Russell,
A good mate of mine turned my attention to this aspect of matching optics. I was having a poor time with some eyepieces, and in speaking with Wavytone (here on IIS), he explained the importance of matching eyepieces with scopes.
Eyepieces have been designed for particular scopes since scopes started being described mathematically. Eyepieces are still designed this way. Unfortunately eyepiece producers fail to tell us this, and it is left up to us to figure out what is going on. The biggest problem this creates is when an eyepiece is reviewed, someone with eyepiece 'X' and puts it into scope 'Y', and the image is crap, then the reviewer dumps on eyepiece 'X'. The reality is eyepiece 'X' should have been used in scope 'Z'. Or, consumer 'A' puts eyepiece 'X' into scope 'Y' after reading a view where the eyepiece was used in scope 'Z', and ends up very disappointed and none the wiser as to why - this happened to me with the Hyperions.
A good reference to this is 'Telescope Optics'. It goes into depth on scope and eyepiece design:
http://www.willbell.com/tm/tm6.htm
Max,
The best way I can describe the reason for 1.25", 2" even 3", 4" and 4.5" eyepieces is with an example:
You have two straws, same length but one is wider than the other. When you look through each you see a wider field through the larger diameter straw. This is what a larger diameter barrel will give. The maximum true field of view will be greater with a 2" barrel than a 1.25".
You would have noticed that there are different Apparent Field of View (AFOV) values with eyepieces. These can be 52deg, 58deg, 68deg, 82deg, etc. Keeping in mind that there is a maximum amount of sky that a given size barrel will show, there is a maximum value of focal length that can give a given AFOV. The longest focal length that will give a 68deg AFOV in a 1.25" barrel is 24mm. In a 2" barrel this is 42mm. You just cannot get a 40mm 1.25" barrel with an AFOV of 82deg - it just can't be done. But there are 40mm eyepieces in 1.25" barrel. The thing is the AFOV of such eyepieces will be small, around 33deg.
That aberration that you've noticed in your Superview is seagull shaped, more than 'comet' shaped. Seagulls spread out in the same direction as the edge of the FOV. This is actually astigmatism in the eyepiece being shown by the optical design of the fast Newtonian. There will be a little 'comet' tail showing coming from the centre of the star between the 'seagull'. This is coma and is inherent to fast Newtonians. Astigmatism is one aberration that is shown with an eyepiece/scope optical mismatch.
The eyepieces I mentioned in my first post here have astigmatism much better controlled. Those noted as second tear start showing astigmatism - not a grotesque, but it is there along the edge of the FOV. This can be acceptable, but it ends up being a personal determination.
I can understand that the aberration that you see in your Superview is now challenging. If you are considering a better eyepiece, then those listed in my first post will better meet your requirement. Note that they will display coma if used neat in a Newtonian. Remember, coma is not an aberration, but a phenomenon inherent to Newtonians. This can be controlled by using a coma corrector. I'm happy to deal with a little coma as this is seen really only along the very edge of the FOV, and the way I use my gear, this is not a concern for me.
Note that what I've written here is not everything about eyepieces and scopes. Not by a long shot. It is just intended to start giving you some understanding that as "oils ain't oils", eyepieces ain't eyepieces and scopes ain't scopes.