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How to get rid of Coma..


mdstuart

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So I have an F5 Skywatcher, A lovely new 30mm 2 inch GSO lens. Great views in the centre of the field but coma at the edges.

What should I get to correct this visually. (other than a Nagler Teleview £200 eyepiece with dozens of elements)...

Any views would be helpfull..

Also what next in the 2 inch line. Is it worth getting a 15mm 2 inch eyepiece or does everyone use 1.25 inch lenses other than for wide field low power use?

Mark

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I'd suggest an MPCC as well although I think that will improve rather than completely correct the issue. Short focal ratio newtonians (I think the 250PX is F/4.8 which is pretty short) do have coma but low cost widefield eyepieces also show astigmatism at short focal ratios which sometimes hides the coma or combines with it.

Re: your other question, I think most people use 1.25" eyepieces for medium to higher powers. I certainly do.

John

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Have to go with the MPCC suggestion as it's the scope that has the coma, not the eyepiece. I had a 2" GSO (Revalation) eyepiece and whilst it's a great eyepiece in terms of value, you won't get a flat, aberration-free view in a fast newtonian with it but the MPCC will help a fair bit.

Tony..

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Are you sure it's coma you're seeing? ie. stars look like little comets at the edge of FOV pointing towards the centre. Less than premium quality eyepieces have their own edge of field aberrations that will drown out any visible coma which is an optical aberration inherent in the mirror of a fast newtownian, not the eyepiece itself.

I don't know anything about a 30mm GSO but if it's a premium eyepiece with good edge of field correction then a Paracorr or MPCC may help. If not, then a coma corrector would probably do very little.

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Thanks for the advice. I will continue to test the new eyepeice. I quite fancy a 15mm 2 inch though at some point..

It is amazing to have a field of view so wide thought. I cn just get Vega and the double double in one view!

Mark

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