Eyepiece Types

 

In the following table we have listed some of the most common eyepiece types with their pros and cons. The graphics at the left side are to be understood as an example of the eyepiece type, there are a lot of modifications on the market. As an example, the Kellner design is also available as a reversed Kellner, which means, that the two-lens element is at the bottom side. Furthermore one can manufacture any design in a careless way, that you do not have to think about inherent pros and cons - but for that we do our testing.

Additionally something about the viewing distance (the eye relief): as a rule of thumb eyepieces have an eye relief of about 2/3 of their focal length. This is uncomfortable, if the focal length is less than 6 to 10mm, as you have nearly to touch the eyepiece with your eye. Therefore modern Long Eye Relief eyepieces combine e.g. a Barlow lens with a Ploessl design, which leads to an eye relief of about 15 or 20mm for all focal length. However, adding more lenses will have the effect of more stray light, loss of contrast and generally image degradation - at least if not very careful manufactured. Such eyepieces should not be used with an additional Barlow lens.

 

 

Design

Type

Pros

Cons

 

Huygens

 

Simple, two-lens type

 

Cheap

 

 

Apparent field of view is small (ca. 30-35°), not achromatic

 

Kellner

 

 

Also cheap

 

not achromatic, small field of view (about 45°), eyepieces with long focal length not recommended for optics of F/5 or F/4

 

 

Orthoskopisch

 

4-lens design

 

Nice image quality, achromatic

Often used for planetary observations

 

Small field of view (about 35-40°)

 

Ploessl

 

Standard in modern astronomie

 

Relatively cheap to have, very good image quality

 

Field of view just about 45°, below 10mm focal length small eye relief

 

 

Super Ploessl

 

modified Ploessl, 4- or 5 lenses. Often just Ploessl with an added “Super“

 

Field of view about 52°, if really a modified Ploessl. Contrast and image quality very good

 

A little bit more expensive than Ploessl, eye relief like Ploessl

 

Erfle

 

Standard design for wide angle eyepieces

 

Nice apparent field of view (about 65°), not to expensive

 

 

Near to the edges not good with fast optics (F/5, F/4)

 

Nagler and Super- or Ultra- Weitwinkel

 

Very big apparent field of view (up to 85°). Very good image quality possible, but depends strongly on the manufacturer. Can be build up for use in F/4 and F/5 - but expensive in that case.

 

 

Nagler: Very expensive and remarkable distortion

Pentax:

Very expensive.

Others:

If cheap: Do not use with fast telescopes.

 

 

 

 

Thanks to Skyproject here: I “loaned“ the graphics from there. I would have asked them for a permission, but there was not contact address given…