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Old 18-09-2019, 06:51 AM
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mental4astro (Alexander)
kids+wife+scopes=happyman

mental4astro is offline
 
Join Date: Jun 2008
Location: sydney, australia
Posts: 4,633
The reason why I want a review of an EP without a coma corrector in place is because it helps me evaluate the design characteristics of a given EP to gauge how well matched it is for a Newtonian.

As an example, take a 13mm Nagler Type 6 & a 14mm Vixen SSW. In an f/4 Newt, the Nagler is just about perfect along the edge. I actually don't need a coma corrector here as the image quality along the edge is so good and I don't do any serious observing along the edge - no one does. But the SSW in a Newt is no where as good, displaying much more significant coma effects and some astigmatism.

Now in my 7" f/15 Intes Mak, the SSW has it all over the Nagler! The roles are reversed. The SSW is sharp across the FOV, and easy on the eye to use, and the astigmatism is gone - a better match with the Mak. Yet the image with the Nagler is not as sharp towards the edge, and I find eye placement is more tricky that with using it in a Newt.

Edge performance, and in particular the aberrations that are seen are indicators to the matching of the EP to the scope being used. If you have any doubts, you need to read the work on EP aberrations here, https://www.telescope-optics.net/eye...rrations_1.htm , which describes how scope design influences eyepiece performance and design.

The eyepieces in my kit I have collected according to how the perform in my various scopes, Newts, SCT's, Maks and refractors. MOST of my eyepieces are used either solely in either Newts (such as the 13mm Nagler) or the other three (such as the 14mm SSW). I have very few EPs that I use in all my scope types. I make my purchase decisions on actual performance, and certainly not on Brand popularity. However I do use other people's reviews on any given EP to help identify those key aberrations that demonstrates that EP's performance for a given scope design. This is why I find Bill's reviews invaluble as he makes a point of trying EPs in different scope designs, not just in one scope and f/ratio.

Alex.
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