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  #1  
Old 22-01-2019, 01:41 PM
Placesinthedark (Stephen)
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Step up eyepieces

Hi all,



Recently I got a 10" dob and I've been loving the views and enjoying the experience. As with all hobbies you learn more and more the more you put in.



What I've found is I'd like to know what other eyepieces are like. I have a

  • 25mm Kellner (cheapo thing but actually my favourite)
  • 10mm super plossol came with scope and feels restricted to look through
  • 30mm starguider 2" (not bad but the edges of the image are weird and warped)
  • 15mm plossol (again the view is hard to get and feels restricted)


I'd like a planet eyepiece like 5-9mm that doesn't feel like I'm looking through a pinhole, if that's possible??


And a 20-25mm with a nice bright sharp view, the kellner is easy and bring to look through.


Any eyepieces you think could fit the bill at $200 or so each?



Thanks for your time with this
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Old 22-01-2019, 02:18 PM
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DeWynter (ILYA)
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For the planet one try to get Vixen SLV. They are about $200 AUD delivered. myastroshop.com.au has wide range of them. Sorry, no 2.5mm - I got the last one. They have 50 view, but for planetary viewing it's perfectly fine. Image quality is quite high.

For the 20-25mm range try Explore Scientific 68 series. They (20mm and 24mm) are relatively cheap and and would cost you about $200 AUD delivered from US. Not sure who is selling them here in Australia. ES 68 24mm is arguably the best in the 68 series with great image.

If you are willing to pay more then try Explore Scientific 82 Series 30mm - an outstanding eyepiece for very moderate price. Solid piece of glass and metal. Weight 1kg(!!!) About $300 USD. I guess only TV Nagler 31mm or Ethos/Delos can beat it, but at a completely different price.
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Old 22-01-2019, 03:06 PM
Wavytone (Nick)
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Although being in Stanhope suggests you’re a bit isolated I’d suggest attending some star parties and trying other people’s first before buying anything.

Otherwise you risk buying and selling several before you settle on some you like.

Sorry Ilya but wide angle eyepieces don’t need to be big, heavy doorstops, nor the size and shape of Coca-Cola bottles.
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Old 22-01-2019, 03:08 PM
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mental4astro (Alexander)
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There's one thing that is critical to understand about telescopes and eyepieces in oder to make the best choice for YOUR scope - optical matching.

This starts by understanding that all telescopes produce a CURVED focal plane, not a flat one. We are made to think that a telescope focuses to point. This is true only for a single star. But there are stars all across the field of view. When all the stars are plotted at focus across the focus of a scope, you will find that they are spread across a bowl shaped plane. The bowl can be either convex (for refractors, SCT's and Maks) or concave (Newts).

The second part is that it is easier to design EPs for a convex focal plane, and cheaper to manufacture. The concave focal plane of Newts is much more difficult and expensive to design and manufacture EPs.

This is why Naglers, Ethos and the high end Explore Scientific EPs are significantly more expensive than other EPs - these are desinged for Newts.

Match the EP to the scope and you will end up with an image with minimal or no aberrations.

It is when you put an EP designed for the opposite shaped focal that things CAN go pear shaped very quickly with a wide array of aberrations visible, such as astigmatism, field curvature, chromatic aberration, etc.
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Old 22-01-2019, 03:18 PM
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mental4astro (Alexander)
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As Newtonians present such technical difficulties, and Newt specific EPs are so expensive, finding inexpensive and optically good EPs can be difficult - but it's not impossible!

There's a trick to this. And it comes from the complex nature of contemporary EP designs meaning that there are some convex specific eyepieces that actually do a fantastic job in Newts as well. From a given line of eyepieces, take for example the Baader Hyperion line, every single focal length shows significant aberrations such as astigmatism and field curvature EXCEPT for the 5mm! The 5mm Hyperion is sensational in Newts as fast as f/4.

There may be just one, or two or three individual EPs from a whole line that perform really well in Newts, so it is important when reading reviews to make a point of finding out what scope an EP is being used in so you can figure out if the EP being reviewed is good for your Newt or not. As most people do not know about optical matching, they may write off an entire line wholly because they used the EP in the wrong scope design. This is VERY COMMON. The amateur astronomer in the know can "read between the lines" of these reviews.

For some of these less expensive gems, you may need to cope with some mild aberrations, but these will be right the very edge of the field of view, where no one does any serious observing. Accept this, and some absolute and less expensive gems can be had!

Last edited by mental4astro; 22-01-2019 at 04:10 PM.
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Old 22-01-2019, 03:27 PM
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Originally Posted by Wavytone View Post
Sorry Ilya but wide angle eyepieces dont need to be big, heavy doorstops, nor the size and shape of Coca-Cola bottles.
That's true if we are talking about f/9 and slower refractors or short focal length eyepieces. But as soon as we need something like 28mm-30mm and longer with wide field for Newtonians - we are talking about big, heavy and expensive things. Unfortunately...
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Old 22-01-2019, 03:30 PM
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mental4astro (Alexander)
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There is one more thing to understand about Newts, and it has to do with coma correctors. Newts come in a variety of f/ratios, just like every other scope design. What this means is not just a photographic ratio, but describes how deep the focal plane shape is. The faster the f/ratio, the deeper the focal plane. How deep the focal plane is will also dictate how well the EP is matched to its specific shape, convex or concave. So even with EPs designed for a convex focal plane, a particular line will perform better in slower refractors than in faster ones.

What this means for Newts is that Newt specific EPs will show more or less coma depending on the f/ratio, and off course it will be more with faster f/ratios.

How significant coma is as a distracting aberration depends entirely on the individual person. I'll give you my own experience and situation. I have Newts from f/4 to f/5. I only ever use a coma corrector in my f/4 Newt and only with my 30mm 82 eyepiece. Same EP in every other Newt of mine, the eyepiece cleans up the coma really well and I find no need for a coma corrector. A coma corrector is not mandatory in Newts.

What a coma corrector won't do is clean up astigmatism or field curvature. These are different aberrations.

Last edited by mental4astro; 22-01-2019 at 03:56 PM.
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Old 22-01-2019, 04:08 PM
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Stephen,

The weird shape that you are seening at the edge of the field of view of our 30mm is astigmatism. It is the prime symptom of an optical mismatch between scope and eyepiece. The hardest gem EP to find for Newts is long focal length ultra wide angle. I have not found a cheap 30mm EP that doesn't show a lot of astigmatism. Unless you shell out the big bucks for an Explore Scientific or TV, you will need to tolerate a lot of astigmatism.

A little shorter focal length that is bloody good in Newts, especially at f/5, is the Celestron 23mm Axiom LX. Available now only 2nd hand, but inexpensive (less than $150). The Luminos 23mm is not the same design and does not perform anywhere as well in Newts.

A decent and inexpensive 15mm is the GSO Superview. It will show a little astigmatism, but it is not grotesque at f/5. It is also a really easy EP to use as you don't need to struggle to look into it. People tend to hold onto their Superview eyepieces as they perform really well for their price. Best in slower refractors & in SCTs and Maks, but respectable in Newts if you are on a tight budget.

In short focal length EPs, the Explore Scientific 82 line isn't outrageously expensive, usually less than $200 even new.

If your budget is tight, the TMB Planetary Type 2 line is a bargain! They all have a BIG eye lens (the lens you look into) and all have the same generous eye relief meaning you won't need to park your cornea onto the eye lens to look into them, not even the 2.5mm. They will all do a good job in Newts, but the very best performers are the 7.5mm 7mm, 5mm, .5mm, 4mm and the 2.5mm. These were specifically designed for refractors, but in Newts they do very well. You will find these on Ebay for less than $50 each. Do an Ebay search for "SWA eyepiece".

Other people will be able to recommend other gems for your Newt. But all the same read as much as you can, and learn to identify the clues that indicate optical matching or not. It may be just the one single focal length from an entire line, but that's the gem!

Alex.

Last edited by mental4astro; 22-01-2019 at 05:02 PM.
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  #9  
Old 22-01-2019, 05:58 PM
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silv (Annette)
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Awe, Alexander, you did it again. I understood a lot from your again-great posts. If I may ask a question in your thread, Stephen?

Can we tell from the build type https://en.wikipedia.org/wiki/Eyepiece#Eyepiece_designs which EP is designed for correcting concave (Newts) and which convex (refr., CS, Mak)?
For example, if a lens design ends with a concave one nearest the eye-end, it'll correct best in a newt? Or vice versa, a lens design ending with a convex will best correct in a newt?

Will a barlow mitigate or amplify the eyepiece design mismatch in a newton?

Last edited by silv; 22-01-2019 at 06:12 PM.
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Old 22-01-2019, 07:49 PM
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mental4astro (Alexander)
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Great questions, Annette!

I'll start with the barlow. Most people think that a barlow is somehow a neutral or non-active optical element. Thing is there is no optical element that is neutral. ALL are active. This includes the human eye which has its own aberrations unique to every individual, and its own set of corrective capacity. Barlows can both exacerbate and mitigate aberrations, depending on the EP/scope combination.

As for which determining which EP design is best suited to which scope, there's two parts to this. One is knowing that most EPs are designed for a convex focal plane. But remember, this is not a hard and fast rule as EP designs are not geometric in their aberrations. Take the Plossl and Orthoscopic designs. Both are old designs (more than 100 years old). Their lens design/arrangement is the same in all focal lengths, including the glass type. What changes to give the different focal lengths is the thickness of the lens elements and the radii of the various surfaces. And this in turn means that there will be differences in performance between the different focal lengths across all the different scope types AND between focal ratios. Hang on there, I'm coming to a point... The above is to say things are not so straight forward...

Now, the plossl design was made for Newts. But when it was created, Newts were f/7 or slower. You will find that plossl performance is challenged as the f/ratio gets faster.

As for which other designs best suits Newts, this brings me to the second part of the reply. EP manufacturers will never say this. The reason being is as most people think a scope is a scope is a scope, they also think and eyepiece is an eyepiece is an eyepiece. So if a manufacturer were to say that their $200 eyepiece is best for refractors, people will think that there must be something wrong with that line and will not buy it. This leaves us amateurs kicking the can, spending our hard earned money, getting ****ty results with these eyepieces, and dismissing outright entire lines solely because of our ignorance. But all is not lost. It is with threads like this that the how and why of EPs and optics that shed light on the true relationship between EPs and scopes, and everyone learns how to recognize the tell-tale aberrations of optical mismatching. Astigmatism being the key one.

Remember, even between high end EPs, performance will vary between individual EPs, and will again vary between different scope designs and focal ratios, this includes with Newt specific eyepieces. A 20" f/4 Newt will have a focal plane of a different radius from an 8" f/4 Newt, and so EPs will perform a little different again. ALSO, an EP line today is defined by all the EPs first having the same Apparent Field of view, and the same or similar amount of eye relief. The ONLY difference being focal length. So the internal design and composition of the different glass elements, and number of elements can differ tremendously. It is nothing like old EP designs, like the plossl, which was a four element design in two groups. Look closely at the spin on EP adverts today and you will read stuff like "EP design with 5 to 7 elements"... This is not a "plossl" design now, is it. Things are never straight forward.

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Oh, and so you know, to recognize astigmatism, the stars along the edge of the field of view appear as little "seagulls", cocentric to the centre of the field of view. The more grotesque or larger the seagull effect, the more the optical mismatch. Coma makes stars appear as little comets radiating out from the centre. If all you see is coma, THIS IS GOOD! Seagulls not so good, but not necessarily fatal either. It also depends on your individual eyes and your preferences as to how much it bothers you. Recognize astigmatism being described in a review, and you will be streets ahead if the author of the review doesn't!

There is one more line you may like to keep an eye out for your Newts, the Vixen LVW line. Though now discontinued, they are now pretty much just second hand items. One brilliant thing about this line is they are one of the very few lines that perform really, really well across all scope designs! Yes there will be some slight variations, but as a whole they are very bloody good.

Oh, many people also think that the Baader Hyperions are a copy or clone of the LVW's. They are not. They are only similar in size and colour coding, but the Hyperions are designed for a convex focal plane. Their internal design is not any form of copy of the LVW.

I hope this answers some of your questions.
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Old 22-01-2019, 08:55 PM
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Ukastronomer (Jeremy)
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I use Vixen LVW (W is Wide) eyepieces, they are not cheap and very occasionally available pre owned

I mainly use 2" but for 1.25, Vixen, they are quality

This is the new range

https://www.vixenoptics.co.uk/Pages/ssw_eyepieces.htm
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Old 23-01-2019, 10:52 PM
Wavytone (Nick)
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Originally Posted by silv View Post
... Can we tell from the build type ... which EP is designed for correcting concave (Newts) and which convex (refr., CS, Mak)?
For example, if a lens design ends with a concave one nearest the eye-end, it'll correct best in a newt? Or vice versa, a lens design ending with a convex will best correct in a newt?
No, you cannot.

FIRST, four general observations:

A. The problem depends on focal ratio - squared. In scopes with fast f-ratios (f/7 and under) matching the eyepiece to the scope is a significant issue, and at f/4 it is a huge problem. OTOH at f/10 (Celestron/Meade SCTs)it is not an issue and almost any eyepiece made in the past 100 years will work fine.

B. In the US the telescope market is dominated by large fast dobsonians and Celestron SCTs. The two main US eyepiece brands - Televue and Explore Scientific - both have tailored their eyepiece designs specifically to suit fast newtonians, not refractors. What that means will be evident below.

C. In Europe and Japan the telescope market is dominated by small refractors, which have field curvature opposite to that of newtonians, and no coma.

So it should be no surprise that the premium Japanese eyepiece manufacturers - Vixen, Pentax, Takahashi, Nikon, and Masuyama - all make eyepieces optimised for refractors, not Newtonians.

D. The cheap Chinese "budget" eyepieces such as GSO, Prostar and numerous clones... aren't optimised for anything and you're taking pot luck there. But one thing is for sure - they'll all work reasonably well in SCT's.


DETAILS: The real problems are:

1. The aberrations of a complete system (ie telescope + eyepiece+ eyeball) are the sum of the aberrations contributed by each element, ie telescope and eyepiece and eyeball.

A good choice of eyepiece can negate the aberrations of the scope (and the result is very good). For example, Newtonian scope (coma and positive field curvature) plus Plossl eyepiece (negative field curvature) = very good.

A poor choice of eyepiece makes matters worse. For example, Newtonian scope (coma and positive field curvature) plus Erfle eyepiece (positive field curvature) = quite poor.

2. Field curvature of the eyepiece is a parameter that manufacturers do not disclose - in order to keep people guessing and shelling out $$$ to find out the hard way.

3. Coma, or the lack of it, from the scope and whether the eyepiece cancels that. From trying eyepieces in the field with various scopes over 40 years it is quite evident all the Televue eyepieces MUST have some negative coma to cancel the coma produced by fast Newtonians, but those from the Japanese makers do not.

Alternatively if you really want to use an f/3 Newtonian visually, you had better add a coma corrector (eg. Televue Parracor, there are others).

3. Astigmatism, in the observers eye. Televue make a gadget to correct for this - the Dioptrix.

FWIW I use Vixen SLV and SSW eyepieces with my scope, which is a 9" f/13 Rumak. It has a fully corrected flat field - no need to pay the Televue Tax - and doesn't do low power... it starts at 100X and runs to 660X.

Last edited by Wavytone; 23-01-2019 at 11:09 PM.
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  #13  
Old 24-01-2019, 08:31 AM
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mental4astro (Alexander)
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What Wavy and I are saying, to just give a dumb "get this and that eyepiece" is to do you a disservice. It can also create a brand prejudice (in favour or against) based on ignorance or on Brand loyalty, not on optics or understanding or $$$ situation.

Understand HOW EPs and scopes work together, and you will be able to make better choices for YOUR scope and situation. This way you will be able to knowingly work through the flash spin of advertising, the ignorance displayed in many reviews (most unfortunate), and not be seduced by the cheap prices of some eyepieces that in reality will not give you what you want.

Even with expensive eyepieces, there's those that are better suited to different scopes. BIG BUCKS does not guarantee an optical match, nor a performance you seek. Don't forget your eyes are also an active element of the optical train...

There are also those inexpensive gems. But there is a lot of stuff to sort through in order to find them. And an understanding of how scopes and EPs work will not only make it easier to identify them, but may actually give you just what you want without killing the piggy bank.

If you can, do look through as many EPs AND scopes as you can so you can make sense of all Wavy and I have rabbited about. Star Parties are great for this. If getting to a Star Party isn't practical, read carefully and read a lot before laying your money down.

My own kit is a collection of EPs I've cherry picked that have performed brilliantly to my eyes. I have a variety of scopes, Newts, SCTs, Maks and refractors, and they all have different optical characteristics, so I have EPs that are excellent for those scopes, many EPs are scope specific, very few are excellent in all scopes, some are expensive and others are inexpensive gems

Alex.
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Old 24-01-2019, 11:36 AM
Placesinthedark (Stephen)
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Originally Posted by DeWynter View Post
For the planet one try to get Vixen SLV. They are about $200 AUD delivered. myastroshop.com.au has wide range of them. Sorry, no 2.5mm - I got the last one. They have 50 view, but for planetary viewing it's perfectly fine. Image quality is quite high.

For the 20-25mm range try Explore Scientific 68 series. They (20mm and 24mm) are relatively cheap and and would cost you about $200 AUD delivered from US. Not sure who is selling them here in Australia. ES 68 24mm is arguably the best in the 68 series with great image.

If you are willing to pay more then try Explore Scientific 82 Series 30mm - an outstanding eyepiece for very moderate price. Solid piece of glass and metal. Weight 1kg(!!!) About $300 USD. I guess only TV Nagler 31mm or Ethos/Delos can beat it, but at a completely different price.
Thanks so much, will look into ES eyepieces
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Old 24-01-2019, 11:38 AM
Placesinthedark (Stephen)
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Originally Posted by Wavytone View Post
Although being in Stanhope suggests you’re a bit isolated I’d suggest attending some star parties and trying other people’s first before buying anything.

Otherwise you risk buying and selling several before you settle on some you like.

Sorry Ilya but wide angle eyepieces don’t need to be big, heavy doorstops, nor the size and shape of Coca-Cola bottles.
Yes, there is a Toowoomba astronomy club but they don't seem active by their webpage



In that case I would love to try out different eyepieces for sure, but the plossols just seem so constricting for me and I'd love to see more Wide angle stuff.
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Old 24-01-2019, 11:39 AM
Placesinthedark (Stephen)
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Originally Posted by mental4astro View Post
There's one thing that is critical to understand about telescopes and eyepieces in oder to make the best choice for YOUR scope - optical matching.

This starts by understanding that all telescopes produce a CURVED focal plane, not a flat one. We are made to think that a telescope focuses to point. This is true only for a single star. But there are stars all across the field of view. When all the stars are plotted at focus across the focus of a scope, you will find that they are spread across a bowl shaped plane. The bowl can be either convex (for refractors, SCT's and Maks) or concave (Newts).

The second part is that it is easier to design EPs for a convex focal plane, and cheaper to manufacture. The concave focal plane of Newts is much more difficult and expensive to design and manufacture EPs.

This is why Naglers, Ethos and the high end Explore Scientific EPs are significantly more expensive than other EPs - these are desinged for Newts.

Match the EP to the scope and you will end up with an image with minimal or no aberrations.

It is when you put an EP designed for the opposite shaped focal that things CAN go pear shaped very quickly with a wide array of aberrations visible, such as astigmatism, field curvature, chromatic aberration, etc.
Thanks so much for this info! I had no idea I needed to match the scope with the eyepiece. Phew, glad I asked otherwise I might have spent some serious money.



So I might have to bank a bit more cash before I go looking for my next eyepiece...
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Old 24-01-2019, 11:41 AM
Placesinthedark (Stephen)
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Originally Posted by mental4astro View Post
As Newtonians present such technical difficulties, and Newt specific EPs are so expensive, finding inexpensive and optically good EPs can be difficult - but it's not impossible!

There's a trick to this. And it comes from the complex nature of contemporary EP designs meaning that there are some convex specific eyepieces that actually do a fantastic job in Newts as well. From a given line of eyepieces, take for example the Baader Hyperion line, every single focal length shows significant aberrations such as astigmatism and field curvature EXCEPT for the 5mm! The 5mm Hyperion is sensational in Newts as fast as f/4.

There may be just one, or two or three individual EPs from a whole line that perform really well in Newts, so it is important when reading reviews to make a point of finding out what scope an EP is being used in so you can figure out if the EP being reviewed is good for your Newt or not. As most people do not know about optical matching, they may write off an entire line wholly because they used the EP in the wrong scope design. This is VERY COMMON. The amateur astronomer in the know can "read between the lines" of these reviews.

For some of these less expensive gems, you may need to cope with some mild aberrations, but these will be right the very edge of the field of view, where no one does any serious observing. Accept this, and some absolute and less expensive gems can be had!
I've seen the Hyperion at Astro Anarchy for a decent price...I might start with that, but worried a 5mm would only be useful with perfect conditions and optimal cool down.
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Old 24-01-2019, 11:49 AM
Placesinthedark (Stephen)
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Alright, after reading all the excellent and in-depth replies I think I need to just try and go to a star party and try out a bunch. I'm thinking there are a few elements to design and personal preferences which need to be considered - yes, price as well, but seems it's not as a easy and length = perfect choice.



At least it gives me time to save some money and the eyepieces I have aren't hurting me or anything.


Now...to get a drummers chair or some such so I can sit comfortable which star gazing.
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Old 24-01-2019, 02:41 PM
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Yes definitely go to a star party and have a look through different eyepiece telescope combinations and preferably in your own 'scope. Try different focal lengths too.

Other than that give Bintel a call as they currently have Celestron X-Cel LX on sale and these would definitely be a step up from your stock Plossls although I have not personally used these so I recommend advice from Bintel.

See https://www.bintel.com.au/product/ce...v=6cc98ba2045f

and https://www.cloudynights.com/topic/4...-lx-eyepieces/

If budget was not an issue I would recommend Tele Vue as these are highly corrected eyepieces and work well in ANY telescope to f4. Primary mirror coma can also be corrected with the Paracorr. Note primary mirror coma alone is quite insignificant compared to the aberrations caused by a poorly designed eyepiece and a Paracorr won't make a poorly designed eyepiece perform much better other than adding a 1.15x amplification giving a flatter field.

See http://www.televue.com/engine/TV3b_page.asp?ID=2

Tele Vue also make Plossl types and although these are high quality the design still means a small eye lens and short eye relief especcially in the 8 & 11mm.

If you can find a used Nagler, any TYPE (generation) within budget, go for it. Any of the newer types (DeLite, Delos, Ethos) will serve you well too with the first two having the long eye relief. A used Tele Vue Radian would also be excellent value.

Whatever you choose, enjoy!
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Old 24-01-2019, 04:25 PM
Wavytone (Nick)
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Stephen,

Many beginners are struck with the "stick your head in a fishbowl" effect of the UWA eyepieces (Ethos etc) - I agree it is amusing at first and useful on large extended nebulae and a handful of the larger galaxies, but ultimately I regard it as a party-trick.

In some situations UWA eyepieces aren't ideal for getting the most out of your scope on small objects because flooding you eye with things to look at affects your eye's dark adaptation ( ie night vision).

Conversely the smaller field eyepieces (such as Plossls, Orthoscopic, Vixen LV, Edmund RKE) have a much smaller field stop, which simply blacks out a large chunk of the field in your eye. The dark adaptation of your eye responds accordingly and is improved when looking at faint smallish objects like planetary nebulae and small galaxies, as well as the planets at high power. The effect is easily demonstrated in light-polluted urban skies, and even in Bortle 2-3 skies (Blue Mountains) it is noticeable.

A similar technique some use is to cover the observing eye with a black eyepatch while not actively observing, and only uncover it at the eyepiece. This assumes you have two good eyes (I don't) so you won't stumble around tripping over stuff in the dark.

The second aspect to consider is maximising contrast vs scattered light and ghosts in an eyepiece; these are a function of the number of air-glass interfaces in the eyepiece (fewer is better). For this reason some have monocentric or even spherical ball eyepieces (2 air-glass surfaces) which offer the ultimate contrast at the expense of a small field of view.

Many years ago an experiment was conducted in which a group of experienced observers, scopes and eyepieces were tested to find out what magnification/eyepieces were optimal for faint objects - specifically galaxies, as the application was visual searches for supernovae. It concluded that for faint objects there was indeed an optimal magnification - that which gives an exit pupil of 1mm, or X1 per mm aperture of your scope. This is surprisingly high magnification - not low power at all.

Last edited by Wavytone; 24-01-2019 at 04:41 PM.
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