I don't think you can actually injure your eyes viewing the Moon with any telescope an amateur is likely to have, for two reasons:<br /><br />1.) The Moon is so much dimmer than the Sun that it would require a very large telescope to really do damage.<br /><br />2.) As a general rule, the larger a telescope is, the longer the focal length and the higher the minimum magnification is. This doesn't sound that important, but keep in mind that doubling magnification reduces light intensity per unit area to a fourth of its previous value. Therefore, the Moon looks brighest at low magnification, and dimmer with higher magnification. <br /><br />That said, looking at the Moon through a large telescope can be quite uncomfortable, so a filter will make viewing much more pleasant. It will also enable more details to be seen, since it will prevent features from being washed out by glare.<br /><br />For the record, according to my Orion catalog, good filters for viewing the Moon are neutral density filters, polarizing filters, and yellow or yellow-green filters. All of them thread into the eyepieces you're using. I can personally vouch for the utility of a yellow-green filter for Moon watching; sometimes, it can make the disk seem almost 3-D. <img src="/images/icons/smile.gif" />