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Orion Siris plossl eye pieces

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#1 gunny1998

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Posted 19 December 2017 - 11:03 PM

 I have a  6 , 10, 15, 20, 25 and a 32 mm Orion Siris plossl. I also have a 7,10,15 mm celecstron 82 degrees fov  maybe it’s because I’m old and I don’t see that good like it used to but I can’t tell a difference between the plossl and the 7 element celestron as far as clarity ...And I have The xt8i telescope  any thoughts on the siris plossl design ???


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#2 aeajr

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Posted 19 December 2017 - 11:21 PM

I also have the Orion XT8i. Love the scope.

 

Orion Sirius Plossls are very good eyepieces.  I have owned the 25 and the 10 mm and liked them very much.  52 degree AFOV.

 

I have never owned or used the Celestron 82s, so I can't compare them but I would expect the Plossls to stand up very well to the Celestron and many other brands of 82 degree eyepieces for clarity.  I have Meade and Explore Scientific 82s and feel the Orion Sirius Plossls stand up well to these.  

 

One does not replace the Sirius Plossl due to a lack of clarity.  The main limitation on Plossls in general is short eye relief at the shorter focal lengths.   I personally don't use Plossls below 10 mm if I can help it. 

 

In general, people move to 82s for wider field of view and longer eye relief at the shorter focal lengths offered by many makers, not clarity.   


Edited by aeajr, 19 December 2017 - 11:35 PM.

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#3 SeattleScott

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Posted 19 December 2017 - 11:28 PM

I was going to chime in but aejr nailed it. If anything a 7 element lens should be less contrasty than a plossl. If contrast is the only thing you care about a plossl is fine.


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#4 vtornado

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Posted 19 December 2017 - 11:53 PM

Usually what you pay for in an eyepiece is wide fields and edge of field clarity.

 

Most eyepiece designs produce a nice image in the middle of the field of view.  This is also reffered to as

on axis.  My circle T orthos produce the sharpest image of all of my eyepieces, but they have a very

narrow field of view and tight eye relief.   They are uncomforable to use.  I only drag them out when seeing is really top notch and having the sharpest eyepiece gives you better views than a lesser eyepiece with a wider field and more comfortable eye relief.  

 

Why don't you compare your 15mm plossl to your 15mm 82.  You should see a wider field in the 82mm.

Try it on the moon and see how much of the surface you can see in each.

 

Next focus on a bright star in the 82, when it is centered in the eyepiece.  Then push your telescope, so that

the star is now on the very edge.  Is it still in focus?   Is it still round or does it look distorted?  Repeat the

experiment with the 15mm plossl.

 

I find the best tests for eyepieces are the moon, see what the smallest, lowest contrast items you can pick out.

Look for craters that are 2km 4km across.   Look at craters that have ejecta patterns, and see where you kind

of lose sight of the ejecta.

 

Jupiter is another excellent test.   Look for swirling in the bands,  It is rising in the morning.

 

Me personally I don't look at dim objects, I have too much light pollution.  But looking at really dim items

tests transmission, and other properties that bright stuff does not.  Pleades are a good target too. It is wide so

all the stars should be sharp across the field.  If you are in a darker place you may be able to see some

nebulosity.

 

One other thing when running tests and viewing in general make sure your scope is at thermal equilibrium

One way to do this is find a bright star and defocus until you see the concentric rings.  If it looks like "ants" or "worms" are crawling through the image, that means your scope is not yet cool.

 

I have a sirus 25mm plossl.  Excellent eyepiece.  My only better 25mm eyepiece is a celestron silver top plossl made in Japan, and it is only marginally better.

 

Good luck,

VT


Edited by vtornado, 20 December 2017 - 12:01 PM.

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#5 DLuders

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Posted 20 December 2017 - 02:59 AM

For the sizes available in today's marketplace, let's compare the two eyepieces' performance.  I own both of them:

 

$30 Orion Sirius 17mm eyepiece specs (from https://www.telescop...iece/p/8734.uts ):

Apparent Field of View (AFOV) = 52 degrees

Eye Relief = 11mm

Field Stop Diameter = 17.4mm

Number of Lens Elements = 4

 

$100 Celestron Luminos 15mm eyepiece specs (from https://www.celestro...-15-mm-eyepiece ):

AFOV = 82 degrees

Eye Relief = 17mm

Field Stop Diameter = 26mm

Number of Lens Elements = 7

 

The Orion Sirius 17mm is a good eyepiece, but the Celestron Luminos 15mm eyepiece is GREAT.  I let the Orion eyepiece gather dust.  Consider the views you get with your Orion SkyQuest XT8i Dobsonian https://www.telescop...yCategoryId=398 , using the Field of View Calculator https://astronomy.to.../field_of_view/ :

 

Orion 17mm Sirius vs Celestron Luminos 15mm.JPG

 

 

 

 


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#6 Abzmouse

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Posted 20 December 2017 - 03:34 AM

Hi,iv'e never tried the luminous series out but I have tried the orion and the orion is very good, all 10 of the eyepieces I use are mainly plossl except for 5 others that 62° & 60° wideview 6 element design that I find to be faultless. Now without any disrespect intended, iv'e heard and seen this,as people age their eyesight tends to naturally fade,so they tend to not really see any difference which is the fact,other than larger afov in the eyepieces, you can't tell any difference in the contrast of the object your watching and the atmosphere doesn't help with viewing as you age in observation sharpness, but I'm still young, I'll gladly take them 82° afov's of you to try out, I'll pay for the postage, bit with age it's a fact of lifeboat vision dies down slot and you don't see near as well or share say when up to your 50's,this isn't the case for every elderly person but majority it's the fact
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#7 Starkid2u

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Posted 20 December 2017 - 04:27 AM

For the sizes available in today's marketplace, let's compare the two eyepieces' performance.  I own both of them:

 

$30 Orion Sirius 17mm eyepiece specs (from https://www.telescop...iece/p/8734.uts ):

Apparent Field of View (AFOV) = 52 degrees

Eye Relief = 11mm

Field Stop Diameter = 17.4mm

Number of Lens Elements = 4

 

$100 Celestron Luminos 15mm eyepiece specs (from https://www.celestro...-15-mm-eyepiece ):

AFOV = 82 degrees

Eye Relief = 17mm

Field Stop Diameter = 26mm

Number of Lens Elements = 7

 

The Orion Sirius 17mm is a good eyepiece, but the Celestron Luminos 15mm eyepiece is GREAT.  I let the Orion eyepiece gather dust.  Consider the views you get with your Orion SkyQuest XT8i Dobsonian https://www.telescop...yCategoryId=398 , using the Field of View Calculator https://astronomy.to.../field_of_view/ :

 

attachicon.gifOrion 17mm Sirius vs Celestron Luminos 15mm.JPG

Hey, Gunny! A picture's worth a thousand words and this picture says it all! :^)

 

STARKID2U


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#8 Tony Flanders

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Posted 20 December 2017 - 06:50 AM

The Orion Sirius 17mm is a good eyepiece, but the Celestron Luminos 15mm eyepiece is GREAT.  I let the Orion eyepiece gather dust.

Depends on your personal preferences. Personally, I prefer eyepieces with a 50-degree apparent field of view to ones with an 82-degree apparent field of view. I really like to be able to see the entire field stop clearly all the way around without moving my head. As for the eye relief, 11 mm is a tad short but still quite acceptable to me as kong as I'm not wearing my glasses. And an eyepiece's size and weight are a pretty big deal for me. So given that choice, I'd probably pick the Plossl. But I certainly wouldn't complain about either one.

 

My favorite eyepieces have apparent fields of view in the 60- to 70-degree range. Quite a bit bigger than a Plossl, but not so big that I get lost in the field of view. I really don't like that "spacewalk feeling", as Al Nagler likes to put it.


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#9 aeajr

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Posted 20 December 2017 - 09:02 AM

BTW, I have done one on one between Orion Sirius and Meade Super Plossls at near same FL and have seen no difference.   So I would have made the same positive statements about Meade also.   The only Celestron Plossl I have is a 32 and I find it quite good as well.

 

I also have some off brand Plossls and they are quite good too.


Edited by aeajr, 20 December 2017 - 11:07 AM.

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#10 Ken Sturrock

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Posted 20 December 2017 - 11:00 AM

In my opinion: Plossl eyepieces are (usually) wonderful because they are sophisticated enough to have most of the major annoyances corrected, yet the design is readily available and is simple enough that many lower-cost manufacturers can build the eyepieces successfully. As Ed described, it's not a difference of clarity, it's an issue of AFOV and eye relief at shorter focal lengths. In high-magnification situations, especially on a non-tracking mount, the more modern wide-field designs may be more pleasant to use because the eye relief is longer and, because the field is larger, you don't have to be as diligent about nudging the telescope along.

 

I also agree with Tony. I find eyepieces in the 70 degree AFOV range to be my sweet spot.


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#11 Penarin

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Posted 20 December 2017 - 11:44 AM

Plossls are nice eyepieces that have been around a long time.  It's a tried and true design- very sharp and clear.  The only downside is the somewhat narrow 50 degree field of view and the tighter eye relief once you get in the high power range.  Personally I don't mind the 50 degree FOV so I will always have some plossls in my eyepiece case.

 

Plus- and someone can correct me if I am wrong here- plossls tend to stay sharp in scopes with faster focal ratios, like f/4 - f/6.

 

Going to a FOV at or over 80 degrees introduces some complications to an eyepiece.  The complexity of the design, number of elements, size, weight, and cost usually go up in order to provide that larger FOV.  And some widefield designs don't work well in faster scopes.  For example, a 2" Orion Q70 38mm might not be sharp to the edges in a scope at f/5, but it gives you a 70 degree FOV for $90.  A 2" 35mm Tele Vue Panoptic with a 68 degree FOV would probably be sharp to the edge at f/5, but it costs $390!

 

So if you like the view through your plossls, keep using them!  If you prefer the bigger 82 degree FOV on your Celestron eyepieces, go with those.  It's actually fun to compare the views through eyepieces with such different designs.  


Edited by Penarin, 20 December 2017 - 11:45 AM.

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#12 aeajr

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Posted 20 December 2017 - 12:24 PM

 I have a  6 , 10, 15, 20, 25 and a 32 mm Orion Siris plossl. I also have a 7,10,15 mm celecstron 82 degrees fov  maybe it’s because I’m old and I don’t see that good like it used to but I can’t tell a difference between the plossl and the 7 element celestron as far as clarity ...And I have The xt8i telescope  any thoughts on the siris plossl design ???

Gunny,

 

Thanks for asking the question. This has tuned into a very good discussion about eyepieces and why we choose what we choose.  I have marked it for future reference.

 

 

Here are two general reference articles that you and others might find interesting as it relates to eyepieces.

 

 

A very good discussion, by Al Nagler, about eyepieces and magnification for those who want to go a little deeper. He discusses our eyes, our telescopes, focal ratios, exit pupils, the atmosphere and things related to choosing magnification.   A good read and not too technical.  It is a general discussion and not specific to any eyepiece or any brand of eyepiece.
http://www.televue.c...page.asp?id=102

 

 

 

Eyepiece Designs -  This is the one I turn to when I am trying to understand or explain the differences between the various designs.  There are so many different designs.  Many are named for their original designer, such as Huygens, Ramsden, Kellner, Plossl, Konig, Erfle, Branden and Nagler.
http://www.chuckhawk...ece_designs.htm

 

 

I quote from the article as it relates to Plossls.  The Diagrams can be found in the article.

 

Plossl

 

Designed by Georg Simon Plossl in 1860, the Plossl design has become the mainstay of the modern ocular business and probably represents the best value in terms of performance and price, especially in medium and long focal lengths. Celestron (Omni), Meade (Series 4000), Orion (Highlight), Tele Vue, Vixen (NPL) and others offer high quality Plossl oculars. Good Plossls are expensive to manufacture, because they require good optical glass and precisely matched concave and convex doublet surfaces to prevent internal reflections. All Plossl oculars are not created equal.

 

Plossl eyepiece diagram

Plossl eyepiece diagram. Illustation courtesy of Wickipedia Commons.

 

The Plossl optical formula uses four elements in two symmetrical, cemented pairs. Unfortunately, as alluded to in the paragraph above, this symmetry makes Plossl oculars susceptible to internal reflections when viewing bright objects at high magnification, so an internally blackened lens barrel with thread baffles is important, as are blackened lens edges and sophisticated anti-reflection multi-coatings. Inexpensive Plossls lacking these features deliver noticeably inferior views and are not a good value.

 

If well made, Plossls are bright, contrasty, with a flat field, and excellent sharpness. Plossls are usually well corrected and offer about a 50-degree apparent field of view. This apparent field is wider than an Ortho or a Kellner, but not as wide as an Erfle or Radian. Their eye relief is limited to about 70-80% of their focal length. Plossls are available from many suppliers in a wide range of focal lengths in 1.25" and 2" sizes.

 

The focal length range for 1.25" Plossls is about 6mm to 45mm. Plossl oculars are usually parfocal within a given manufacturer's line, which means that when one is in focus, they are all (at least approximately) in focus. Plossls provide adequate eye relief for eyeglass wearers in focal lengths of about 25mm and longer. Non-eyeglass wearers can usually tolerate Plossls as short as about 10-12mm before their eyelashes start brushing the ocular lens.

 

Plossls are useful for most purposes, from short focal lengths designed for planetary views and splitting double stars, to long focal lengths designed for spectacular deep sky views. A 50-56mm Plossl in 2" diameter is spectacular for wide field, deep sky viewing. Telescope companies such as Celestron, Meade, Orion, Sky View, Stellarvue, Tele Vue and Vixen generally supply a 1.25" Plossl eyepiece with their better telescope packages. There are full length articles about Celestron Omni, Meade Series 4000 and Tele Vue Plossl eyepieces on the Astronomy and Photography Online home page.


Edited by aeajr, 20 December 2017 - 12:34 PM.

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#13 drneilmb

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Posted 20 December 2017 - 01:26 PM

Plus- and someone can correct me if I am wrong here- plossls tend to stay sharp in scopes with faster focal ratios, like f/4 - f/6.

 

Going to a FOV at or over 80 degrees introduces some complications to an eyepiece.  The complexity of the design, number of elements, size, weight, and cost usually go up in order to provide that larger FOV.  And some widefield designs don't work well in faster scopes.  For example, a 2" Orion Q70 38mm might not be sharp to the edges in a scope at f/5, but it gives you a 70 degree FOV for $90.  A 2" 35mm Tele Vue Panoptic with a 68 degree FOV would probably be sharp to the edge at f/5, but it costs $390!

Plossls aren't necessarily sharper in scopes with faster focal ratios, instead they are just showing the inner part of the FOV that would be seen in a wider FOV eyepiece.  Said another way, if a 70 degree eyepiece in a very fast scope only shows aberration in the outer 10 degrees of the FOV, then it has the same sharp 50 degree field as a Plossl.

 

That said, for my budget and taste, the sweet spot for eyepiece value is around 60-70 degrees right now. Branded generic eyepieces like BST planetary, Agena Starguider, SWA/Q70 as well as more premium choices like Meade HD-60 and Explore Scientific 68 degree line are very pleasant to use and not (in my mind) unduly expensive.

 

-Neil


Edited by drneilmb, 20 December 2017 - 02:09 PM.

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#14 Philler

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Posted 20 December 2017 - 06:12 PM

I usually avoid these equipment discussions/debates. Many of us who are happily satisfied observing with what we have seem to be forever pressured into thinking what we have is not good enough. That said, I am very happy with my TV and Meade plossls, 26mm, 17mm and 13mm. I've tried other brands of Plossls and they are just not as sharp and don't show objects as consistantly well as my TV Plossls. But for my shorter fL ep's like 9mm and 6mm, as I have gotten older I have gone to the wider fields, longer eye relief ep' with more glass. I bought both the 9mm and 6mm Orion Expanse last year ( both 66 deg AFOV and nice eye relief) and they seem to be as sharp and perform overall just as well as my TV plossls, especially the 9mm Expanse. So, I think I'll stick with TV Plossls in the longer fl's, but anything shorter than about 11mm, I want the wider field and longer eye relief.

Edited by Philler, 20 December 2017 - 06:27 PM.

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#15 Philler

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Posted 20 December 2017 - 10:03 PM

For the sizes available in today's marketplace, let's compare the two eyepieces' performance.  I own both of them:
 
$30 Orion Sirius 17mm eyepiece specs (from https://www.telescop...iece/p/8734.uts ):
Apparent Field of View (AFOV) = 52 degrees
Eye Relief = 11mm
Field Stop Diameter = 17.4mm
Number of Lens Elements = 4
 
$100 Celestron Luminos 15mm eyepiece specs (from https://www.celestro...-15-mm-eyepiece ):
AFOV = 82 degrees
Eye Relief = 17mm
Field Stop Diameter = 26mm
Number of Lens Elements = 7
 
The Orion Sirius 17mm is a good eyepiece, but the Celestron Luminos 15mm eyepiece is GREAT.  I let the Orion eyepiece gather dust.  Consider the views you get with your Orion SkyQuest XT8i Dobsonian https://www.telescop...yCategoryId=398 , using the Field of View Calculator https://astronomy.to.../field_of_view/ :
 
attachicon.gifOrion 17mm Sirius vs Celestron Luminos 15mm.JPG


Shouldn't have to pay $100 for a 15mm, 10mm, or 7mm Luminos. I ordered a 7mm Luminos new for $92 includes 3 day shipping.

Edited by Philler, 20 December 2017 - 10:11 PM.


#16 aeajr

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Posted 20 December 2017 - 10:54 PM

I usually avoid these equipment discussions/debates. Many of us who are happily satisfied observing with what we have seem to be forever pressured into thinking what we have is not good enough. That said, I am very happy with my TV and Meade plossls, 26mm, 17mm and 13mm. I've tried other brands of Plossls and they are just not as sharp and don't show objects as consistantly well as my TV Plossls. But for my shorter fL ep's like 9mm and 6mm, as I have gotten older I have gone to the wider fields, longer eye relief ep' with more glass. I bought both the 9mm and 6mm Orion Expanse last year ( both 66 deg AFOV and nice eye relief) and they seem to be as sharp and perform overall just as well as my TV plossls, especially the 9mm Expanse. So, I think I'll stick with TV Plossls in the longer fl's, but anything shorter than about 11mm, I want the wider field and longer eye relief.

Unfortunately I have to agree with you.  But I see it more as someone waiving a prize in front of me.  If only I would buy THIS eyepiece my life would be better.   

 

I think it is all offered with best intent, but it is hard to listen without being enticed.

 

That is part of the reason I have been pleased to see such strong support for the good old Plossl in this discussion and in another I have participated in recently.   

 

Here's a toast to the mighty Plossl and all the good views it brings us.   Hip Hip Hooray!


Edited by aeajr, 21 December 2017 - 06:21 AM.

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#17 Philler

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Posted 20 December 2017 - 11:28 PM

I usually avoid these equipment discussions/debates. Many of us who are happily satisfied observing with what we have seem to be forever pressured into thinking what we have is not good enough. That said, I am very happy with my TV and Meade plossls, 26mm, 17mm and 13mm. I've tried other brands of Plossls and they are just not as sharp and don't show objects as consistantly well as my TV Plossls. But for my shorter fL ep's like 9mm and 6mm, as I have gotten older I have gone to the wider fields, longer eye relief ep' with more glass. I bought both the 9mm and 6mm Orion Expanse last year ( both 66 deg AFOV and nice eye relief) and they seem to be as sharp and perform overall just as well as my TV plossls, especially the 9mm Expanse. So, I think I'll stick with TV Plossls in the longer fl's, but anything shorter than about 11mm, I want the wider field and longer eye relief.

Unfortunately I have to agree with you.  But I see it more as someone waiving a prize in front of me.  If only I would buy THIS eyepiece my life would be better.   
 
I think it is all offered with best intent, but it is hard to listen without being enticed.
 
That is part of the reason I have been pleased to see such strong support for the good old Plossl in this discussion and in another I have participated in recently.   
 
Here's a toast to the might Plossl and all the good views it brings us.   Hip Hip Hooray!


Yea Ed I hear you. I have thought about going to wider field ep's in 17mm and 13mm to "upgrade" to wider fields, maybe like the ES models. But those 17mm and 13mm TV Plossls that I bought in the 1990's
have given me such great views and exceeded my expectations. I don't think I will ever retire them and I sure ain't gonna sell them. I just save the wide fields for the shorter fL's. like I said.

Edited by Philler, 20 December 2017 - 11:31 PM.

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#18 David Castillo

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Posted 21 December 2017 - 11:52 AM

Lots of things to consider in comparing the two types of lenses. I have used a Barlow on Orthiscopics, Plossls as well as Widefield EPs  for better eye relief and believe that the Plossls and Orthos held an advantage in overall sharpness, and that the Widefields can, in some applications create Kidneybeaning and often are a problem finding a comfortable spot to hold my in head while observing.


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#19 Abzmouse

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Posted 21 December 2017 - 01:15 PM

I personally find plossl eyepieces are best all-rounders, also when it comes to wide field views I think anything beyond 62° isn't necessarily needed
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#20 Philler

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Posted 21 December 2017 - 02:22 PM

Nothing wrong with Orthos. I kind of got away from them in the 1990's when I went to Plossls. I liked the nice eye relief in the longer fl's like my 18mm Ortho (the only one I still have, sold the rest years ago), and the image quality was always good edge to edge. The short comings of Orthos: the 45 deg or less AFOV and short eye relief in the shorter fL's.

Edited by Philler, 21 December 2017 - 02:24 PM.

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#21 Hipoptical

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Posted 04 August 2018 - 05:01 PM

Slightly old thread. Not very communicative at the moment, but I thought I'd jump in on this one. Lots of great information here.

 

I just spent a lot of money on various EPs. I'm going to make a separate thread about that. But I have to say that I am very very impressed with my Sky Watcher 20mm Plossl, so much so that I just ordered the 25mm and the 17mm in their range. 

 

I have some pretty expensive EPs, but I am a noob and just learning the ropes. So take what I say with a grain of salt.

 

The Sky Watcher cost me 20 quid (GBP) which equates to about 26 bucks right now. It's my cheapest EP by far. My most expensive EP cost me about 150 GBP. I must admit, I haven't even had a chance to get that out of its box yet, though I got its little sibling out - pretty stunning views. No regrets at all about spending that much on an EP.

 

But yet, that 20mm Plossl is just absolute magic. Great contrast. Pin sharp stars. The eye relief is acceptable. Even the FOV is acceptable to me (probably not knowing better). I have one 82mm EP in my collection to compare it to, but it's at the other side of the focal range. 

 

I am so impressed with this 'cheap' little EP that I am using it as my main EP for when I get my Telescope set up. It's outside right now, ready to go. The other night was a very rare night here in the UK, but by the time they switched our street lamps off, it had clouded over. Unbelievable bad luck. But I did snatch about 5 seconds of the Moon through this Plossl as it just came over the rooftops. Absolutely stunning. Breathtaking in fact. 

 

The EPs that came with my Orion Starseeker IV 6" Reflector are the 23mm and 10mm SVBONY or Vite aspheric EPs. I like them though obviously they are a bit lacking in my fast f5 'scope. They do barlow well with the included Shorty Barlow. No complaints at all. But remember I'm a noob with nothing to compare to. These EPs are my base line.

 

I've got a few EPs in the higher focal range from 15mm up to 3.2mm. They have a slightly wider FOV. So I thought I'd just get the Plossls around the lower focal ranges and then Barlow them.

 

The Sky Watcher Plossls are just about the cheapest 'name brand' you can get in the UK right now. I only bought it on the off chance after spending much more on a few other quality EPs. I'm so glad I did.

 

I was going to get the Orion Sirius Plossl. It's only a few quid more. But the thing is they look exactly the same as the Sky Watchers. And they are even the identical focal ranges for the whole set. I wouldn't like to venture if they are re-branded Orions, but they do look very similar. It may be they are not as great quality as I have nothing to compare to. And I'm sure they aren't as great as the very high end Televues. But this is a great brand all the same and most definitely a great EP, no matter the price. 

 

You might think I would be a little disappointed that my cheapest EP has become my favourite go to EP, but nothing could be further from the truth. I plumped for buying discrete EPs as opposed to a Zoom because I wanted to learn about EPs and the different designs. I figured I could get a Zoom later on after doing the hard work of learning about different FOV and whatnot.

 

I still have my expensive EPs and they are not going anywhere. They are definitely better, even if not 10 times better, but I understand the law of diminishing returns, so it's ok. 

 

I can understand now why people spend so much on a Televue just to squeeze that extra drop of performance out for their scope. If they can afford it, it's worth every penny. 

 

I can see now there is an intangible quality to the love for certain EPs that is maybe not directly proportional to the cost. I can't wait to get my other Plossls in the post. Then get comparing them to each other and my other EPs. 

 

I'll make another thread about my humble little EP collection when I can gather my thoughts a bit more. But I just thought I'd share my total beginner's experience with you.

 

My advice to any total beginner like myself who has not yet upgraded the EPs that came with their 'scope, would be to buy some lower focal range Plossls and a decent Barlow if they did not yet have one - and from there they can see what they like and fill in the gaps accordingly. And the 3 Plossls I bought (25mm, 20mm, 17mm)  along with a Shorty Barlow would actually cost less than one premium EP. What's more, you would probably want to hold on to them after investing in them, as you fill out the ranges you have decided on with more expensive EPs. 



#22 aeajr

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Posted 04 August 2018 - 06:28 PM

As has been mentioned in this thread, many of us recommend avoiding Plossls shorter than 10 mm because the eye relief becomes very short.  You practically have to put your eye on the glass.

 

other than that, Plossls are very good eyepieces. 



#23 rogeriomagellan

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Posted 04 August 2018 - 07:44 PM

Question to everyone: If his Orion Sirius Plössls eyepieces are brand new, could it be possible that they have better coatings than his Luminos and, thus, it also could be an explanation for the clarity difference?



#24 sg6

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Posted 05 August 2018 - 02:54 AM

Plossl eyepieces are fine if they are good and more relevantly work in your equipment.

Good plossls will give good clear and sharp views, like everything there are cheap ones that do not perform so well.

 

A plossl eyepiece is in its simplest form 2 achromat doublet lens, typically symetrically arranged, and that means a few possibilities. Radaii of faces and orientation of these faces. Plano coinvex are likely used on budget plossls as one face has no curvature so easier/cheaper to produce.

 

TV plossl were oddly the standard "budget" upgrade from supplied items at least here some years ago. And there were a lot of people upgrading again and so a fair used market in them. I bought my TV plossl set all used. Then TV made a big price increase - in honesty prices had remained unchanged for a few years. But one "big" jump seemed to stop them being an inexpensive upgrade. Also the BST/Paradigms appeared at the same time.

 

The Orions will almost certainly be the same as the Skywatcher's. There could be small differences, Orion may have specified different coating. or some other small internal changes. The tie in between Orion and Skywatcher is after all quite big. Easier explanation is that the coating have changed from A to B, or some get one type of AR coatings and others get another. If you have 10,000 lens to coat you coat them in the depositation equipment as quick as possible. If the equipment is set differently then they get different coatings. We have to consider simple mass production approaches.

 

Drawback or one at least of plossls is the eye relief. The eye relief of a plossl is around 2/3 or 70% of the focal length - values are approximate, use whichever conversion best suits. So when you get to around 10mm you only get some 6 to 7mm of eye relief (no use for glasses) and at the 32mm and 40mm you get around 22mm to 24mm and that can be too much. On the short side TV stop at 8mm so around 5.5mm of eye relief. Another question on eye relief is where is it measured from?

 

If yours work at f/5 then you are fortunate, Plossls seem to start "failing" at around f/5, some work, some don't.

 

Concerning cost then TV's are higher, although very good. Then I suppose come Vixens and Vixens in the UK are now a match in cost to BST's. So then numerous factors come into play. Not sure exactly where the Orions stand on cost.


Edited by sg6, 05 August 2018 - 02:54 AM.


#25 Capn26

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Posted 05 August 2018 - 10:56 AM

My Orion plossl came with my xt8. I fully expected to pack it away and forget it. It’s by far the nicest of the three brands (Orion,meade,celestron) I have. Not just in terms of optical clarity, it’s all metal and robustly made.

I too succumbed to the desire to upgrade my EPs. I have four meade 5000 uwas, an ES 24mm 68, and q70. I have been pleasantly surprised by the fact that the 68 is as wide a field as I feel I need. The Meade 82s are great, and going no where. But the 68-70 range is a plenty. And honestly, it’s my 5.5 and 8.8 where I appreciate it the most.

I’m sure someone with far more expertise could explain where my EPs fall short. The q70 isn’t up to the others for sure. But it’s been nice realizing that you can do GREAT viewing with even good ole plossls.
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