For a few years now I have been using a laser to help determine 2 things about an eyepiece: light transmission and glass purity/cleanliness.
Using my green laser to help judge light transmission I simply shine the beam at close range into the eyepiece and see how bright the reflections are. The better coated eyepieces have dimmer reflections than the inferior coated eyepieces. Sometimes the differences are obvious. My Pentax XWs show the dimmest relections of all with the Naglers a close 2nd.
To determine glass purity and cleanliness, I shine the green laser on the white wall maybe 5-10 feet away and hold the eyepiece up so that the bright pointlike reflectoin is centered in the fov. I then look through the eyepiece and look for any dark splotches and other impurities. Apparently clean eyepieces can look filthy. Also any inconsistencies in the coatings will be obvious as well.
One premo eyepiece I had showed the whole fov to be splotchy even after cleaning all accessable surfaces. This surprised me and explained why contrast was not 100% as good as it should have been. Casual inspection did not reveal any problems.
I should mention that this test is so sensitive than almost no eyepiece will show no impurities whatsoever but a couple of tiny spots will appear even on a new premo eyepiece. Even after cleaning an eyepiece and then using it carefully for one observing sesssion can reveal all tiny dust particles that accumulated during the session.
I hope these ideas can help some of you a little in evaluating eyepieces in the future.
Using my green laser to help judge light transmission I simply shine the beam at close range into the eyepiece and see how bright the reflections are. The better coated eyepieces have dimmer reflections than the inferior coated eyepieces. Sometimes the differences are obvious. My Pentax XWs show the dimmest relections of all with the Naglers a close 2nd.
To determine glass purity and cleanliness, I shine the green laser on the white wall maybe 5-10 feet away and hold the eyepiece up so that the bright pointlike reflectoin is centered in the fov. I then look through the eyepiece and look for any dark splotches and other impurities. Apparently clean eyepieces can look filthy. Also any inconsistencies in the coatings will be obvious as well.
One premo eyepiece I had showed the whole fov to be splotchy even after cleaning all accessable surfaces. This surprised me and explained why contrast was not 100% as good as it should have been. Casual inspection did not reveal any problems.
I should mention that this test is so sensitive than almost no eyepiece will show no impurities whatsoever but a couple of tiny spots will appear even on a new premo eyepiece. Even after cleaning an eyepiece and then using it carefully for one observing sesssion can reveal all tiny dust particles that accumulated during the session.
I hope these ideas can help some of you a little in evaluating eyepieces in the future.
