TS Nirvana 16mm 82 degree

[Ags]

I just got one of these, so I thought I would put some thoughts online about it. I am using it primarily in a short refractor (ST80), for scanning the sky for targets for closer examination in Skymax 102 mounted alongside it.

I am comparing the Nirvana to Explore Scientific 6.7/82 and 24/68 eyepieces and Speer WALER 10/82. Also to a Skywatcher Super 25, which is my current finder eyepiece for the ST80.

In terms of design it strongly resembles the Explore Scientific 82 line, being almost exactly the same shape and size as my ES 6.7mm. Even the pattern on the rubber grip is the same, and they are both purged with inert gasses. The 16mm is a bit lighter than the 6.7mm.

First off it is a good spotting scope eyepiece for day use, giving very clear and sharp views at a useful 25x magnification in my ST80. It is really comfortable to use and look through by day.

At night: So far I have only been able to test it on a few bright stars through haze. The seeing was very stable with clear diffraction rings. I would say the Nirvana is less sharp than my ES 24/68, with (first magnitude) stars going a bit fuzzy from 2/3 of the way out from the center in my F5 scope. Even in my F13 Mak I still saw some edge fuzz. I could refocus to bring the edge stars into focus, so perhaps I am seeing field curvature - understandable in an ST80 but not so much in a Mak...? Focusing on the stars halfway from center results in sufficient focus across the field, but it feels like a poor compromise and the ES 24/68 is much sharper with a bigger field. So that is a bit disappointing. Also I expected complete sharpness from the Nirvana in the Mak, and I didn't get that.

The only DSO I saw last night was the double double. In the Mak the Nirvana gives 80x magnification, and it could clearly split the system into its four components, so I thought that was quite good performance on axis.

The real test will come on the next available dark night, when i can test the eyepiece for its intended purpose: picking out faint fuzzies. The ES 24/68 is a superb eyepiece but the 5mm exit pupil it provides shows a literally white sky background from my city location; even very bright DSOs only show as faint hints and stars seem significantly fainter than at higher mags.  So I am hoping for better contrast at the 3mm exit pupil of the Nirvana.

[Ags]

A patch of clear sky blew overhead tonight so I put the Nirvana through its paces on some real DSOs.  Firstly I rebalanced the setup for the Nirvana - it is a bit heavier than a Super 25!

First up were M13 and M92. The darker sky background in the Nirvana (and greater magnification) did make these DSOs stand out from the background better, although they are easily bright enough to be found using a 24mm eyepiece. The Nirvana also gave nice zoomed in views of the globulars when I put it in the Skymax, partially resolving the stars in M92.

I find the Ring Nebula challenging to find using the Super 25: at such low magnification it is simply star-like and the poor contrast means some nights I failed to find it at all despite knowing exactly where it is! It was still a difficult spot with the Nirvana but I think at least a bit easier. Conditions were not great, when I switched to the Mak the Ring was very poorly defined. Perhaps conditions were against the Nirvana finding this target easily tonight.

Tonight I was not bothered by the field curvature I noticed last night. Using the eyepiece normally, it seemed sharp and satisfying. I guess I should just avoid positioning first magnitude stars at the field stop!

[Ags]

Had another session tonight. Tried to hunt down some really faint targets unsuccessfully. I find the eyepiece enjoyable but not top notch optically. Particularly when hunting planetary nebulae, the lack of sharpness in stars means the search is much harder. When you are simply looking at an object, you don't notice the optical defficiencies, but when hunting for DSOs you do pay close attention to the whole view.

Thinking now that I may have to upgrade to a 16mm Nagler at some (distant) point, but this Nirvana will do for now - certainly in an ST80.

[Louis D]

33 minutes ago, Ags said:

Had another session tonight. Tried to hunt down some really faint targets unsuccessfully. I find the eyepiece enjoyable but not top notch optically. Particularly when hunting planetary nebulae, the lack of sharpness in stars means the search is much harder. When you are simply looking at an object, you don't notice the optical defficiencies, but when hunting for DSOs you do pay close attention to the whole view.

Thinking now that I may have to upgrade to a 16mm Nagler at some (distant) point, but this Nirvana will do for now - certainly in an ST80.

You might want to try a 17.5mm Morpheus.  They seem to have been well received.  The 14mm Morpheus I own is nice, but not perfect.  The 17.5mm is supposed to be much better.  However, since I have a 17mm ES-92, 17mm Nagler T4, and 17mm Astro Tech AF70, I can't justify getting the 17.5mm Morpheus just to verify the claims.

[John]

1 hour ago, Ags said:

Had another session tonight. Tried to hunt down some really faint targets unsuccessfully. I find the eyepiece enjoyable but not top notch optically. Particularly when hunting planetary nebulae, the lack of sharpness in stars means the search is much harder. When you are simply looking at an object, you don't notice the optical defficiencies, but when hunting for DSOs you do pay close attention to the whole view.

Thinking now that I may have to upgrade to a 16mm Nagler at some (distant) point, but this Nirvana will do for now - certainly in an ST80.

I upgraded from a 16mm William Optics UWAN to a 16mm T4 Nagler and wondered what the additional £'s that I had to put in actually got me. Maybe this new shape Nirvana is not the same optically as the old shape UWAN / Nirvana though ?

The T4 Nagler 16 is very sharp but it's eye relief is quite tight - 10mm quoted but perhaps more like 7-8mm actually useable ?

 

[Ags]

Indeed I was aware of the reputation of the Nirvana and bought it on that basis. When I upgrade to an ED72, I may also invest in a 2" diagonal and an an ES 18/82 eyepiece. It has 13mm eye relief, so they say (which is the lowest of the whole ES 82 line). Because the ED72 is F6, I could get the same exit pupil from an ES 20/68 eyepiece and stay with 1.25" accessories so that's another thing to consider. Also 68 degrees AFOV is better for a finder eyepiece that 82 degrees AFOV.

[iPeace]

6 hours ago, Ags said:

Also 68 degrees AFOV is better for a finder eyepiece that 82 degrees AFOV. 

A first read, this seems counterintuitive to me; all things being equal, a wider field of view would show more sky and make it easier to find and hop. What am I overlooking here?

[Ricochet]

6 minutes ago, iPeace said:

A first read, this seems counterintuitive to me; all things being equal, a wider field of view would show more sky and make it easier to find and hop. What am I overlooking here?

68° is about the angle that you can concentrate on without moving your eye. In addition the 82° and 68° eyepieces are different focal lengths so the TFoV will be about the same. 

[Ags]

Yes, that's my reasoning.

I have added the Morpheus 17.5 to the list having read a few reviews. I had sworn to never buy a Morphy because they are simply so ugly - with their noisy rubber grip and shouty luminescent lettering, they look like they have been made from offcuts in a Nike shoe factory!

I have also written to TS about the eyepiece... Maybe I've got a dud.

[John]

1 hour ago, Ricochet said:

68° is about the angle that you can concentrate on without moving your eye. In addition the 82° and 68° eyepieces are different focal lengths so the TFoV will be about the same. 

But ...... I find that wider fields are still more use for finding things. You can cast your eye around the field and pick stuff up, often using averted vision, that might otherwise be overlooked.

It's a personal thing though, I appreciate that

 

[Ricochet]

2 hours ago, Ags said:

I have also written to TS about the eyepiece... Maybe I've got a dud.

Good idea. ES recalled a whole batch of eyepieces recently because a lens or element had been installed the wrong way around. Perhaps something similar has happened here. 

 

[Ags]

I used the eyepiece extensively tonight on the Moon. It really is a confusing eyepiece, and seems to need to be focussed very carefully... In the ST80 at F5 it gave a small, sharp and pleasing image of the Moon that degraded significantly in the outer third of the view. Stopping the ST80 down to F8 sharpened up the outer part of the FOV. Switching to the Maksutov, the Moon was lovely! Really big but not too big, and very detailed.

Testing on starfields again, I feel tonight at least that it is good enough, if you focus on a star 50% out the view is sharp across 80% of the field. Beyond that field curvature is the least of the problems, and astigmatism and other aberrations predominate.

[Louis D]

Did you try refocusing for the edge in the ST80?  Short refractors have strong field curvature.  I use a TSFLAT2 ahead of my 2" diagonal to flatten the field in my AT72ED.  I couldn't stand using it without it after having used much longer focal length Newts which have a much flatter fields as a result.

The radius of curvature for your ST80 is about 1/3 of the focal length or (80*5)/3=133mm.  For an 8" f/6 Newtonian, it is the same as the focal length, 1200mm.  That means the ST80's field is massively curved compared to the Newt.  In my AT72ED, it's about the same as your ST80, 432/3=144mm, and no wide field eyepiece shows pinpoint stars to the edge in it without the field flattener.

[Ags]

Yes, I have taken to focusing on a star 50% from center. That keeps 80% of the field sharp enough, but doesn't help the outer 10-15% of the field, where the stars are smeared into arcs parallel to the field stop. Strong astigmatism in my opinion. Also, bright stars in the extreme outer field grow a long blue finger pointing back to the center of the field.

[Louis D]

1 hour ago, Ags said:

Yes, I have taken to focusing on a star 50% from center. That keeps 80% of the field sharp enough, but doesn't help the outer 10-15% of the field, where the stars are smeared into arcs parallel to the field stop. Strong astigmatism in my opinion. Also, bright stars in the extreme outer field grow a long blue finger pointing back to the center of the field.

In that case, focus back and forth on either side of best focus at the edge.  Stars should go from tangential smears to radial smears if astigmatism is present.  At best focus, they look sort of like a bloated cross.  The blue finger is chromatism tossed in for good measure.  It should decrease in length as the star is moved from the edge toward the center while refocusing.

[Ags]

On 16/05/2019 at 19:45, Louis D said:

focus back and forth on either side of best focus at the edge.  Stars should go from tangential smears to radial smears if astigmatism is present.  At best focus, they look sort of like a bloated cross.

I had a chance to try this tonight, and that's exactly what I saw with the Nirvana. I spent an hour going back and forth between all my eyepieces. Astigmatism is apparent in the ES 24/68 and ES 6.7/82 but to a lesser extent. The Speer WALER 10/82 was by far the best, showing hardly any astigmatism at all! 

In conclusion, the 16mm Nirvana is not perfect but it is not that different from other eyepieces I have been happy with. Using the Nirvana as a finder eyepiece draws my eye away from the center and out to the very edge however.

[Louis D]

3 hours ago, Ags said:

I had a chance to try this tonight, and that's exactly what I saw with the Nirvana. I spent an hour going back and forth between all my eyepieces. Astigmatism is apparent in the ES 24/68 and ES 6.7/82 but to a lesser extent. The Speer WALER 10/82 was by far the best, showing hardly any astigmatism at all! 

In conclusion, the 16mm Nirvana is not perfect but it is not that different from other eyepieces I have been happy with. Using the Nirvana as a finder eyepiece draws my eye away from the center and out to the very edge however.

I almost feel bad because once you see astigmatism, you can't unsee it.  This leads to a quest to get rid of it at any expense which tends to flatten the wallet.

[Ags]

Jupiter is difficult from my garden this year. I had a look at it tonight for the first time this year, just skimming the top of the wall at the South end of the garden. I particularly wanted to see how it would look in the Nirvana at 81 magnification (using the SkyMax 102 of course).

Although the magnification is quite moderate, it was pleasing to view the planet without the usual clouds of floaters intruding. I had the feeling that I could study the planet properly without having to continually shake my head to shift the floaters. Sadly the seeing was atrocious with the whole disk of Jupiter fragmenting at times. There were very few moments of stability, but in those brief moments the Nirvana was giving a sharp, contrasty and colorful view.

Being so low, Jupiter was fringed at top and bottom with blue and red so I tried adding a light yellow filter to cut the atmospheric dispersion, and I think it helped, but I can't really say as the seeing got even worse at that point.

[Louis D]

49 minutes ago, Ags said:

Jupiter is difficult from my garden this year. I had a look at it tonight for the first time this year, just skimming the top of the wall at the South end of the garden. I particularly wanted to see how it would look in the Nirvana at 81 magnification (using the SkyMax 102 of course).

Although the magnification is quite moderate, it was pleasing to view the planet without the usual clouds of floaters intruding. I had the feeling that I could study the planet properly without having to continually shake my head to shift the floaters. Sadly the seeing was atrocious with the whole disk of Jupiter fragmenting at times. There were very few moments of stability, but in those brief moments the Nirvana was giving a sharp, contrasty and colorful view.

Being so low, Jupiter was fringed at top and bottom with blue and red so I tried adding a light yellow filter to cut the atmospheric dispersion, and I think it helped, but I can't really say as the seeing got even worse at that point.

I've got trees blocking my view of Jupiter until early in the morning from my backyard, so I haven't gotten a look at it yet.  I'm over 20 degrees latitude south of you, so I should be able to get a decent view of it.

Glad you're enjoying the Nirvana.