Caption: Instead of making an occulting bar to help him see the moons of Mars, long-time observer Stephen James O'Meara fashioned a semi-circular filter using a Wratten #47 gelatin filter affixed in front of the field stop
on a medium-power eyepiece using a 11/a-inch outer-diameter O-ring.
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In those cases I used a 7-mm orthoscopic eyepiece with opaque photography tape covering half of its tiny field stop
, along with a 2x Barlow.
Observe when Sirius is highest in the south, use your highest magnification, hide Sirius's dazzle behind an occulting bar or the sharp edge of your eyepiece's field stop
, and wait patiently for moments of good seeing--but you know that already.
Baader, however, has used a larger field stop
than found in traditional orthoscopics, and this has increased the AFOV to 50[degrees].
If you look into the bottom of a simple eyepiece, such as a Plossl, you'll see a sharp-edged ring, or field stop
, located below the eyepiece's field lens.
Realizing that such perceptions are highly personal, I initially attributed it to the wide, yet defined, apparent field (I could see the entire circular field stop
without moving my eye--something I find comforting).
The system has six elements, 11 optical surfaces, and a field stop
. It sounds complicated, and in some ways it is.
To view Abell 12, I affix a thin strip of aluminum foil to the field stop
of my eyepiece with rubber cement.