Wide FOV EP upgrade for StellaLyra 8"

[HonestGazer]

Hi All,

As the title suggests i am looking for a new EP - I have been enjoying my Celestron X-Cel-LX set (5mm, 7mm, 25mm and 2x barlow) however I am now looking for a wider FOV!

I'm not looking to break the bank (appreciate that is the difficulty with the wide FOV) but want to see what people's recommendations are! Explore Scientific are looking like a good option.

 

[cajen2]

I have the same scope and find the Baader Morpheus range to be excellent. Pentax XWs are also very good but significantly more expensive, and for me, less involving than the Morphs. Is 76° wide enough for you?

[HonestGazer]

It's difficult to say! It should definitely be noticeable over the 60 x-cel. I have done alot of reading/research and 80+ seems to get thrown about alot! 

[wulfrun]

Don't overlook the OVL Nirvana range (82-degree). I only own the 16mm but it's very good value and performs well. I think @Mr Spock owns the full set and might comment if the others are as good.

[Mr Spock]

29 minutes ago, wulfrun said:

I think @Mr Spock owns the full set and might comment if the others are as good.

The other are better! The 16mm has a bit of field curvature towards the edges; the other do not and are sharp right to the edge. Highly recommended and excellent value for money.

[Louis D]

4 hours ago, HonestGazer said:

Explore Scientific are looking like a good option.

They were a good budget option 5+ years ago, then their prices climbed into near Tele Vue territory even pre-pandemic, at least here in the US.  There's a bit of a sale on ES-82s here right now; but even then, the Nirvana ES are a much better value.

[Zermelo]

I would go with the Nirvanas, unless you are prepared to spend significantly more than £100 per EP.

If you really like the ES 82 design, but aren't fussed about the name on the side, you can save a bit here:

https://www.opticstar.com/Opticstar-Ultra-Wide-Angle-XL-Eyepieces.html

[bosun21]

Another thumbs up from me for the Nirvana range. They are great value and are also optically good. I myself prefer the Baader Morpheus eyepieces with 76 degrees.

[Ratlet]

Just did the exact same as you.  The 16mm Nirvana is what I got.  Very happy with my purchase.  I found it had great star colour and was really sharp on axis.  Bit ropey towards the edge but nothing major.  That was in an F5 scope.

It didn't feel like much going up from 60 to 82, but coming down you miss the fov.  

[Guest]

Why not make the jump to a two inch eyepiece?  FLO has a line called Stellarlyra and they have a 14mm 80 degree eyepiece that is really nice.  Yes it does cost more but it is worth the money

[HonestGazer]

Thanks all! I have gone for the Nirvana 13mm, my thought process being that it would be a nice intermediate for DSOs etc. And gets my StellaLyra to a 2mm exit pupil (I hope!)

 

Regarding the 2" I am open to the idea, I just didn't want to spend hundreds.....yet....🤭

[Mr Spock]

3 hours ago, Mike Q said:

Why not make the jump to a two inch eyepiece?  FLO has a line called Stellarlyra and they have a 14mm 80 degree eyepiece that is really nice.  Yes it does cost more but it is worth the money

Why, when the 13mm Nirvana is 1.25", half the price, a third the weight and optically excellent?

[Guest]

1 hour ago, Mr Spock said:

Why, when the 13mm Nirvana is 1.25", half the price, a third the weight and optically excellent?

Because at some point he will end up doing it anyway.  Buy once cry once.  Secondly its an excellent eyepiece that, according to the reviews, compares well against one of the TV 20mm.  Lastly..... 30 percent more light.  Why choke down if you dont have to.  

Edited February 21, 2023 by Mike Q

[Mr Spock]

3 hours ago, Mike Q said:

Lastly..... 30 percent more light. 

Please explain.

[Guest]

12 minutes ago, Mr Spock said:

Please explain.

2 inches vs 1.25 inches.  More area for more light light to come through.  It works with rifles scopes and binoculars and it makes sense that the same would hold true with eyepieces.  All things do have to be equal though.  You cant compare a junk 2 inch to a high end 1.25.  

[Mr Spock]

It doesn't work like that 

[CraigT82]

9 hours ago, Mike Q said:

Because at some point he will end up doing it anyway.  Buy once cry once.  Secondly its an excellent eyepiece that, according to the reviews, compares well against one of the TV 20mm.  Lastly..... 30 percent more light.  Why choke down if you dont have to.  

It’s the field stop diameter you want to look at. Generally they are around the same number as the focal length or a few mm more or less. If you have a two inch 14mm EP and it’s field stop is 18mm let’s say, then there’s no point in it being a two incher, it’s just more weight. Any EP with a field stop of less than 31.7mm might as well have a barrel size of 1.25”.

Essentially If you have a 2” EP and a 1.25” EP, both with the same FL, then the two incher will show more sky only if it’s field stop is larger than the 1.25”

[rwilkey]

On 20/02/2023 at 15:44, Louis D said:

They were a good budget option 5+ years ago, then their prices climbed into near Tele Vue territory even pre-pandemic, at least here in the US.  There's a bit of a sale on ES-82s here right now; but even then, the Nirvana ES are a much better value.

Hi Louis, I bought all the ES 82's from Agena Astro before the prices went up and they appeared in Europe and the UK, still stunning eyepieces, but agree with others that the OVL Nirvana looks to be a good budget option.

[Louis D]

13 hours ago, Mike Q said:

More area for more light light to come through.  It works with rifles scopes and binoculars and it makes sense that the same would hold true with eyepieces.

You're mixing up objective lens diameter which does indeed collect more light the larger they get with eyepiece field stop diameter which simply controls the extent of the projected image circle visible in the apparent field of view (AFOV) which then equates to the true field of view (TFOV).

A 2" eyepiece may or may not show more TFOV than a 1.25" eyepiece of the same focal length.  It depends on the diameter of the field stop.  It also depends on the size of the eyepiece's field lens (the bottom-most one) to a lesser extent.  An oversized field lens has no effect on TFOV, but an undersized field lens can lead to edge vignetting.

In general, a 2" eyepiece will indeed have a larger AFOV than a 1.25" eyepiece given the same eyepiece focal length, but not always.  Sometimes, the designer(s) chose to package the eyepiece in a 2" barrel simply due to weight and bulk concerns overwhelming a 1.25" focuser and/or diagonal.  Sometimes the choice was made because there would have been some vignetting if they hadn't.

The classic example of this choice is the 17mm Nagler T4 in a 2" barrel versus the 18mm Meade 5000 UWA in a 1.25" package.  Both are/were 82 degree AFOV eyepieces, but the latter suffers from edge vignetting while the former does not.

[Don Pensack]

It's a little more complicated than that.

All positive eyepieces can have a field stop the same diameter as the inside of the barrel, maybe a tad smaller to allow for a field stop.

But negative positive designs max out with a field stop that is smaller than the inside diameter of the barrel because the field lens expands the image after passage through the lens.

As a result, an all-positive 2" eyepiece can have a field stop of 46-46.5mm, whereas a negative-positive design maxes out at 42-43mm.

In a 1.25" eyepiece, field stops of 27-27.5mm are common in all-positive designs, but 24.5mm seems to be the maximum for a negative-positive design.

It is the reason why an APM UFF 24mm has a 27.5-27.6mm field stop and is 1.25", while a 20mm T5 Nagler had a 27.4mm field stop and was a 2".

 

Louis points out that a designer can go too far in shoehorning a too-large field stop into a smaller barrel.

The Meade series 5000 18mm UWA went from a 1.25" to a 2" diameter to reduce vignetting and it only had a 24.3mm field stop.

[Louis D]

17 hours ago, Don Pensack said:

But negative positive designs max out with a field stop that is smaller than the inside diameter of the barrel because the field lens expands the image after passage through the lens.

You should qualify that with effective field stop for negative-positive designs.

I know for a fact that the physical field stop of the 12mm ES-92 is 51mm in diameter because I measured it with a micrometer in my surplussed version of it that lacks its Smyth group.  Due to vignetting or some other artifact, it measures out as a 48.4mm field stop diameter photographically when used in a scope, however.  It requires about 21mm extra in focus relative to its shoulder to reach focus because the field stop is so far above the shoulder.

If its off-axis chromatic aberrations could be reigned in with an appropriate corrector lens, it would make for a fantastic widest field eyepiece.  I was just out last night quite happily cruising the Orion constellation with it in a 6" f/5 GSO Newt.  If you look straight on axis, the chromatic aberrations are all but undetectable in peripheral vision.  Eye relief is fantastic and the enormous 92 degree AFOV is easy to hold thanks to very little SAEP with the Smyth group gone.  The higher magnification and slightly wider TFOV than my 40mm Meade 5000 SWA or 40mm Pentax XW-R make the view much more engaging than either of those 40mm options.

[Stu1smartcookie]

I hope the OP is following all the above , or , doesn't think he's reading an exert from a topic on Cloudy Nights ! ... all getting a bit heavy , isn't it ?

Pretty simple question of a suitably widefield EP wuithout breaking the bank !  two suggestions , Nirvana or Explore Scientific , both proven . Just personal choice ! Reviews can be gleaned on this forum , somewhere , i imagine . 

 

[Mr Spock]

He's already bought the 13mm Nirvana. Everything else is, well... 

[HonestGazer]

1 hour ago, Stu1smartcookie said:

I hope the OP is following all the above , or , doesn't think he's reading an exert from a topic on Cloudy Nights ! ... all getting a bit heavy , isn't it ?

Pretty simple question of a suitably widefield EP wuithout breaking the bank !  two suggestions , Nirvana or Explore Scientific , both proven . Just personal choice ! Reviews can be gleaned on this forum , somewhere , i imagine . 

 

My mind.....is blown lol 😆  I went for the 13mm Nirvana as @Mr Spock mentioned! Aim is to get near a 2mm exit pupil which from my research I have read is a good intermediate for DSOs etc.

[John]

1 hour ago, HonestGazer said:

My mind.....is blown lol 😆  I went for the 13mm Nirvana as @Mr Spock mentioned! Aim is to get near a 2mm exit pupil which from my research I have read is a good intermediate for DSOs etc.

Good move on good advice - it's no surprise that the first Nagler introduced was a 13mm as was the first Ethos. A very useful focal length in many scope specifications.

I've really liked the Nirvana's that I've used 👍

Edited February 23, 2023 by John