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Originally Posted by Rodstar
What's the focal ratio of your truss dob, Scott? Do you experience much/any coma?
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It is an F5 (I also have an F6)...I do not find coma in my scope particularly noticable (to me) and it is not bothersome to my eyes but would suggest that I am not the "pickiest" or most experienced observer (still comparatively green in the observing department relative to other posters in this thread) and I think I have a pretty good set of corrected eyepieces (at least IMHO) Naglers, Pentaxs and one Panoptic with a couple TV plossls and a Powermate...I am not saying coma does not exist in my scope, I am saying that my veiwing habits and experience are such that it does not bother me (or hasn't yet but having participated in this thread I'll probably be driven crazy the next time I am out with my scope looking for the coma...talk about being influenced and poisoned by more information).
I have never used a Paracorr in my scope but have often wondered what kind of improvement I might find. I have no doubt that if I looked closely I would see an improvement but have struggled with the justification of buying/owning one to myself without the prior use of one. I suspect/speculate that the benefit would be two fold one in reduction of coma present but also the slight "barlow effect" too...but at a cost that I am not sure I am as yet prepared to pay based on use and experience...
From all I've read (not yet experienced) I'm not concerned by loss of light...I am more concerned with added weight and the likely need to rebalance things...not a real objection I know but it is in my mental decision mix.
I am interested in trying one and most likely will own one someday...not necessarily soon (or necessarily with this scope) but it is on my longer term "wish list".
Having said all of that, if I was buying/building a new big fast dob I'd get one and have it built/counterweighted to carry a Paracorr and the bigger Nagler/Pentax eyepieces standard (leaving the Paracorr in all of the time)...the incremental additional cost is small relative to the cost of the new optical system and my belief is that in scopes faster than F5 it probably pays for itself pretty quickly in noticable improvements for a discriminating eye (and if I spent big bucks on a new scope I'd be much more discriminating)...
As was noted in this thread earlier, if you are going to all of the troube to get a high end (read expensive mirror) you might as well get the equipment to let the thing work at it's peak...I mean, what good is owning a high performance race car if you are going to put cheap tires (tyres) on it and use low octane fuel?
I am looking forward to getting the chance to look through your new scope (and Paracorr)
Cheers!