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Old 05-04-2019, 08:49 PM
knightrider
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Looking for 25mm recommendations for a Fast Newt

Hi Guys,

I'm looking for recommendations for a budget 25mm wide/er 1.25" field ep .

Currently just using the packaged Super Plossl that came with the SW 10" Dob. It's the better one, not the cereal box "super 25". It's seems to be fine, pretty crisp, but I haven't tried anything else at this FL so I don't know any better.

Also have the 2" 30mm GSO SV as another low power EP.

My criteria is:

- Budget of $50-$130...?

- Well corrected for a f/4.7 newt @ 1200mm F/L - Looking for a flat field, crisp/sharp/contrasty to 95% out hopefully.

- Wider field than 52 degrees. 60 degrees seems to fit the budget. Unless a good 68 is available..?

- Also....take into account that I'm not using a coma corrector, not really in my budget.


I've done a lot of dredging on the CN and SGL forums on the following:

- 25mm BST Dual ED/AT Paradigm/Agena Dual ED - This FL seems to the weaker ones and doesn't do too well in the outer regions in a fast scope. (I have a 12mm Dual ED and it is eeeexcellent, hoping to get the 5mm version later...)

- 25mm BST UWA 58 degree - Similar story apparently, not that great on the outer regions in a fast scope.

- 25mm Meade HD-60's & Celestron X-Cel LX - Apparently these seem to work well in a fast newt. But would like to hear any experiences of them from any of you guys in this FL.

- 26mm ES62 - Probably out of my price range... I haven't done any digging on these yet.

- 25mm Saxon Cielo HD ED (60 degree) - I can't find anything on these EP's... I would love to know how they perform in a fast scope.

Any other ranges I might have missed worth looking at?


On a side note, not having the experience with a variety of EP's... How do I distinguish the difference between Coma and astigmatism or other distortions at the EP?

Thanks for your input guys

Last edited by knightrider; 06-04-2019 at 04:56 PM. Reason: Grammar + Spelling
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Old 05-04-2019, 09:22 PM
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http://www.moonfishgroup.com/catalog...products_id=50

HIGHLY recommended by BBC Sky at night magazine as a 2" and I have one
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Old 06-04-2019, 12:36 PM
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mental4astro (Alexander)
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Hi Knigtrider,

First, aberrations. Coma is an aberration ONLY seen in reflectors. Many people say they see coma in refractors, they are mistaken. They would be seeing other aberrations, namely spherical aberration and field curvature.

Coma appears as little comet tails that comes off stars, appearing to radiate from the centre. Coma is most apparent at low power and towards the edge of the field of view. Coma IS NOT a flaw in either scope or eyepiece. It is a phenomenon of reflectors and EPs. The faster the f/ratio of the Newt, in this case, the more evident coma will appear. EP design helps a lot in dealing with coma, but these Newt specific EPs are more expensive as it is more difficult to design and manufacture EPs for Newts than other scope designs. Also, the higher you go in magnfication, the less and less coma is apparent. But in your 10" dob, coma is not a significant issue.

Astigmatism is a symptom of an optical mismatch between scope and EP. It appears as little "seagulls" coming of stars, co-centric to the centre, and most evident towards the edge of the field of view. EPs designed specifically for Newts will display NO astigmatism. They may show a little coma, but astigmatism is eliminated. You have seen these seagulls in your 30mm Superview. Maybe you had noticed a "distortion", but that is astigmatism.

Eyepieces do not perform the same regardless of the scope they are used in. EPs are designed first to work with a specific focal plane shape, convex (refractors, SCT's and Maks) or concave (Newts). EPs for a convex focal plane are much easier to design for and cheaper to manufacture. This is why TV's and some Explore Scientific EPs are so pricey. Understand this concept of optical matching an EP to a scope design, and much of the issues written about in reviews begins to make sense and that there is a lot of ignorance about EPs towards scopes. I used to also think "this is an eyepiece, this is a scope, it will work". It is not as simple as this. You've already had an insight that things are not quite like this because of what you are seeing with your 30mm SuperView.

Eyepieces.

When looking for EPs for a Newt, if $$$ are a concern that makes Newt specific EPs too expensive, look for EPs that then best control astigmatism. And yes, it is possible to find EPs that are not Newt specific that actually show no astigmatism in Newts.

DON'T make the mistake of dismissing an entire line/model of eyepiece based solely on a review of one single focal length EP out of an entire line/model. The complex nature of EP design means that while most EPs are not designed for Newts, there can be individual focal lengths from a given line that will actually do a bloody good job in Newts, showing anything from little astigmatism to none at all. If you are prepared to accept just the smallest amount of astigmatism, then a whole lot of really good and inexpensive EPs will come into play as excellent Newt eyepieces.

There's another thing about 1.25" eyepieces, well really all eyepieces regardless of the barrel size. They will only show a maximum amount of sky, and all due to the size of the barrel. Think of it this way, you have two straws, both the same length, but the difference is their diameter, one is wider than the other. You look through each, and which will show a larger amount of the background? The wider one. So you won't find a 30mm 100° 1.25" eyepiece, because the barrel just won't allow it. For that matter you also won't find a 30mm 100° 2" eyepiece either. The longest focal length EP that will give a 100° AFOV in the 2" format is 21mm, and much shorter again for a 1.25" EP.

From your post, I guess you are reacting to the astigmatism that you see through your scope with the 30mm Superview.

Some EP suggestions.

The EP Jeremey kindly posted about will show as much astigmatism in your dob as the 30mm SuperView. It won't show an improvement. You may not be too happy with it if you find the 30mm difficult.

One 23mm 82° that is really blooming good in Newts is the 23mm Celestron Axiom LX. Shows just the smallest amount of astigmatism at the very, very edge of the field of view at f/4.5, and you really need to go hunting for it, & at f/5 even less. It is no longer available new, only second hand. I absolutely loved mine. DO NOT confuse it with the 23mm Celestro Luminos - totally different internal designs and they come from different manufacturers too. You can post an ad in the Wanted forum for this 23mm Celestron Axiom LX.

Of the ones that you mention in your post, I do not have experience with any of these. HOWEVER, knowing now how to recognize astigmatism, when you read through reviews, use this knowledge to help you figure out if the reviewer is seeing any astigmatism IN THAT SPECIFIC focal length, and how much they see. Also look at what scope types the EP the review is used in - if you are looking for an EP for a Newt, tghe review NEEDS to mention the eyepiece being used in a Newt. Do not base your EP decision making on reviews where the EP has not been used in Newts. I did that mistake early on and it cost me a lot of money to learn this lesson. I know better today and I want you to learn it now before you repeat my mistake.

Most people do not understand optical matching between EP and scope, nor the complex nature of contemporary EP design and will dismiss an entire line based on just one single focal length from a given line/model. You can now use the above knowledge to start searching for those Gems of EPs that are both inexpensive and good performers in Newts. It is something I've been doing for a very long time, and slowly been building a bank of such info.

Remember, READ about individual focal lengths in reviews. Do not base your purchasing decisions on reviews about OTHER focal lengths. This will give you the info you need.

Alex.

Last edited by mental4astro; 06-04-2019 at 02:29 PM. Reason: Typo
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Old 06-04-2019, 02:06 PM
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nebulosity. (Jo)
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What a fabulous write up Alex, thank you.
So glad to have stumbled across this post.
Cheers
Jo
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  #5  
Old 06-04-2019, 04:40 PM
knightrider
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Agreed, excellent information Alex. Thanks for the detailed explanation. In my GSO 30mm I haven't been disappointed by it's views by any means, I'm actually quite happy with it. I haven't been spoilt by anything else at this stage so I don't know any better. I have seen distortions at the outer edges but it's far enough out that it's not where I'm looking anyway.

The worst I've seen was in my now gone GSO 15mm SV, distortions/blur started at least 70% percent out in the 10" F/4.7 dob but performed really well in the 6" F/8 dob.

The 25mm super plossl I have I noticed some flare off the stars, I don't recall them being comet tails, more like seagulls. However now that you've explained it, should I expect a plossl to be a good match for my scope? My problem with this one primarily is it's narrow FOV.


I agree with every FL being unique in it's performance in X or Y scope. I expect by the time I finish, every FL EP will be a different brand.
When it comes to reading other's reviews on forums, the hardest thing I find is to determine is what scope their using it in. As I go through them there's many that will recommend an EP even though it's a different FL to what they've used, on top of that many don't state what scope or focal ratio their scope is....and when they do, it normally ends up being a long FL refractor or mak... :/

Last edited by knightrider; 06-04-2019 at 04:41 PM. Reason: grammar
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Old 08-04-2019, 06:18 PM
Wavytone (Nick)
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Cut to the chase.

All plossls should be quite good in a fast newt, if you don't mind the field of view. Likewise all ep's with green letters (TeleVue), Klee Pretoria (which have negative coma and field curvature to match) or Edmund RKE's. ES ones should be OK esp if you like the "head in a fishbowl" effect.

Vixen LVW are good.

Forget Vixen SLV or SSW series, Masuyama or Tak ones - they're for refractors. Likewise Erfles and the clones such as SWA (super-wide-angle) under various names(Prostar, Agena, TMB, APM and others)

Anything else.. try before buying.

Last edited by Wavytone; 08-04-2019 at 06:28 PM.
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Old 08-04-2019, 09:51 PM
knightrider
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Quote:
Originally Posted by Wavytone View Post
Cut to the chase.

All plossls should be quite good in a fast newt, if you don't mind the field of view. Likewise all ep's with green letters (TeleVue), Klee Pretoria (which have negative coma and field curvature to match) or Edmund RKE's. ES ones should be OK esp if you like the "head in a fishbowl" effect.

Vixen LVW are good.

Forget Vixen SLV or SSW series, Masuyama or Tak ones - they're for refractors. Likewise Erfles and the clones such as SWA (super-wide-angle) under various names(Prostar, Agena, TMB, APM and others)

Anything else.. try before buying.
Thanks Nick. The TV stuff is normally out of my price league. I checked out the Vixen LVW too, also a little pricey for me

The "head in a fishbowl" effect of the ES, do you mean it's almost like you need to physically move your head/eyeball all around to circumnavigate the FOV?
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Old 12-04-2019, 02:34 AM
bytor666
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22mm Vixen LVW, best corrected in a fast newt without using a coma corrector. Pricey, but absolute best out of all the ones you mentioned.

However, if you want close to the same performance and not break the bank, another really close in performance is the 2 inch, 22mm Olivon.

https://www.eyepiecesetc.com/Olivon_..._p/7102220.htm
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Old 12-04-2019, 03:23 AM
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Ukastronomer (Jeremy)
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Quote:
Originally Posted by mental4astro View Post
Hi Knigtrider,

23mm Celestron Axiom LX.

Alex.

I must say one of my MOST used eyepieces is an Axiom 19mm, it is lovely

I also have a 9mm LVW again a very nice eyepiece

Just remember they never age, so what may be expensive today is an investment that will stay with you forever.
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Old 13-04-2019, 10:24 PM
ausastronomer (John Bambury)
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Hi Knigtrider,

First, aberrations. Coma is an aberration ONLY seen in reflectors.

Alex.
This is clearly incorrect. Several telescope designs have inherent coma, including Schmidt Cassegrains, Maksutov Cassegrains, Classical Cassegrains, Dall Kirkham and of course Newtonians.

In fact the inherent coma in the Schmidt Cassegrain design led to Meade releasing a modified design Schmidt Cassegrain which they incorrectly called a Ritchey Chretien and after a legal battle they changed the name of the new design to ADVANCED COMA FREE telescope

Quote:
EP design helps a lot in dealing with coma, but these Newt specific EPs are more expensive as it is more difficult to design and manufacture EPs for Newts than other scope designs.
Again this is clearly incorrect and it is something you continually harp on and try to push across with zero substantiation.

The only Newtonian specific eyepiece that has ever been designed and built is the "Pretoria" eyepiece, which had an inbuilt coma corrector. This was sold by University Optics and Brandon (Vernonscope) in the 1980's. When Televue released the paracorr in about 1990 the Pretoria eyepiece died out because the paracorr could be used across multiple eyepieces and was more versatile, particularly when they subsequently released the tunable top version of the paracorr.

The facts are that the eyepieces which perform best in fast Newtonians are eyepiece like Naglers, Radians, Ethos and Delos made by Televue, Nikon NAV HW made by Nikon and a few others, none of which are made by companies that make Newtonian telescopes. It just so happens that the only telescopes Nikon and Televue produce are refractors. Do you seriously think that companies like Nikon and Televue are going to design an eyepiece to work well in Newtonian reflectors, but not work well in the telescopes they design and sell? Fact is these eyepieces work equally well in both Newtonians and refractors and just about any other telescope design you care to drop them in.

Unfortunately Alex, to people new to astronomy, you sound like you know what you're talking about when it comes to optics. To people who have been around a while, it's pretty obvious that this isn't the case.

Cheers
John B

Last edited by ausastronomer; 14-04-2019 at 10:16 AM.
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Old 14-04-2019, 05:55 AM
Shark6
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Fact is these eyepieces work equally well in both Newtonians and refractors and just about any other telescope design you care to drop them in.
That has been my experience as well, having used the same eyepieces in Newtonians, Compound scopes like SCTs, Maks, and Refractors. Scopes ranging from F3.3 to F15.

Last edited by Shark6; 14-04-2019 at 08:30 AM.
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Old 14-04-2019, 10:39 AM
ausastronomer (John Bambury)
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Again this is clearly incorrect and it is something you continually harp on and try to push across with zero substantiation.

The only Newtonian specific eyepiece that has ever been designed and built is the "Pretoria" eyepiece, which had an inbuilt coma corrector. This was sold by University Optics and Brandon (Vernonscope) in the 1980's. When Televue released the paracorr in about 1990 the Pretoria eyepiece died out because the paracorr could be used across multiple eyepieces and was more versatile, particularly when they subsequently released the tunable top version of the paracorr.

The facts are that the eyepieces which perform best in fast Newtonians are eyepiece like Naglers, Radians, Ethos and Delos made by Televue, Nikon NAV HW made by Nikon and a few others, none of which are made by companies that make Newtonian telescopes. It just so happens that the only telescopes Nikon and Televue produce are refractors. Do you seriously think that companies like Nikon and Televue are going to design an eyepiece to work well in Newtonian reflectors, but not work well in the telescopes they design and sell? Fact is these eyepieces work equally well in both Newtonians and refractors and just about any other telescope design you care to drop them in.

Unfortunately Alex, to people new to astronomy, you sound like you know what you're talking about when it comes to optics. To people who have been around a while, it's pretty obvious that this isn't the case.

Cheers
John B
Further reading

https://www.telescope-optics.net/eye...rrations_1.htm

As quoted on Telescope Optics.net and also in Telescope Optics by Rutten and Van Venrooij

"Most objectives generate curvature concave toward objective, and most eyepieces nowadays have near flat field, in which case the combined visual field has curvature similar to that of the objective"

These are the reasons these complex eyepieces work equally well in just about all types of telescopes.

Cheers
John B
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Old 15-04-2019, 10:55 AM
N1 (Mirko)
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I can see how a given producer might want to cater to a certain user group with some of their eyepiece lines by exploiting FC inherent to eyepiece design in order to produce very high performance in a limited number of telescope designs - as opposed to a product that works OK (but no more) across most scope types. All without calling it specific to this or that, obviously.

However, in practice I have yet to come across a severe mismatch between a quality EP and a quality scope in terms of field curvature! I have seen quite a few combinations now, and none performed so badly as to be worth mentioning. All anecdotal of course, and as my eyes age, I might notice FC more in the future.
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Old 16-04-2019, 09:09 PM
knightrider
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Thanks everyone for your suggestions. After a lot of reading I'm settling on the Meade HD-60.

Unfortunately budget is the ruler of the day and won't be able to afford the better more expensive suggestions. But they are still appreciated. And it appears the best way to get the performance in a faster scope is to sacrifice AFOV...which is fine for this FL as I have a 68 deg 30mm anyway.

I will post up with my thoughts on it in the coming weeks after I receive it.
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Old 17-04-2019, 01:04 PM
Wavytone (Nick)
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Mirko then I guess you haven’t tried a premium Erfle in a newtonian !

A few decades ago Erfles were the must-have ultra widefield eyepieces (typically 70 degrees) but they really were only suited to small refractors - they were absolutely horrid things in Newtonians and earned the moniker “Awfle” for good reason. And a curved field was the main culprit - very curved.

Erfle derivatives often branded as “SWA” are still manufactured and are just as awful in newtonians.

Last edited by Wavytone; 17-04-2019 at 01:39 PM.
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Old 17-04-2019, 06:34 PM
ausastronomer (John Bambury)
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Mirko then I guess you haven’t tried a premium Erfle in a newtonian !
Well Nick I guess you haven't tried a premium Erfle in an F5 refractor, because you end up with the same thing, an "AWFLE"

The problem with Erfles is their inability to handle the steep light cone of today's faster F-ratio telescopes. The original Erfle was designed in 1921 and for many decades thereafter, the typical astronomical telescope had an F-ratio somewhere between F6 and F15. They just weren't designed to handle the steep light come of telescopes in the F3 to F7 range, which are commonplace today. Erfle's also suffer from astigmatism, which gets worse as the eyepiece focal length gets shorter. This is the reason you will never find an Erfle with a focal length less than about 12mm and usually not less than about 15mm. A good Erfle in an F8 to F10 Newtonian works very well.

Cheers
John B
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Old 17-04-2019, 07:24 PM
Wavytone (Nick)
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Last encounter with one was brief, John. Put it where it belonged - in the bin - I didn't even have the heart sucker someone else into paying for it. A long time ago I had an ancient Unitron 20mm one in a 0.965" barrel which was OK in my old f/7 Newtonian, but modern ones seem to be worse.
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Old 21-04-2019, 12:17 AM
sharpiel (Les)
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Thanks John. After reading your posts I can sleep more soundly zzzzzzzzzzzzzzzzzzzzz

Your posts usually put me to sleep.

Last edited by sharpiel; 21-04-2019 at 06:53 PM.
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Old 22-04-2019, 06:52 AM
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Um, how am I "clearly wrong"???? Reflectors covers every type of reflecting telescope mentioned. Most curious really

Of course there are some lines that largely perform well in most scope designs. These are very few, and one thing they have in common is they are expensive as these have been specifically designed for this purpose. The Vixen LVW line is one such line. But you will still see performance differences when you swap any of these EPs from one scope to another. In some cases the performance differences are close to imperceptible, and in other cases the performance differences are only a little more pronounced, but there are differences across individual eyepieces when HONESTLY compared in different scope types. When a device like a coma corrector or field flattner is used these variations in performance are greatly reduced or even eliminated. And not everyone finds it mandatory to use a coma corrector or field flattner - this being only for visual use of scopes.

There is no universal one-size-fits-all eyepiece line. Some come close, and there are some individual eyepieces that could be considered "universal", and for some people this is fine. Other people may not be able to afford more exotic eyepieces, and they then need to find what works best for them.

To insist on a universality of a given Brand shows prejudice towards that Brand.

Last edited by mental4astro; 23-04-2019 at 08:57 PM.
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Old 22-04-2019, 05:52 PM
Wavytone (Nick)
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John, generalisms like the one you quoted simply aren't valid for all.

Some of Al Naglers patents are over 40 years old, hardly “modern”. The Smythe lens used in many is a much older idea. Let alone the Erfle and it’s SWA variants, or plossls - still in production and still a good match for newtonians. And the text you quoted... is, well, not exactly recent either.

What’s more recent raytraces of several key designs confirm there are significant variations and that Nagler in particular was using field curvature and sone negative coma to partially compensate these in fast newtonians, while being entirely acceptable in slower scopes without coma and with opposite field curvature - notably f/10 SCTs fir obvious reasons in the US, and to a lesser extent refractors. At f/13 or f/15 (Maksutovs) almost anything looks fine - not only a ramsden eyepiece, even a single element glass sphere used as an eyepiece.

Last edited by Wavytone; 22-04-2019 at 07:31 PM.
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