Quote:
Originally Posted by Greenswale
I still have one excellent eyeball and wish to take advantage of it while it lasts! Tight eye relief is not an issue, my 4mm has a quoted 3.4mm eye relief, thus the thought of a the XO.
Summarising, advice given and my preference suggests a minimal glass, fixed focal length type eyepiece. So, what eyepiece offers direct competition to an XO?
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Quote:
Originally Posted by ausastronomer
If you're striving for the very best then a top class simple eyepiece like the 5mm Pentax XO, or TMB Supermono, or Astrophysics SPL, or Zeiss Abbe will give up a fraction more in moments of steady seeing than a high class long eye relief widefield, but there isn't a huge difference either.
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Hi Wren
As Allan mentioned, at "exactly 5mm" your choices are limited to the Pentax XO, Astrophysics SPL or the TMB Supermono. The 30 degree AFOV of the Supermonos doesn't work for me and neither does their poor off axis performance in faster telescopes. The 5mm Astrophysics SPL is extremely hard to obtain, so as Allan mentioned you're back to where you started and the 5mm Pentax XO is likely to be your best option.
If you're striving for the very best optically and you move away from "exactly 5mm" your options expand to include the 4mm and 6mm Zeiss Abbes (version 1 or Version 2 are both exceptional) and the 3.8mm Pentax XP. The 3.8mm Pentax XP has a .965" barrell and about 2.8mm of eye relief, but it's an exceptional performer optically. It is normally sourced with the adapter supplied as well, either in Aluminium or Delrin. The 4mm and 6mm Zeiss Abbe's and the 3.8mm Pentax XP would likely be marginally better performers optically, than whatever else you might currently be using at these focal lengths.
Cheers
John B