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Originally Posted by mental4astro
Hi Knigtrider,
First, aberrations. Coma is an aberration ONLY seen in reflectors.
Alex.
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This is clearly incorrect. Several telescope designs have inherent coma, including Schmidt Cassegrains, Maksutov Cassegrains, Classical Cassegrains, Dall Kirkham and of course Newtonians.
In fact the inherent coma in the Schmidt Cassegrain design led to Meade releasing a modified design Schmidt Cassegrain which they incorrectly called a Ritchey Chretien and after a legal battle they changed the name of the new design to
ADVANCED COMA FREE telescope
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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.
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Again this is clearly incorrect and it is something you continually harp on and try to push across with zero substantiation.
The only Newtonian specific eyepiece that has ever been designed and built is the "Pretoria" eyepiece, which had an inbuilt coma corrector. This was sold by University Optics and Brandon (Vernonscope) in the 1980's. When Televue released the paracorr in about 1990 the Pretoria eyepiece died out because the paracorr could be used across multiple eyepieces and was more versatile, particularly when they subsequently released the tunable top version of the paracorr.
The facts are that the eyepieces which perform best in fast Newtonians are eyepiece like Naglers, Radians, Ethos and Delos made by Televue, Nikon NAV HW made by Nikon and a few others, none of which are made by companies that make Newtonian telescopes. It just so happens that the only telescopes Nikon and Televue produce are refractors. Do you seriously think that companies like Nikon and Televue are going to design an eyepiece to work well in Newtonian reflectors, but not work well in the telescopes they design and sell?
Fact is these eyepieces work equally well in both Newtonians and refractors and just about any other telescope design you care to drop them in.
Unfortunately Alex, to people new to astronomy, you sound like you know what you're talking about when it comes to optics. To people who have been around a while, it's pretty obvious that this isn't the case.
Cheers
John B