Quote:
Originally Posted by gregbradley
I also am interested in the APM 12.5mm Hi FW as it appears to be a clone of the Docter 12.5 which seems to be a legendary eyepiece.
Greg.
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The APM 12.5mm has one more element than the Docter, a slightly larger field stop, a millimeter less eye relief, so not exactly a clone.
That being said, distortion characteristics are almost the same, with angular magnification distortion (rolling ball or globe distortion) predominating, unlike most astronomical eyepieces. It is usable with glasses.
It is quite sharp but also has a bit of edge of field brightening (EOFB).
No noticeable spherical aberration of the exit pupil (SAEP).