Eyepieces are commonly referred to by focal length and barrel diameter. The focal length of each eyepiece is printed on the eyepiece barrel. The longer the focal length (i.e.,thelargerthenumber) thelowertheeyepiecemagnification(i.e.,power)andthe shorter the focal length (i.e., the smaller the number) the higher the magnification. Generally,youwilluselow-to-moderatepowerwhenviewing. Formoreinformation onhowtodeterminepower,seethesectionon“CalculatingMagnification.”
Barrel diameter is the diameter of the barrel that slides into the star diagonal or accessory adapter. Your CR-150 HD refracting telescope can use eyepieces with both a 1-1/4" barrel diameter and 2" barrel diameter. To use a 2" barrel eyepiece, the 1 1/4" accessory adapter must first be removed. To do this, simply loosen the two chrome thumbscrews located around the focuser barrel (see figure 4-1) and remove the 1 1/4" adapter. Once removed, a 2" eyepiece or accessory can be inserted directly into the focuser barrel and secured with the two thumb screws.
| | 1 1/4" Accessory | Focuser Tension |
| | Adapter |
| Built-inT-Adapter | Screw |
| |
| Thread | | |
2" Focuser | |
Barrel | FocuserKnob |
| |
| Figure 4-1 |
Telescope Basics • 21
