The 7mm Pentax will give you 285 mag in your scope. So it will be of no use for DSO nebulas which are better viewed in the context of their surroundings.
As far as coma is concerned, your FL is very forgiving so you may find not much difference between say a Hyperion and the Pentax. Still, the Pentax according to what I have read is a very nice contrasty eyepiece; and considering what it costs it should be.
If you wish to own a premium eyepiece then i dont think you can go wrong with a Nagler or a Pentax. I have many Naglers and even though i am now into imaging and dont use them much, still I would like to keep them as one day i may need a decent eyepiece and the ones I have are very good and will still be just as good 10 years from now.
Maybe you should say what you wish to use the eyepiece for?
Hi
285x magnification is way too much for your scope on most nights, it will lead to frustration especially if your scope is not collimated properly. May I suggest something around 13-14mm which will give you a lot more usage and much nicer views. I use Pentax 14mm in this range but there are other good eyepieces like TV Nagler or Ethos, Vixen LWW....
As the others have started 7mm is a lot of magnification on an 8" SCT. I have a 7mm Burgess EP which I use on my ED80, I've tried it many times in my LX90 but have never found the conditions to be good enough. at that magnification. I find that my 13mm Baader hyperion, at around 150x magnification is the most used.
