The Baader Hyperion line was designed for refractors, SCTs and Maks.
Focal ratio means nothing if the scope design is not taken into consideration. An f/5 Newt IS NOT the same focal plane shape as an f/5 refractor. One is concave (Newt) and the other convex (fracs (as do SCTs & Maks)). How anyone can say that an f/5 Newt is the same as an f/5 refractor? Somehow it is mostly the visual types that make this mistake. AP types understand that field flatteners and coma correctors must be used, and that the two are not interchangeable between scope types - you cannot use a field flattener in a Newt and you cannot use a coma corrector in a frac. There's a reason for this. Yet this escapes us visual types... It was something I had to learn too.
Eyepieces are first designed with a particular focal plane shape in mind. And for that matter, it is much more difficult to design a whole EP line for Newts than for refractors, and consequently much more expensive to manufacture and buy.
However, contemporary eyepiece designs being what they are, while a particular line may be primarily for say refractors, it does not mean that all individual focal lengths from a given line will perform poorly in Newts. Instead it is often the case that from a given line there may be one, two or three individual focal lengths that may perform blooming well in Newts. Not necessarily "perfectly", but bloody good all the same.
To come up with a whole line that performs really well across both Newts and refractors is quite exceptional!
And there will still be some performance difference, small in most instances, even as eye strain, but there is no free lunch here either.
With the Hyperion line, the 5mm is the only individual focal length that performs really well in Newts. Joe mentioned using a coma corrector with it at f/4, but really not necessary, and certainly not with slower Newts.
All the other focal lengths in Newts will show a variety of aberrations, some more obvious than others, and also influenced by f/ratio. Astigmatism on the most part, field curvature as another. It does not mean you can't use say a 24mm Hyperion in a Newt - much of it will come down to personal preference. For some people what aberrations can be seen won't be a problem, for others these will be intolerable. Understand this and it may allow you to purchase a particular individual eyepiece that performs really well in both your Newts as your refractors and not have to shell out the big bucks for another eyepiece. "Cherrypick" if you will.
The Hyperion line has a special place in my heart though. It was with this line that I came to understand how eyepiece design is married to scope design and how they may or may not work, AND how individual focal lengths should not be used to cast judgement across an entire line as being "rubbish". When I bought the Hyperions I did not understand this, and bought them to use in my f/4.5 Newt, only to be disappointed. However, the 5mm was excellent in this same scope! Why? I asked myself. It was a mate, Wavytone, who suggested I try these EPs in a refractor, and PRESTO! They all did a mighty fine job in fracs! As at the time I mainly used Newts I sold all my Hyperions except for the 5mm. These days I use fracs, Newts and Maks. The Hyperions are just fine in fracs, Maks and SCTs (all these three having convex focal planes).
The Morpheus line is a totally different beast. It is a rare line that performs well in all scope types regardless focal plane shape. It is unfair to compare the performance of the Morpheus with that of the Hyperion. Totally different designs created under totally different criteria.
