Hi John,
A couple of things before I suggest an EP or two.
* First is the size of the exit pupil of this range of EP focal length will exceed 7mm. This will mean that not all the light coming out from the field lens will enter through your fully dilated pupil. If you're ok with this, then no problem. I don't mind myself & regularly employ large exit pupils as I still enjoy the view. Heck, I even use a 65mm EP in my f/4.5 17.5" dob!
* the other is the abberations that become visible in this fast scope/long EP combination. Astigmatism being the worst offender. It shows as a seagull effect coming off the stars along the FOV. The worst offending EPs have this start further in closer to the centre. Other EPs show very, very little, which is excellent, others show none.
Coma is a function of a fast Newtonian, and it can be corrected for by using a coma corrector between the EP & focuser. Some folks swear by them, I rather not use one as I don't see the nett gain being worth the loss of light from using one. Coma is also a very soft & relatively minor phenomenon/abberation really. Astigmatism is much worse. BUT, the wider the AFOV an EP has, the more significant coma becomes. Eg, two EPs, same focal length, one 68*, the other 82*, the former will show less coma at the edge than the latter.
Now, EPs. This has been my mission in this hobby to find the real gems that don't cost the Earth. Just note that the following recommendations are for ~68* AFOV EPs, & noted cheapest to most expensive.
- GSO Superviews, 42mm & 50mm, are excellent for bugger all price. BUT, the are astigmatic in fast Newts, but less so than other more expensive EPs. Great first 2" EPs, & excellent for using at star parties as you won't mind them getting cruddy & cleaning them regularly.
- Meade Series 5000 SWA, 34mm & 40mm. Though now discontinued so only 2nd hand, are exquisite in fast Newts. Note, these are HUGE eyepieces, the 34mm is 785g (I've got one), & the 40mm is over 1kg.
- Explore Scientific 68's, 34mm & 40mm. These are the exact same EPs as the above Meades.
- Baader Hyperion Aspheric 36mm. Shows a bees willy more astigmatism than the above 34mm Meade, but still a great performer in my f/4 dob. In your f/5 you may even see none. Not a heavy EP either (got one too).
- TV Panoptics. I'm only going by Reviews I've read on these, but by all accounts excellent EPs. $$$ though, even second hand.
There are others that other people may like to mention.
Take your pick
Mental
John , have you seen the 55mm TV plossel in the classifieds? its now only $180 , great eyepiece for your dob .
and it cost me $79 more than I wanted to pay ($279.00)
