Louis D

When star testing, astigmatism of the eyepiece will appear as a tangential line on one side of best focus and a radial line on the other side. At best focus, it will look like an enlarged star with the possibility of small spikes in both directions. You may also be dealing with field curvature. Focus on a star in the center and then move it to the edge. Does the tightness of the star image improve by refocusing? If so, you've got field curvature in either or both the telescope and eyepiece. Without a coma corrector, you could also be seeing coma from the mirror near the edge, though it isn't commonly seen in the narrow field of view eyepieces commonly packaged with telescopes. Generally, the eyepieces have enough aberrations of their own to overwhelm any mirror coma. What eyepieces came packaged with the scope? Are you wearing your new eyeglasses at the scope? To eliminate it being eye astigmatism, rotate your whole head around the eyepiece to see if the aberrations rotate with your eye. If they don't, they're in the eyepiece. If they do rotate, they're in your eye.

The 11mm DeLite would satisfy most of your requirements except for price. It's reportedly just a slight step down contrast wise from dedicated planetary eyepieces like the ZAOs and Pentax SMCs.

IIRC, in 1.25" mode, the 12mm NT4 required about 0.25" of IN focus relative to the shoulder, which was a pain in it's own right. That's the main reason I parfocalized it the way I did. When I use the GSO CC, everything needs to focus within about 5mm of the shoulder with the spacing I have to get 95%+ coma correction. The 12mm NT4 was so far off that uncorrected coma was plainly obvious without having to go searching for it. With parfocalization, coma is no longer noticeable. With the correction level I'm at with the GSO CC, eyepiece field curvature and residual edge astigmatism once again dominate the view, so I have never felt the need to get a Paracorr.

So pretty similar to the 12mm NT4 at 0.78" OUT. I had to add five 4mm thick O rings and a 20mm 2" extension ring to the 2" skirt to make it roughly parfocal with my other eyepieces that focus near the shoulder (reference surface). It was practically unusable otherwise because it required so many turns of the focuser to reach focus.

Try both metric and non-metric hex keys. I usually have to try both sets to find one that fits best.

The Celeston Luminos 10mm might also be worth a look as well.

Get a lower priced pair to start with to see if you even like using them. Some folks just don't get on well with binoviewers no matter the type or brand.

Stacking filters can lead to reflections bouncing back and forth between them causing ghost images of bright objects.

Glad it all worked out for you.

And, the smaller binoviewers have a shorter optical path due to using smaller prisms. Thus, there will be less vignetting if you shorten your truss poles to reach focus. If you go the route of the barlow to reach focus, I use the optical nosepiece from a 90s vintage Meade 140 2x barlow to good effect. It works out to a 3x boost. At that focal ratio, the 23mm Vite/Svbony aspheric 62 degree eyepieces work very well in them for maximum field viewing.

It's really exit pupil dependent, but even at smaller exit pupils, it's quite helpful on many emission nebula. Just start with large exit pupils and move your way up in power to see the effectiveness or lack thereof at smaller exit pupils. For galaxies and comets, there's no substitute for dark skies. Globular clusters need lots of magnification to resolve them. Many planetary nebula do fairly well at high power without filtration. Open clusters are of such high contrast that they are fine without filtration as well.

The human eye is pretty tolerant of edge vignetting. Even 50% is difficult to detect while looking in the center of a wide field eyepiece. Complete vignetting generally happens when the clear aperture of the binoviewer is significantly less than the field stop of the eyepieces because they're optically very close together. Try this calculator.

On many refractors, they won't slide in from the front because the tube widens just ahead of the focuser where the finder shoe is mounted, so there isn't enough clearance. Otherwise, I have no idea why they are designed that way.

Perhaps @jetstream could chime in here. I believe he observes from Canada which gets quite cold in the winter as well.

You keep all of your aperture but experience vignetting in the outer field by shortening your truss poles.

You didn't say if you wear eyeglasses and if so how strong your astigmatism is and if you have presbyopia. Do you need to refocus stars center to edge that you didn't use to have to? If so, you may be getting presbyopia and can no longer accommodate near/far focusing. If that is the case, you'll need to find flatter field scopes and eyepieces. Astigmatism in you eye would be visible center to edge and would be stronger in lower power eyepieces. This doesn't seem to be the case based on you description. The scintillation is worrisome. I recently had vitreous detachment diagnosed in my non-observing eye which causes random flashes in my vision. It has to be watched to make sure it doesn't lead to retinal detachment. Definitely get to an optometrist for a thorough eye exam.

Sounds good. Let us know how it works out. The GSO/Revelation 2" diagonal also uses an SCT thread. I screw an SCT threaded extension tube into it and then thread a TSFLAT2 field flattener onto the other end's M48 thread to flatten my refractors' fields.

Yes, you'll be moving your scope's mirror well away from its optimal design position to counteract the increased back focal distance. There would be a touch more spherical aberration. Alternatively, you can substitute nylon screws for the metal ones. Probably M3 or M4 screws would work.

Note where the focal plane of the camera (sometimes marked with a line through a circle on the side of the camera body) is relative to the top of the focuser when it is in focus. This is approximately the distance the shoulder of the eyepiece (where the insertion barrel meets the upper barrel) needs to be to reach focus.

If the diagonal uses a compression ring, it won't mark your eyepieces. Baader is the only brand with interchangeable barrels on their diagonals to my knowledge. Personally, I really like the GSO/Revelation dielectric diagonals. They do have compression rings on both the 2" holder and the 1.25" low profile adapter.

I've never seen kidney beaning either with this line of eyepieces. Since the blackout touches the edge in your image, it's not kidney beaning you're seeing. Even in extreme kidney beaning, there will always be at least a thin line of visible image near the field stop as you can see in my composite image below: There is a very slight hint of kidney beaning in the 12mm through 25mm versions as seen above, but it was undetectable visually. As such, I would imagine the 8mm below would perform similarly. What you're seeing is probably caused by being too close. Back off from the eyepiece and approach it slowly until the field stop just pops into view. That's the distance you should be observing from. Twist up the eye guard to position your eye at that distance.

The original T1 11mm or the T6 11mm? The former was very rare because it was quickly discontinued due to poor sales.

If your budget is tight, the BST Starguider 5mm is quite good for the money. Here's a composite image of my ~5mm eyepieces I took through my field flattened 72ED refractor:

Well, the Tak TOEs and Vixen HRs are both very good for highest power viewing, although the HRs are getting difficult to find. The TeleVue DeLites are a small step down in ultimate contrast but have much better eye relief and a larger field of view.

Just one or two or a few thousand. 😄