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Jan2-13, 01:50 PM
Drakkith's Avatar
P: 11,890
Both eyepieces cause the light rays to exit parallel to one another. (When focused correctly) This allows you to use your eye and focus at infinity, which requires no flexing of your lens and doesn't tire your eye out.

In A) the eyepiece is a Ramsden. The light comes to focus at the focal point of the objective, then begins to spread out again until it enters the first element of the eyepiece. The element bends the light towards the 2nd element and after exiting the eyepiece the light is now collimated and ready to enter your eye.

In B) the eyepiece is a Huygens. The converging light cone doesn't come to focus before entering the first element of the eyepiece. However the end result is the same. The light exits the eyepiece collimated and ready for viewing with your eye.