Telescope Reviews: 80mm Triplet with Perfect Edge Stars... possible?

Field curvature is almost guarenteed to be the issue with this scope when using modern wide field eyepeices.

Daytime testing may show the 31mm Nagler to look much sharper than another eyepecie, but the 31mm Nagler may still not present pinpoint stars at the edge of the field at night.

A point source is one of the most difficult targets you can use when checking for off axis abberations. It is without mercy.

So, don't be surprised if you still can't get the view to be pinpoints all the way across at night.

There is also this. Someone not so long ago in this exact same forum was concerned that his new fast APO was not giving very sharp images. These fast scopes, when used with eyepeices like a 31mm Nagler, will start to reveal astigmatism in the observer's eye for most observers. It becomes very difficult to keep the field sharp because so much of your eye pupil is being utilized that any abberations in your eye lens will start to show. When the exit pupil is smaller than about 2 or 3 millimeters, even observers with astigmatism may not need their glasses, but when the exit pupil is 6mm or 7mm, even people that don't have astigmatism bad enough to require glasses may start to see stars less sharply.

I could not even keep the entire field of a 102mm f/9 ED scope all in focus when using a 31mm Nagler. Nor could I keep the entire field in a Televue 101 perfectly focused. Part of it was my eye, part of it was field curvature from the scopes.

For the same size true field, it is easier to keep the field all in focus by using a 68 degree afov eyepiece. For example, a 22mm Nagler and a 27mm Pan give about the same size true field, but if you are having trouble keeping the entire field in focus, it will be easier to do with the 27mm Pan. So, for the same size true field of view, a longer focal lenght eyepiece is the best way to reduce the effects of field curvature of the scope. Of course you give up some of the "Spacewalk" offered by the bigger apparent field of the Nagler, so you have to ask yourself which is more important, the wider apparent field, or a field that is more pinpoint all the way across..

I love pinpoint fields. I personally would rather use a Panoptic given the same size true field than a Nagler so I can keep the field as perfectly presented as possible. That to me gives more of a spacewalk experience than looking at a field that is populated with lots of abberated stars.

We each make our choices though, and many people only care about the center of the field.

You appear to be growing more discerning with respect to off axis performacne, and you may indeed find that if you want both Nagler/Ethos views and pinpoint stars to the edge, you may need to go to a different scope, or ad a flattner to your current scope.