The Celestron Ultima LX line is designed for SCT's and Maks. They are not a good optical match with Newtonians. These in SCT's and Maks are excellent - I have the 8mm, and until recently the 13mm, and love/loved them both in my C8. BUT, put them in a Newtonian, and the image is terrible. Nothing wrong with the eyepieces. Nothing at all.
One aspect of scopes and eyepieces that is not understood well enough is that scopes and eyepieces actually need to be matched. This matching comes firstly from the 'focal plane' that different scope designs ( Newtonian, refractor, SCT, Mak, etc) is not a flat one. Newtonains produce a concave focal plane. Refractors, SCT's, Mak's, produce a convex focal plane. Eyepieces are then designed primarily to perform best for a given scope focal plane shape. Add further complications of big variations in f/ratio, radius of focal length, etc, in scopes, and then the built in corrections in different eyepiece designs, and the matching of eyepiece to scope becomes a very complex and difficult one.
There are very few entire lines of eyepieces that perform really well across all scope designs. Even in these lines, there are small variations in performance quality within the individual focal lengths. It is not plausible to expect all focal lengths to perform equally well - there are just too many lens variations to give different focal lengths, so it is a given that each focal length will handle different focal plane shapes to different quality capacities. Even within some very high end eyepiece lines there can be huge performance differences within the different focal lengths. It is unfortunate though that it is left upto individual consumer to inform themselves as to what eyepiece best suits their individual scopes. And keep in mind that within a whole line, there may be only ONE individual focal length that may actually suit a specific scope design!
For this reason, in my own eyepiece kit you will find a variety of brands, models and focal lengths that suit the scopes that I have.
Eyepieces that DON'T suit Newtonians:
Baader Hyperion, Orion Stratus, Celeston Duo, Saxon Superwide - exact same eyepiece design! The one exception here is the 5mm. The 5mm is actually a very good optical match. It is the only Hyperion that is in my kit. The Hyperion and its clones are designed for SCTs and Maks.
Celestron Ulitma LX. Similar to the above, but there are some optical design differences. Great in SCT's and Maks. Disaster in Newts.
Celestron Luminos.
Eyepieces that ARE a good match with Newts:
Plossls - very old eyepiece design that is very forgiving in most scope designs. They perform best in slower Newts, but still throw up a good image in fast Newts. Main problem though with plossls is the shorter the focal length, the smaller the eye lens, and the closer and closer you need to put your eye to the eye lens to see into it. These are very cheap to produce which is why they are the most common eyepiece design you will find included with half decent scopes. There are newer designs that also utilise newer glass types that easily out perform plossls, have a wider AFOV, and are only a little more expensive than plossls,
Explore Scientific 82 deg and 100 deg - These two lines are designed for fast Newtonians, and have a considerable degree of built in coma correction in them. This is essential as the faster the focal ratio, the stronger the coma, so these eyepieces need to be able to deal with this. A coma corrector performs very well with these to give sharp stars across the whole FOV. Coma correctors are not essential to use - I don't use one as the way I use my eyepieces I just don't get a benefit from them.
TMB Planetary type II - FANTASTIC short focal length line, and cheap. The 6mm is the weakest and should be avoided. This line is cloned by just about every brand of eyepiece, but they are all essentially the same eyepiece as they are inexpensive to produce so there is no advantage in changing optical components. These all have the same nice big eye lens, from the longest to the shortest, and all have the same long eye relief.
Vixen LVW - flaming brilliant eyepieces. These are one of the very few entire lineup of eyepieces that perform really well in all scope designs. Yes there are some individual variations within the individual focal lengths, but these are not too significant.
Tel Vue Ethos, Panoptics and Nagler. Excellent high end pieces.
There are others that are good and poor in Newts, and I'm sure other folks will add their experiences to this.
Cheers,
Mental.