Quote:
Originally Posted by Greenswale
Do I really need to try and find a Pentax XO5mm for planetary and double star work in a 120mm APO? Perhaps there is a viable alternative?
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Hi Wren,
The 5mm XO is a really good eyepiece optically, one of the very best. It's eye relief is very short and it isn't a comfortable eye piece to use for long periods IMO. I find that I can see just as much observing with an eyepiece like a 5mm Pentax XW because I am a lot more comfortable and relaxed, whereas observing with the 5mm Pentax XO is an effort, particularly for longer periods. 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.
I would rather be comfortable and relaxed with good detail, than straining to use the eyepiece, notwithstanding it may show a fraction more. The way I look at it is that a 5mm Pentax XW in my 10" or 14" Newtonians is going to show me a heck of a lot more than a 5mm Pentax XO in a 120mm APO, so I am not missing anything compared to owners of 5mm XO's and the like.
Cheers,
John B