more expensive than the Kellner. For seasoned astronomers, this cost difference is negligible, but it can make newer sky watchers shy away from this expensive piece of equipment.
That being said, if you want to dive deeper into home astronomy, a quality Plossl eyepiece is a must.
Differences Between Kellner and Plossl Eyepieces
When comparing eyepieces, the differences can get confusing quickly. Below are the key differences between the 2 eyepieces and how they will affect your viewing experience.
Number of Lenses
A Kellner eyepiece has 3 lenses, while a Plossl has 4.
A Kellner eyepiece has 1 double lens and 1 single lens. These lenses are connected together.
The Plossl eyepiece has 4 lenses, consisting of 2 identical double lenses. Because of this setup, you might also hear a Plossl eyepiece referred to as a symmetrical eyepiece.
Eye relief refers to the distance between your eyes and the eyepiece at which you may easily view the entire image. Neither the Plossl nor the Kellner eyepiece has great eye relief when compared with the more powerful eyepieces, but the Plossl comes out on top in the end.
The Kellner’s short eye relief can make it difficult to use comfortably use, especially for people with glasses. Plossl’s eyepiece has a slightly longer eye relief, making it easier to use, but even this more costly lens will have problems at higher power ranges.
Field of View
Because of its 4 lens design, the Plossl eyepiece has a better field of view than the Kellner.
The field of view refers to the largest viewable region that your gadget allows you to observe. A Kellner eyepiece has a field of view of 30 to 50 degrees, averaging out to 40 degrees. This limited field of view is because of the Kellner’s 3 lens setup.
With its symmetrical 4 lenses, the Plossl has a superior field of view of 50 degrees on average.
Similarities Between Kellner and Plossl Eyepieces
There aren’t nearly as many similarities between the Kellner and Plossl eyepieces as there are differences. Both eyepieces were invented in the mid-1800’s, addressing the problems with color and spherical aberrations found in eyepieces of the time. They went on to correct these problems in significantly different ways.
The biggest similarity between Kellner and Plossl eyepieces is that they are both constructed with achromatic lenses.
Achromatic lenses that lessen chromatic aberrations. Simply put, with achromatic lenses, the colors you see through the lens will be more true to life. Achromatic lenses aren’t perfect, and more modern eyepieces will have even better color correction, but for the time they were invented, the Kellner and Plossl lenses were groundbreaking.
Why Pick One Over the Other?
If you’re just starting out with astronomy and want to keep costs low, go with the Kellner eyepiece.
Even though the Plossl eyepiece is of higher quality in a lot of ways, for amateur astronomers the differences won’t really be noticeable. For this reason, we recommend starting out with a Kellner lens.
If you’re upgrading your eyepiece, go with a Plossl eyepiece. More experienced sky watchers will be able to tell the difference between the two lenses and the Plossl lens will fit your needs for a long time to come.
It’s hard to put down the extra money for an eyepiece when a Kellner is cheaper, but once you buy a quality Plossl eyepiece, you won’t have to purchase another for a very long time. A nice Plossl eyepiece is one of the best eyepieces you can get for home star viewing.
Both the Kellner and the Plossl eyepiece are great choices for beginners, but once you become more serious about your telescope, Plossl is the way to go.
Both eyepieces have achromatic lenses, but with a higher field of view and better eye relief, the Plossl is the better of the two eyepieces. That being said, the Kellner is still a nice eyepiece that is perfect for beginners, and is reasonably priced.
For other eyepiece options to take your stargazing to the next level, check out our best eyepiece choices here.