Slightly more expensive

Slightly more expensive, but vastly better in ridding chromatic aberration is the Kellner eyepiece. The better color correction comes from the fact that the eye lens is achromatic though the field lens is still simple. A derivative of this type called the Erfle has an extra achromatic lens inserted between the eye lens and the field lens to yield a much larger field of view. However, you will usually pay for this greater field of view by getting more astigmatism.

Toward the higher end of the cost range is the orthoscopic eyepiece. It offers excellent correction not only of chromatic aberration, but also astigmatism and coma.

Having the best correction of all standard eyepiece types, the Plössl is also usually the most expensive and will typically have a wider field of view than an equivalent orthoscopic.

But regardless of the type of oculars you choose to use, I recommend that your set of eyepieces include the following:

1) A low power eyepiece. 35 mm to 25 mm focal length. The exact focal length that you should get should be the one that yields an exit pupil of 5mm or less when the eyepiece is used with your particular telescope (see above explanation of how to figure exit pupil). Use this ocular while trying to acquire an object because the greater field of view makes this task easier. Also, such an eyepiece will make deep sky objects appear brighter.

2) A medium power eyepiece. 15 mm to 10 mm focal length. Great for observing brighter deep sky objects such as globular clusters and nearer nebulae. Also use these to observe the moon and planets under moderate viewing conditions.

3) At this point many would recommend a high power eyepiece of 8 mm to 5 mm focal length for observing the moon and planets in those rare times when conditions are acceptable for high power. I agree that you need a magnification this high under such conditions, but as I shall point out to you shortly, there is a better way to reach these magnifications without buying a special eyepiece!

Point number three leads us to a discussion of an interesting animal called the Barlow lens. This accessory will cause an eyepiece to deliver two to three times as much magnification as it normally would! I suggest that you purchase one of these instead of a very high power eyepiece. To see my reasons for saying this, let us compare the view through two identical telescopes both being used at the same high magnification and viewing the same object. One has only a very short focal length Plössl ocular. The other telescope achieves an identical magnification using a medium focal length Plössl and a Barlow.

Image contrast will usually be significantly lower in the telescope with the high power eyepiece. Also if the telescope’s focal length is relatively short for its size, coma will be more noticeable.