This eyepiece can serve any amateur astronomer who wants to make their own measurements of separations and positions of binary stars or the extents of features on the Moon. Given some facility with this little tool, you could probably measure anything you can see.
It is called a “Log Pot Illuminator” because the brightness control is logarithmic: you have to turn the knob much to make it a little brighter or a bit dimmer. In other words, it delivers very fine control. (“Pot” is short for “potentiometer” an older word from the early days of electricity for a volume control, gain, or variable resistance.) You sharpen the image of the scales by turning the top screw mount of the ocular. It is very simple and intuitive. You focus the eyepiece as you would any other, by focusing your telescope.
My three nights of use did not go well.
First of all, things move pretty fast. The first two nights, my telescope was a Meade 10-inch “Advanced” Ritchey-Crétien f=2500 mm fork mount (right ascension and declination) with manual controls. The challenge of targeting was like trying to snatch a housefly out of the air. My first projects were to measure the diameter of Mars, the width of the Trapezium in M42, and the separations of the brightest stars in the Pleiades. My eyes could not move fast enough to measure the objects against the tics. You might be more agile. But this really required a motorized drive to hold the telescope on target or a camera to record the view or both.
Another of the procedures is to align the reticle with the celestial equator. The way to do that is to find a star and position the reticle so that the star tracks along the horizontal metric bar. I chose Rigel. It is close to the celestial equator (declination −08.2°). Manipulating the reticle and the two controls was a juggling act. It likely would have gone better with the electric drive control paddle. Turning two knobs and twisting the reticle was hard work for a creature without a third manipulator.
The next night, I tried a smaller telescope, an Explore Scientific 102 mm refractor f=660 mm with First Light mount (simple tilt-pan XY). I ran into a problem that I experienced earlier with this instrument: the focal tube draw cannot be short enough. In the earlier failure, I was viewing Venus; and to cut the glare, even a moon filter was not enough. I added another filter and hit a hard stop. The draw would not go in far enough to focus. (That morning, I was able to use two filters with my 70 mm National Geographic refractor.) The same thing happened here. With the diagonal in place, focus was impossible. Without the diagonal my posture was difficult to obtain and impossible to hold. So, I gave up.
I have one other unresolved problem. I still do not know how to change the battery. Baader has helps on their website, but no answers to the questions. They tell you exactly which type of cell to use (standard US NEMA number). They do not tell you where it goes. When I unscrewed the two pieces of the reticle itself—not the illuminator—I found a wire (which I accidentally tore out and had to re-solder.) So, at this point, I do not want to struggle with it any more. It is packed away. If I buy a telescope with a motor drive or if I buy a camera for astrophotography, I may take this up again, but I will most probably sell it at a discount to someone else in my local astronomy club and get my measurements from standard stellar survey catalogs.
