Well he did say that he wanted the maximum magnification of quality. The maximum recommended magnification of most any telescope is 2x per millimeter of aperture which suggests he would top out at 140X. It looks to me like the scope is a little less than f/13. So half the focal length in eyepiece focal length gives you an ideal eyepiece of 6.5 mm.
If you use a six or seven millimeter eyepiece on this scope the view will be dimming out and the jittery qualities for which these kinds of scopes are famous, due to their mounts, will be greatly exaggerated. I would suggest eight or nine millimeters as a more practical upper boundary for this telescope that would give a good view often whereas a 6 mm would give a good view only occasionally from time to time. That would be due to the seeing and also the jittery mount.
Even though the focal ratio is a little long, as it should be on an achromat, putting in an eyepiece that has 0.5 mm exit pupil will bring out the chromatic aberration.
If however the objective is lunar observing then a 6 mm is a good choice because it will allow you to get the high magnification lust out of your system.
Another argument for sticking to 1.5x per millimeter of aperture or thereabouts is that on a very small aperture instrument like this one will quickly encounter the airy disc limit where stars become plainly visible as fat discs, an optical artifact That has nothing to do with the quality of the scope but everything to do with its aperture.
As I recall Edmund optical makes a nice little 1.25-in 8 mm eyepiece for about 50 or 60 bucks. I think it would do the trick nicely. An XW or a delos would probably overwhelm the telescopes capacity for balance.
Edited by gnowellsct, 15 July 2020 - 03:04 PM.