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Orthoscopic Eyepieces
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These Abbe-type orthoscopic oculars are good value for anyone seeking a high-contrast planetary eyepiece. These orthoscopic eyepieces are a four-lens design,  and feature excellent contrast, flat fields, superior colour correction, and freedom from scattered light.
The chrome-plated brass barrels with aluminium top design includes filter threads.  For image definition, contrast and light transmission, the eye lens of each eyepiece is multicoated, all other surfaces are magnesium flouride coated.
The slight drawback is that they offer smaller fields of view compared to the Plossl design equivalents.
ore1.jpg
Generally available in focal lengths: 4mm, 5mm, 6mm, 7mm, 9mm, 12.5mm, 18mm, 25mm

These popular eyepieces for astronomical observing, offer very wide, flat fields, excellent spherical and chromatic corrections, greater eye relief than Kellners, and freedom from scattered light. With four-element design, coated lenses, mounted in standard 1-1/4" O.D. chrome-plated brass barrels with aluminium tops.

£64.64

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Orthoscopic Eyepiece Specifications
FOCAL LENGTH4mm5mm TWP-IF/CF6mm WP-IF/CF7mm9mm12.5mm18mm25mm
APPARENT FIELD OF VIEW41°43°43°42°42°44°46°47°
EYE LENS OD4mm4.5mm5.8mm6.5mm8.3mm11mm17mm21mm
EYE RELIEF3.5mm4.0mm4.8mm5.6mm7.2mm10.0mm14.4mm20.0mm
COATINGSMulti-Coated Eye Lens; MgF2 on all other surfacesMulti-Coated Eye Lens; MgF2 on all other surfacesMulti-Coated Eye Lens; MgF2 on all other surfacesMulti-Coated Eye Lens; MgF2 on all other surfacesMulti-Coated Eye Lens; MgF2 on all other surfacesMulti-Coated Eye Lens; MgF2 on all other surfacesMulti-Coated Eye Lens; MgF2 on all other surfacesMulti-Coated Eye Lens; MgF2 on all other surfaces
BLACKENED LENS EDGESYesYesYesYesYesYesYesYes
WEIGHT80g85g87g90g92g96g97g100g
1.25" FILTER THREADSYesYesYesYesYesYesYesYes
COMPATIBLE WITH BINOCULAR TELESCOPESNo (focal length too short)No (focal length too short)No (focal length too short)No (focal length too short)YesYesYesYes

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Orthoscopic lens layout:
Orthoscopic eyepieces consist of a cemented triplet lens group and a separate lens. Cementing three lenses requires sophisticated machinery and a lot of experience, but the result is a superb image sharpness on the optical axis - better than in ordinary Plossls or typical wide angle eyepieces.
Only eyepieces with this precise lens layout are considered Orthoscopic eyepieces.
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Ed ~ as noted before, the smaller field of view is a drawback to an otherwise excellent eyepiece design, (but an aspect generally considered irrelevant when low focal length eyepieces are used for planetary or lunar observations).  A typical 1000mm long focal length telescope when used with a 12.5mm eyepiece will  give a magnification of 80x; and the 25mm eyepiece, 40x magnification. These would be excellent sizes for planetary and lunar work.  However, short focal length telescope owners are best to opt for wider field of view eyepiece designs if considering Orthoscopic eyepieces greater than 12.5mm. The advantages of the Orthoscopic are somewhat lessened by the wide angle rich field eyepiece designs, (namely the relatively inexpensive Possls).



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