[mental4astro (Alexander)]

Hi Rod,

There's a couple of things to consider with coma correctors. They will help deal with coma but not astigmatism in eyepieces. In astigmatic EPs, the abberation will remain unaltered as this occurs post corrector. They also won't correct for abberations like pincushion.

The other thing is you WILL loose light. While coatings & lenses in correctors have improved, you will always loose light.

In the end the choice is yours.

As a user of f/4 & f/4.5 Newtonians, I did give coma correctors a go, but gave them up because of this last point. I'm happy to deal with the small abberation that coma really is, even with my 36mm EP in my 8" f/4 Newt. I've been slowly changing over my EPs to ones that have astigmatism & other abberations better controlled. For some abberations it is also a matter of a mismatch between the EP & the scope as in pincushion.

For me, coma is a very subtle thing. I understand why it happens, and with all other abberations controlled I'm prepared to live with it in my low power EPs. It only happens at the edge, which is an area that serious observing is NOT done - you move the scope for this, even if you are using a corrector.

There is one last thing. Coma does become more pronounced when ultra wide angle EPs are used. Comparing the edge of two EPs of the same focal length, one 68* AFOV & the other 100*, the latter will show more the effects. Having said that, in my 36mm 72* Aspheric Hyperion, coma is still very, very subtle along the edge in my 8" f/4. Astigmatism, while not totally eliminated from this EP/scope combination, is still more pronounced than coma & it is very well controlled in this extreme combination.

Please consider.

Mental.