I will give a run down on my EP's while they are sitting right in front of me.
Report using GS f5 12" Dobsonian.
Series 500 - 6.5mm: Straight tube without locking recess, Hard rubber eye cup, single light-blue coating, badly threaded tube inner.
In use: Will not focus to a crisp point, Flaring of bright objects, disastrous eye relief.
Views: Poor
Series 500 - 15mm: Straight tube without locking recess, Hard rubber eye cup, single green coating, badly threaded tube inner.
In use: Will not focus to a crisp point, Flaring of bright objects, bad eye relief. Mild to very noticable image distortion at edge of FOV.
Views: Mediocre
Series 500 - 25mm: Straight tube without locking recess, Hard rubber eye cup, single light-blue coating, badly threaded tube inner, handy rubber grip around body.
In use: Will not focus to a crisp point, Flaring of bright objects, reasonable eye relief. Mild to very noticable image distortion at edge of FOV.
Views: Mediocre
GS Plossl-9mm: Locking recess, soft fold-down rubber eye cup, aqua-blue & mid-green Multi-coating, finely machined tube inner thread,
In use: Good Focus, no flaring, reasonable eye relief, Mild to nil image distortion at edge of FOV.
Views: Pleasing. Very good.
GS 2" 30mm SuperView: Locking recess, soft fold-down rubber eye cup, light-green, violet & mid-green Multi-coating, finely machined tube inner thread, threaded section not painted black.
In use: Excellent Focus, no flaring, excellent eye relief, Seagull shaped distortions at edge of FOV until cool-down.
Views: Pleasing. Excellent Wide-field views.
This is a fair & reasonable report without extrematism.
