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As an Abbe-Orthoscopic design, their eye relief is ~80% of their FL, which is probably a bit better than a standard plossl. The much sought-after (and way more expensive!!!) Zeiss Abbe-Orthos have similar eye-relief. I have the 18mm (ER 15.2mm) and the 25mm (ER 22.2mm). (The 4mm version has ER of 3.4mm...) They give excellent sharpness, contrast and brightness, but have only a 42-degree AFOV. The 25mm in particular is one of my favourite eyepieces; it has amazing clarity.
I find they compare extremely well with my 18mm Radian and 27mm Panoptic respectively: in fact they are possibly a bit brighter and offer better contrast. If you want to closely examine an object and get the maximum contrast for fine detail they are excellent, but they are not for those who want to enjoy a broader view.
I think you will find that most short FL eyepieces with longer ER (eg: Orion "edge-on planetaries" and other re-branded Long Perng) have in-built barlows, so extra glass and therefore less light through-put.
- Dean
Last edited by SkyWatch; 07-01-2021 at 11:38 PM.
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