[mental4astro (Alexander)]

Hi Knigtrider,

First, aberrations. Coma is an aberration ONLY seen in reflectors. Many people say they see coma in refractors, they are mistaken. They would be seeing other aberrations, namely spherical aberration and field curvature.

Coma appears as little comet tails that comes off stars, appearing to radiate from the centre. Coma is most apparent at low power and towards the edge of the field of view. Coma IS NOT a flaw in either scope or eyepiece. It is a phenomenon of reflectors and EPs. The faster the f/ratio of the Newt, in this case, the more evident coma will appear. EP design helps a lot in dealing with coma, but these Newt specific EPs are more expensive as it is more difficult to design and manufacture EPs for Newts than other scope designs. Also, the higher you go in magnfication, the less and less coma is apparent. But in your 10" dob, coma is not a significant issue.

Astigmatism is a symptom of an optical mismatch between scope and EP. It appears as little "seagulls" coming of stars, co-centric to the centre, and most evident towards the edge of the field of view. EPs designed specifically for Newts will display NO astigmatism. They may show a little coma, but astigmatism is eliminated. You have seen these seagulls in your 30mm Superview. Maybe you had noticed a "distortion", but that is astigmatism.

Eyepieces do not perform the same regardless of the scope they are used in. EPs are designed first to work with a specific focal plane shape, convex (refractors, SCT's and Maks) or concave (Newts). EPs for a convex focal plane are much easier to design for and cheaper to manufacture. This is why TV's and some Explore Scientific EPs are so pricey. Understand this concept of optical matching an EP to a scope design, and much of the issues written about in reviews begins to make sense and that there is a lot of ignorance about EPs towards scopes. I used to also think "this is an eyepiece, this is a scope, it will work". It is not as simple as this. You've already had an insight that things are not quite like this because of what you are seeing with your 30mm SuperView.

Eyepieces.

When looking for EPs for a Newt, if $$$ are a concern that makes Newt specific EPs too expensive, look for EPs that then best control astigmatism. And yes, it is possible to find EPs that are not Newt specific that actually show no astigmatism in Newts.

DON'T make the mistake of dismissing an entire line/model of eyepiece based solely on a review of one single focal length EP out of an entire line/model. The complex nature of EP design means that while most EPs are not designed for Newts, there can be individual focal lengths from a given line that will actually do a bloody good job in Newts, showing anything from little astigmatism to none at all. If you are prepared to accept just the smallest amount of astigmatism, then a whole lot of really good and inexpensive EPs will come into play as excellent Newt eyepieces.

There's another thing about 1.25" eyepieces, well really all eyepieces regardless of the barrel size. They will only show a maximum amount of sky, and all due to the size of the barrel. Think of it this way, you have two straws, both the same length, but the difference is their diameter, one is wider than the other. You look through each, and which will show a larger amount of the background? The wider one. So you won't find a 30mm 100° 1.25" eyepiece, because the barrel just won't allow it. For that matter you also won't find a 30mm 100° 2" eyepiece either. The longest focal length EP that will give a 100° AFOV in the 2" format is 21mm, and much shorter again for a 1.25" EP.

From your post, I guess you are reacting to the astigmatism that you see through your scope with the 30mm Superview.

Some EP suggestions.

The EP Jeremey kindly posted about will show as much astigmatism in your dob as the 30mm SuperView. It won't show an improvement. You may not be too happy with it if you find the 30mm difficult.

One 23mm 82° that is really blooming good in Newts is the 23mm Celestron Axiom LX. Shows just the smallest amount of astigmatism at the very, very edge of the field of view at f/4.5, and you really need to go hunting for it, & at f/5 even less. It is no longer available new, only second hand. I absolutely loved mine. DO NOT confuse it with the 23mm Celestro Luminos - totally different internal designs and they come from different manufacturers too. You can post an ad in the Wanted forum for this 23mm Celestron Axiom LX.

Of the ones that you mention in your post, I do not have experience with any of these. HOWEVER, knowing now how to recognize astigmatism, when you read through reviews, use this knowledge to help you figure out if the reviewer is seeing any astigmatism IN THAT SPECIFIC focal length, and how much they see. Also look at what scope types the EP the review is used in - if you are looking for an EP for a Newt, tghe review NEEDS to mention the eyepiece being used in a Newt. Do not base your EP decision making on reviews where the EP has not been used in Newts. I did that mistake early on and it cost me a lot of money to learn this lesson. I know better today and I want you to learn it now before you repeat my mistake.

Most people do not understand optical matching between EP and scope, nor the complex nature of contemporary EP design and will dismiss an entire line based on just one single focal length from a given line/model. You can now use the above knowledge to start searching for those Gems of EPs that are both inexpensive and good performers in Newts. It is something I've been doing for a very long time, and slowly been building a bank of such info.

Remember, READ about individual focal lengths in reviews. Do not base your purchasing decisions on reviews about OTHER focal lengths. This will give you the info you need.

Alex.