Quote:
Originally Posted by ausastronomer
There are several solutions to the problem and all of them have inherent issues.
1) Leave glasses on. The issue here is that you need to use long eye relief eyepieces to accomodate the glasses and take in the full field of view and also to avoid scratching your glasses and your eyepieces. I will expand further on this option below.
2) Use a Televue Dioptrix. I don't like this option. I do a lot of outreach work where other people share the view through my scope. No one else can use the eyepiece with the dioptrix fitted unless they have an identical astigmatism correction to me.
3) Use contact lenses. I have tried this option on and off over many years and it isn't the answer for me. The issue here is that contact lenses are weighted at the bottom of the lens to correctly orientate the lens on your eye and correct for your astigmatism. Unfortunately when you observe you often get your head on funny angles which means the contact lenses don't align correctly to the right position on your eye every time.
I have found over many years that using glasses combined with long eye relief eyepieces (16mm to 20mm) is the best way to go. The convenience here is that you never have to remove your glasses when you alternate between, eyepiece, star chart, laptop display, argo navis display and naked eye viewing of the sky. It also leaves both hands free all the time. This may not sound important but when you are up the ladder of a 25" or larger scope you want to hang on with at least one hand, while you adjust the focuser with the other. It is important when you get glasses for observing to get good quality ones with high grade anti reflective coatings. If your glasses do not have good anti reflective coatings you will get reflections back into the eyepiece from the glasses themselves and off your own eyeball. You will think you have "moths" flying around inside your eyepieces. Moreso, if you combine cheap poorly coated glasses with cheap poorly coated and internally baffled eyepieces.
I think I have covered most things. If not ask away. I have suffered astigmatism and observed with glasses for over 30 years and tried every available option known to modern (and ancient) science 
Cheers,
John B |
John,
Wow, thanks for the reply,
A good overview of everything!
I don't think I have much, if any, astigmatism.
There are a few online tests etc and my optometrist didn't find any
worth noting.
However when you say it shows itself as flares around stars and you
can't see stars as pinpoints, did you mean with the correct glasses
on for distance vision or with glasses off?
Up until my forties I could totally 'relax' my eyes and they would
focus stars as pinpoints. As if in a total rest state, my eyes focused
on infinity naturally.
When I hit forty I needed to apply a bit of noticeable effort to focus
the stars and if I 'relaxed' they would turn to a flare....like a dandelion
flare...equally flared in 360 degrees around the star.
Astigmatism shows as
unequal flaring around a pinpoint, because the eye
lens is not a perfect lens any more but 'pulled' out of shape.
At least thats my understanding of it.
When driving at night also, I could see a very distant pinpoint street lamp
as a set of beautiful diffration rings if I relaxed my distant vision back to
out of focus
If I had astigmatism, wouldn't the rings be distorted?
Now as for using eyepieces, you recommend the use of long eye relief
eyepieces and glasses on as your preference.
Obviously you need the glasses as you say, to correct for the astigmatism
component of your defect and leaving them off would introduce some
residual flaring even though you could focus and correct the myopic
component.
For me, I feel very uncomfortable having any gap (the gap that eyeglasses
cause) between the eye and the eyepiece.
I have had no exposure to high end eyepieces like you have and so
probably can't comment about their benefits WRT eyeglasses and
eye relief.
Also I don't like the way that gap introduces secondary reflections from
external sources (dome LEDS etc) buggering up the contrast of the
view from the eyepiece.
When I have friends over of varying ages, and kids for example, with
perfect vision, the setting that I leave the eyepiece at (corrected for
myopia and no glasses left on) is still in focus for them too.
I sometimes think they are just being polite and then dial in a bit of
out-of-focus and then they say "hey no, now it's blurry"
Once again, thanks John for the insight,
regards,
Steve B.