Critically evaluating your own eyepieces is easy. Focus the eyepiece and examine the image. * Are the stars sharp points all the way from center to the edge of the field? If not, can you sharpen the edge of field stars by re-focusing slightly? If so, then the focal plane is curved. This could be an artifact of your objective, not necessarily the eyepiece. Try other eyepieces to try and determine which it is. * If the stars cannot be sharpened to points by refocusing, examine them closely. If the stars have little "wings" on them, you have a comatic image. If the star stretches out to a straight or slightly curved line that changes orientation by about 90-degrees as you move from one side of focus to the other, astigmatism is suspected. * Examine a fencepost or phone pole during the daytime through the telescope. As you move it from the center of the field to the edge, does it appear to bend inward or bow outward? If so, this indicates curvature of field and this is usually an eyepiece abberation. * Estimate how far from the center of the field the above abberrations begin to show up. If you don't see stretched, squashed or flared stars until you are almost to the very edge of the field, the eyepiece is pretty good. If it starts only a third or halfway out, the eyepiece has issues. Curvature of Field and Astigmatism are the biggest eyepiece offenders and easily checked for. These are the characteristics that most often determine if an eyepiece is "good" "bad" or "marginal". Spherical abberration and chromatic abberation are uncommon in eyepieces these days and typically indicate a sub-par objective, especially if a doublet refractor or undercorrected Newtonian. But if you notice spurious color that is not apparent in other eyepieces used with the same objective, these can be suspected. "Ghosts" are internal reflections, usually seen when a bright object is off-axis slightly. Modern camera lenses are notorious for ghosting, as are eyepieces with many elements. High price is no guarantee that the eyepiece will be ghost-free. This is usually an annoyance on planets, and during imaging only, and rarely seen when looking at the faint fuzzies visually. The above elements are there for anybody to see who looks through the eyepiece, and not really arguable. Eye relief and apparent field, on the other hand, while definitely properties that make an eyepiece easier or harder to use, are personal prefference items that will vary from individual to individual. * Eye relief can be judged on ease of use. Is there enough "breathing room" between your eye and the glass, or is your eye uncomfortably close to the eyepiece when in use? Eye-relief can be measured with a metric ruler by focusing on the moon, then measuring the distance from the glass to the round, tight "exit pupil" disk as seen on a card. Move it until the smallest diameter is achieved, then measure the distance. Usually, anything over about 18mm is considered "generous" and essential for eyeglass wearers. If it's under 12mm then it's considered on the tight side. EVery visual prescription is slightly different so what you need in the way of eye relief may be different from what your buddy needs. * Remember that as magnification increases, exit-pupil diamter decreases. For this reason, even those individuals with severe astigmatism can probably get along fine without their glasses at very high powers. We are only using the very center of our pupils in those cases and the "barrel correction" for astigmatism usually isnt needed. Try taking off your glasses for exit pupils below about 3mm, you may be pleasantly surprised. Exit pupil is determined by dividing the aperture of the telescope (in mm) by the magnification. The resulting approximation is the diameter of the exit pupil in millimeters. Evaluating eyepieces is a tad more involved than just looking at the image and making an aesthetic judgement. Wide-field has nothing to do with image fidelity and often contributes to abberrations, so judge critically and don't let yourself be "wowed" soley by the composition. Have fun, be honest with yourself, and good luck! __________________________________ Do you Yahoo!? New and Improved Yahoo! Mail - Send 10MB messages! http://promotions.yahoo.com/new_mail