What does K9MM field mean?

Question: I have a telescope that I got for free and one of the eyepieces says K9MM field and what looks like 48 degrees. What does that mean?

Answer: K stands for Kellner. Kellner eyepieces have three elements, and are generally OK for lower power observing if you're not very fussy. 9mm is the focal length of the EP. To calculate the magnification it will give, divide the focal length of your scope by the focal length of the EP. 9mm is fairly high power, so the quality of the views won't be as good as some other eyepieces, though still OK for casual looking. Field means "Apparent Field Of View". This is how much sky the eye sees when it looks through the eyepiece alone. 48 degrees is respectable.

Related Questions

Related Items