Posted By Dan D DuBal
I juggled three different apertures with the Explorer: full aperture, of course, plus an effective 40mm, provided by the objective cap’s aperture mask. I also borrowed my Pentax 75’s objective cap whose mask yields an effective aperture of 50mm. With the scope’s inherent 800mm focal length (f/13.3), the 40mm & 50mm masks yield effective focal ratios of f/20 & f/16 respectively.
Stock eyepieces included two “Huygens” (20mm & 12.5mm) & a 4mm “Symmetrical Ramsden.” Believe it or not, the Ramsden (though certainly not symmetrical) is actually a decent eyepiece. Its housing has a telltale “circle-T” logo; maybe that’s a factor. None of the stocks is a “true” representative of its parent design. The Ramsden’s eye relief is far better than it should be, & both Huygens employ field stops which restrict their fields (thus increasing eye relief). However, other aspects of their designs seem “correct” (elements’ spacing & relative focal lengths, position of image plane, etc.).
In addition to the stock eyepieces, I fed the Explorer three others from my bonus menu: a Celestron 18mm Kellner, Takahashi 7.5mm LE (1.25-inch barrel/sleeve removed), & Pentax 6mm Abbe. With this group of eyepieces, the Explorer yields magnifications of 40, 44, 64, 107, 133, & 200.
Well, let’s dive right in. How did this vintage “trash” scope & its stock “garbage” eyepieces perform?