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Originally Posted by dcnicholls
One question arises: since astigmatism seems to swamp coma for eyepieces below a certin quality, at what point on the quality curve does a paracorr start to make a visible difference? Anything better than el-cheapo Chinese eyepieces? Something like the Meade 5000 series? Or only for things like Naglers and top Pentaxes? Comments aprpeciated.
2. Floaters: Don, if you find a way to deal with them, please post here!! My eyes are a zoo 
DN |
DN
Here's some info on floaters:
http://www.eyefloaters.com/
Note that laser fixes for floaters is not yet considered a standard procedure. But, short of replacing the fluid in the eye, this remains the only current cure.
As for eyepieces, if astigmatism swamps all other aberrations (say, using a Chinese widefield at f/4.5, for example), then eliminating coma will only make a minor improvement. But if the eyepiece is decent (like the new Baader Hyperion or the Orion version), then it can be valuable to add a coma corrector. A few posters on Cloudy Nights have done just that and been pleasantly surprised at which eyepieces were improved and which weren't. It's possible an eyepiece that appears unsalvageable without coma correction may become quite tolerable with it. I think you never know until you try it. But, as you say, the better eyepieces that have little or no inherent astigmatism do seem to be the ones that are made nearly perfect by simply correcting coma.