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Yes Neil,
Those calculations are correct.
Some super wide EP's suffer from coma around the edges whereby the stars look smudged and develop tails.
Generally, you get what you pay for. A cheap super wide will probably be cheap performance, OK in the middle third (like a bulls eye) but rubbish around the edge. If you want super crisp stars right to the edge and massive wide field of view, then the ETHOS range from Televue are the way to go (no doubt there are other brands) but the trouble is, they cost more than some cheap telescopes (upwards of $600-900 EACH!!!)
Your best bet is to go for a 52 degrees Field of View (FOV) or a 68 deg FOV ED type eyepiece which are sub $60 depending on the brand. I have a few plossls, my Hyperion (second hand for $100), my ED 12.5mm - 68 deg and the first eyepiece I use when I unpack the scope, my 2" barrell 68 degree "wide field" Andrews brand 32mm, (very bad coma) and my Pentax XF 8.5mm ($230) which I use when I want some nice crisp close ups of planets like Jupiter without any false colour from barlows or powermates.
Its surprising just how satisfying my Skywatcher plossl's are.....considering they came with the scope. They perform quite well and the difference, whilst noticeable by me, is not something that can really justify the loading of $200 to buy say the Pentax, for a beginner.
I went a little "accessories crazy" early on, of which I am now cured, so trust me when I say a plossl is good value for money at this stage and well worth a look. Stay away from exotics and "super wides" until you can look through some in YOUR scope when at a star party or club event as only then you will be able to gauge whether the eyepiece of the future is worth it in your scope...
Hope this helps save you from sliding down the wallet busting path I almost fell down.
Cheers
Chris
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