Quote:
Originally Posted by mandragara
Thanks for the extra info guys. I like the grounded nature of these replies, so many of the CN replies seem to encourage people to buy things for the sake of it.
I'm going to wait for a night of good seeing over Sydney and then tease out what this optical artifact is.
Some research shows it might be astigmatism. If so, given the effect is distributed radially about the center of the field of view, that indicates that it would be eyepiece astigmatism. Yet I perceive it in my Tele Vue eyepieces, which should be well corrected for that.
So another culprit would be field curvature, which would explain the radial distribution and the abberations presence in both. I wear glasses but do not observe with them on, as I only suffer from spherical abberation (no astigmatism) and can tune the focus wheel to compensate for it. However, I might be lacking the ability to focus on the stars at the centre and edge of the FOV at the same time.
So it's not an easy diagnosis, but my suspicions are now more directed at field curvature than coma. This is going to take some detective work, if it is field curvature I should be able to tune the focuser to get the edge stars sharp and the centre of the FOV blurry.
I found this website handy by the way: http://umich.edu/~lowbrows/reflectio...scobel.27.html
Cheers,
Richard |
I too wear glasses but, detest observing with them on. I do actually suffer from astigmatism in one eye but, it doesn't seem to effect my viewing enough to bother me.. well, I don't notice anyways...
Might be worthwhile exercise observing with & without your glasses to see if the abberation is in fact.. your eyes... try each eye, with & without glasses to see if there is any improvement.. you might be surprised...
I find I can extract more detail using my right eye to observe Jupiter... whereas, I naturally use my left eye for observing, shooting, etc.. but, I tried my right eye on Jupiter one night & found I saw more detail... or at least, thought I did...
I own a number of ES 82* EPs & have no issues with them in any of my scopes, certainly nothing like the image you posted. Sure, there is probably some minor aberration right out on edge of fov but, I can't say I notice it plus.. I can't say I spend a great deal of time observing right out on edge of fov anyways. Don't own the 68* series but, have Vixen LVWs which are 65* afov & they are absolutely pin point to the edge in every scope I own...
Can't speak definitively for TV's as I don't own any... but, at the risk of being branded a heretic... perhaps they may not be as perfect or 'well corrected' as everyone makes them out to be... Also, I'll add that all our eyes are different so.. what seems perfect to one set of eyes may not be all that perfect to another set...
My suggestions FWIW are, have another look at your collimation perhaps revisit your routine using the astrobaby guide to see if your laser might be misleading you... check mirror clips, etc.. in case they've been over tightened & pinched the optics perhaps.. & try with & without glasses to see if any change in your view...
Certainly no point in spending money, rather large sum for a decent coma corrector if it doesn't actually improve your image.. I think you have a few things to check before splashing any cash...
Another thing to try perhaps is to see if you can borrow any eyepieces from a friend.. see if the problem persists.. even try some minimalist glass in the form of an ortho... if the problem persists no matter the eyepiece chosen, that would suggest the problem lies within the scope or your eyes rather than eyepieces..
Good luck with finding the source of your problem, please keep us posted on how you go... your troubleshooting could be very informative to others...