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PaulM

Coma corrector : 350p skywatcher

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In lower magnification compared to my old 8" and 12" skywatcher dobs I'm noticing the focus is out around the edge of the eyepiece when I focus the central starts\objects in my 350p 14" dob so would a coma corrector address this issue if so are the below good options? 

If so I assume I can only use these with a 2" EP with these?

http://www.firstlightoptics.com/coma-correctors/baader-mpcc.html

http://www.firstlightoptics.com/coma-correctors/skywatcher-coma-corrector.html

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Looking at your eyepieces (assuming these are what you are using) you might be seeing astigmatism rather than coma. Coma will also be there but eyepieces that stuggle with the F/4.5 focal ratio will show astigmatism in the outer field of view which tends to mask the coma and/or combine with it.

A coma corrector will tighten up edge of field views by controlling the coma but won't address eyepiece astigmatism if that is the primary cause of what you are seeing. Some more info here on these issues to help you decide what the issue is:

http://umich.edu/~lowbrows/reflections/2007/dscobel.27.html

 

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Posted (edited)

 

 

Hello

Unfortunately with the faster focal ration scope. Eyepiece selection becomes more critical. I take it your 8" and 12 " dobs handled your previous eyepieces fine as they were a slower focal ratio. But now with the 14" at a faster ratio, then eyepiece choice becomes more critical. Therefore unfortunately that usually means upgrading the eyepieces to cope with the faster scope and to get the best out of your faster ratio 14" dob. Gives you an excuse to buy more eyepiece's😱

 

 

 

Edited by Timebandit
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17 minutes ago, Timebandit said:

 

 

..... Gives you an excuse to buy more eyepiece's😱

 

 

 

...... and then a coma corrector because the better corrected eyepieces will allow the coma that the scope produces to be seen more readily :rolleyes2:

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The coma correctors you listed are not general purpose visual correctors.  The only three general purpose ones that I'm aware of are the TV Paracorr, the ES HR CC, and the GSO/Revelation CC.  The GSO version is the cheapest and easiest to use because it has a 20mm wide sweet spot.  Unfortunately, it isn't plug and play straight out of the box.  It requires adding a 25mm extension between the optics nose piece and the eyepiece holder.  It will flatten the field as well.  It also adds only 10% magnification and requires about 10mm to 15mm of infocus.

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