Louis D

Well, it's like having a minimum of 6 eyepieces in one, perhaps more if you dabble in half-mm focal lengths. So, that makes just over 2 pages per covered focal length! That doesn't seem so excessive then.😁

How long did you allow for acclimation? I see spiking with my 90mm triplet APO that looks like pinched optics for up to about 30 minutes. It eventually disappears after acclimation. Give your scope an hour to acclimate and check again.

I kind of wondered if/suspected based on the 50 degree AFOV.

Has anyone discussed theories on the optical and mechanical organization of the Televue Nagler Zooms and the Svbony 3-8mm zoom? My theory, they have a 4 element image forming positive group up top and a 2 element negative, Smyth, group down in the insertion tube. To increase magnification, they simply move the two groups apart like a varifocal eyepiece such as my Speers-Waler 5-8mm "zoom". This also maintains the size of the AFOV as in the S-W. The mechanical trick to maintain near parfocality is to move the negative lens group downward during zooming in (higher power). I have to do this with the focuser knob to maintain focus while zooming in with the S-W.

On axis, off axis, edge, all? At 3mm, it is very good across 70% of its field. It's only in the outer portion it starts to fall apart in faster scopes. I have no idea how well corrected the 3.3mm TOE is edge to edge. Most folks only discuss on, or nearly on, axis performance of it and the Vixen HRs since few use these eyepieces for anything but planetary viewing or double star splitting.

That 38% linear secondary obstruction doesn't sound very conducive to good planetary contrast.

If it sharpens up refocused, it's entirely field curvature. If it is still mushy, just less so, then there's most likely astigmatism involved as well. It's best to use a star to examine these effects. Astigmatism turns stars in lines. They'll be tangential on one side of focus and radial on the other side. You'll also be able to see chromatic aberrations which turn stars in to radial rainbows. Coma is rare in well corrected eyepieces in my experience. As a rule of thumb, if an eyepiece exhibits chromatic issues, it will generally also exhibit coma. This manifests itself as a rainbow that fans out center to edge. It gets more diffuse the closer the star is moved to the edge. A coma-free eyepiece shows a nice linear rainbow pointing to the center.

I've found my 90mm Triplet takes about 30 minutes or longer to acclimate, or I get what looks like pinched optics. That might just be due to a poorly engineered objective cell with a coefficient of expansion greatly mismatching that of the glass. What I'm seeing is definitely not tube currents during acclimation. I forget where I read it, but eyepiece acclimation is much less of an issue due to the smaller total thermal mass, and the fact that it is at the back end of the optical train where variance in the optical figure has less effect than at the objective. As for dew heaters, the trick is to use as little as possible. You want to warm the optical device just above the dew point. That generally won't noticeably affect the figure of the optical element.

I buy flat field eyepieces to work toward with non-flat field scopes. Once I added a coma corrector to my Newts, it reduced their low curvature even more. I then added TSFLAT2 flatteners to my 2" diagonals to flatten my refractor fields. I was even able to compensate for the field curvature of my 14mm Pentax XL by over-correcting the field flattening with the TSFLAT2 by increasing the working distance another inch or so, IIRC. It was amazing to see the XL sharp edge to edge without refocusing.

No, you don't need to ever justify a purchase to anyone else (except perhaps your family CFO, if you know what I mean). I'm just trying to figure out what I've been missing with this scope. I'll try some more widefield viewing with it.

My 152 Achro is fine for sweeping star fields, but so is a 6" f/5 Newtonian which is much lighter, cheaper, and color free. The 152 does very poorly on planets and double stars at moderate to high power thanks to excessive CA. DSOs appear about the same as in the Newt. @Stu1smartcookie What exactly do you find the 152 Achro to do particularly well or better than other comparable scopes? The only thing I've found it good for is extreme testing of violet-cut and red-cut filters to find out which (combination) yields the best image of various objects. Because I love tinkering with optical combinations, I find it fun. I'm trying to justify why I'm holding onto it.

I tried them both in the 72ED, 90 APO (both with TSFLAT2 field flatteners), 8" Dob with GSO CC, and 127 Mak. I don't think I had the 6" f/5 Newt or 152 Achro at the time. Both performed pretty consistently across all of them except for the slow Mak which closed the gap between them. I will say the background seems darker in the NT4 than the Redline. It might be for the same reason as with the Vixen LV line appearing darker: the use of rare earth glass types that contributes to their higher prices relative to their competitors.

I won't lie, the 22mm NT4 is nice and sharp edge to edge compared to the 22mm Redline 70. It was enough different to persuade me to retire the Redline to the B-Team case in favor of the NT4 despite the tighter eye relief and slight SAEP in the NT4.

If you look down the tube from the open end, you should see a magnified image of your face like in a shaving mirror when you have your head at the right distance above the end. It's generally around 6 to 10 inches above the end, IIRC. This is just a quick test to see if the mirror can produce any sort of image.

Will probably need a photo down the tube to see if the spider and optics are still there.

APM claims it weighs 331g. I'll have to get it and my gram scale out again to double-check.

Just checked their pricing at CCTS. $119, and they don't charge sales tax to Texas! That's only 20% higher than the 2010 price I paid. I bought my Arcturus binoviewer from them, so I've had a positive experience with them in the past.

I don't recall FC being much of an issue, but the notes in my review/report does state I noted a tiny bit. It must be pretty minor compared to my Pentax XL 14mm which I had to retire after my eyes went fixed focus in my mid-40s. I'll have to look for FC in the Svbony the next time I have it out.

I weighed my APM UFF 24mm to be 346g. Weird that it's heavier than the Altair version.

My 25mm A-T Paradigm (Starguider) has 17mm of usable eye relief with the eyecup all the way down, so identical to the 24mm UFF with eye cup folded down. I've not measured the eye cup up eye relief of either.

Sounds about right. The eyeglasses view in the 22mm Nagler is still wider than the Redline 22mm 70 degree by a few degrees.

I've measured my two 32mm Plossls (a GSO Super and an Orion Sirius) as both having 15mm of usable eye relief. They are right at the limit of usable with eyeglasses for me. I've measured the APM UFF 24mm as having 17mm of usable eye relief which is comfortable to use with eyeglasses resting on the folded down eye cup. I skipped the Meade 5000 SWA 24mm when it went on clearance sale a decade ago because of its tight usable eye relief. The optically identical ES-68 24mm is even tighter due to slight eye lens recession. Ernest in Russia has measured it as having 11mm of usable eye relief.

IIRC, rings on one side of focus and smoother on the other side indicates spherical aberration of the objective. Refer to telescopeѲptics.net Refracting Lens Objective page for more information. I've grabbed a snippet of the spherical aberration explanation below:

It just depends on the use case if you can live with its tight eye relief. Try keeping it around for planetary observing where quickly changing focal lengths depending on second to second seeing conditions is a huge plus. It's fine then because you don't need to take in the entire field of view at once as you might for lunar or starfield observing. With eyeglasses, you lose some outer field. Even without eyeglasses it's difficult to take in the outer field at the shorter focal lengths without tilting your head. Sure, you could Barlow an APM Super Zoom, but that combo is huge in comparison. It would be similar to me choosing to use my Speers-Waler 5-8mm zoom:

Yes, very similar. Distortion characteristics account for the difference in apparent field of view. The ES-68 will tend to stretch things toward the edge more than the UFF. Thus, the moon will remain more round shaped and less egg shaped in the UFF. In my comparison image below, note how little distortion the APM UFF 24mm has center to edge. The rulers maintain roughly the same height edge to edge, and the individual millimeter markings maintain similar spacing center to edge. You may need to select and enlarge the image to see this level of detail. Now notice how much the Tele Vue Panoptic 27mm distorts the rulers' height center to edge. This is how the the TV Panoptic 24mm would appear. Since the ES-68 24mm is a design copy of the Panoptics, I would expect it to have similar center to edge distortion. The Panoptic 24mm would be just as sharp center to edge as the 27mm version if you demand perfection. The ES-68 line tends to lag a bit behind the Panoptics they copied in edge correction. It could be the designer chose to use less expensive glass types that don't preserve edge correction as well.