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Yogesh

Explanation on different eyepiece types

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Hi

This is my first post do please excuse me if there any mistakes in my question. I have a skywatcher 200pds and I currently have the 10mm super plossl eyepiece. I was looking into getting more eyepiece in the 25-30mm range and also in the 4-10mm range. I am really confused with the different types, ethos, orthos.. Nagler...explore scientific etc.. I am really confused. Is there any advantage of using one type over other? Are some of them old types.. Any help would be greatly appreciated. It will help clear some cloud over this topic.

Thanks again in advance for all your help

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I'd start by asking your budget before getting into specific brands and types.

Generically, the different types yield

  1. Different apparent fields of view (how wide it looks inside the eyepiece) with wider costing more, in general.
  2. Different eye reliefs (how close you have to be so see the entire apparent field of view).  Again, more costs more.  If you have strong astigmatism in your eye, you'll need longer eye relief.
  3. Varying levels of edge correction (how pinpoint sharp does something in the center remain as its moved to the edge).  Again, sharper at the edge costs more.
  4. Varying physical sizes (which are dependent upon the above).  Smaller can sometimes cost more because more expensive glass has to be used.

There are more variables, but those are the ones talked about here the most.

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Plossls tend to be the generic eyepieces given with most scopes these day. They tend to be cheap and of variable quality. Nagler and Ethos are much a much higher range of EP’s of a much better quality and give better views, but with a substantial increases in the cost of them though. A single Nagler EP would cost considerably more than what you paid for your scope, and whilst it would be a great EP, with good views to go along with it, you need first off to work out a budget for your EPs, and find the best ones for that budget. Unless you are filthy rich of course and money is no object then you can ignore that advice altogether! ;) 

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13 hours ago, Louis D said:

I'd start by asking your budget before getting into specific brands and types.

Generically, the different types yield

  1. Different apparent fields of view (how wide it looks inside the eyepiece) with wider costing more, in general.
  2. Different eye reliefs (how close you have to be so see the entire apparent field of view).  Again, more costs more.  If you have strong astigmatism in your eye, you'll need longer eye relief.
  3. Varying levels of edge correction (how pinpoint sharp does something in the center remain as its moved to the edge).  Again, sharper at the edge costs more.
  4. Varying physical sizes (which are dependent upon the above).  Smaller can sometimes cost more because more expensive glass has to be used.

There are more variables, but those are the ones talked about here the most.

Hi

Thanks for taking the time to reply. I have a decent budget. I can spare around 100 for a good eyepiece. But I don't mind if there are good ones coming in at lower cost as well. What I am after is what is value for money in peoples opinion to use on a Skywatcher 200pds. My aim is to take pictures using this scope. However, I would like to look at objects as well. I can go and buy the 28mm skywatcher LET eyepiece. But, if I can put some more(not a lot) money and get a decent eyepiece I would like to explore the options. This is where I stumbled on so many names that I got confused. 

Thanks!

 

 

 

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12 hours ago, Knighty2112 said:

Plossls tend to be the generic eyepieces given with most scopes these day. They tend to be cheap and of variable quality. Nagler and Ethos are much a much higher range of EP’s of a much better quality and give better views, but with a substantial increases in the cost of them though. A single Nagler EP would cost considerably more than what you paid for your scope, and whilst it would be a great EP, with good views to go along with it, you need first off to work out a budget for your EPs, and find the best ones for that budget. Unless you are filthy rich of course and money is no object then you can ignore that advice altogether! ;) 

Thanks for you reply. That is what I have gathered. As I said in my previous reply, I can spare 100 on a good eyepiece. All these terms Nagler, Ethos, Orthos..etc.. Is there any advantage of one over the other. Any pros and cons of each. There are other EP which I came across i.e the explore scientific 100 degree  and they cost a fortune. What types are they ?

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Posted (edited)

Hi Yogesh, and welcome to the forum.  Explore Scientific is a good make with an excellent reputation, the following ep's are within your price range (the eye relief on the higher mags is a little short if you wear spectacles):
https://www.firstlightoptics.com/explore-scientific-eyepieces/explore-scientific-62-series-ler-eyepieces.html
If you want something a bit cheaper then the following are very good and highly recommended (the eye relief on these is consistently good, about 16mm, ok for spectacle wearers):
https://www.firstlightoptics.com/bst-starguider-eyepieces.html

Edited by rwilkey
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On 04/06/2018 at 12:52, rwilkey said:

Hi Yogesh, and welcome to the forum.  Explore Scientific is a good make with an excellent reputation, the following ep's are within your price range (the eye relief on the higher mags is a little short if you wear spectacles):
https://www.firstlightoptics.com/explore-scientific-eyepieces/explore-scientific-62-series-ler-eyepieces.html
If you want something a bit cheaper then the following are very good and highly recommended (the eye relief on these is consistently good, about 16mm, ok for spectacle wearers):
https://www.firstlightoptics.com/bst-starguider-eyepieces.html

HI rwilkey,

Thanks for taking the time to reply. Sorry for replying back late but I was caught up in some personal stuff. Thanks for giving those links I will have  a look and try and get some decent eyepiece. Also, want to get a Barlow but can't make up my mind between 2, 3 or 5x. This will be for taking images of the planets. 

One question though, is there some information on different types of eyepiece and how they differ amongst each other?

 

Thanks again! 

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22 minutes ago, Yogesh said:

HI rwilkey,

Thanks for taking the time to reply. Sorry for replying back late but I was caught up in some personal stuff. Thanks for giving those links I will have  a look and try and get some decent eyepiece. Also, want to get a Barlow but can't make up my mind between 2, 3 or 5x. This will be for taking images of the planets. 

One question though, is there some information on different types of eyepiece and how they differ amongst each other?

 

Thanks again! 

Your 200P (1200mm focal length) can give good visual results from quality mid-range eyepieces. I recommend trying a Vixen SLV - that range goes from 2.5mm to 25mm. Vixen also make a 2x Barlow & 8 to 24mm zoom (LV). https://www.firstlightoptics.com/vixen-eyepieces/vixen-slv-eyepieces.html

So for 100x a 12mm, 50x a 25mm. All the magnifications as shown below.

 

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45 minutes ago, Yogesh said:

HI rwilkey,

Thanks for taking the time to reply. Sorry for replying back late but I was caught up in some personal stuff. Thanks for giving those links I will have  a look and try and get some decent eyepiece. Also, want to get a Barlow but can't make up my mind between 2, 3 or 5x. This will be for taking images of the planets. 

One question though, is there some information on different types of eyepiece and how they differ amongst each other?

 

Thanks again! 

Hi,

This piece was written by Robin (rwilkey) and is a good "primer" on eyepieces:

http://www.swindonstargazers.com/beginners/eyepieces.htm

It probably seems a complex topic and thats because it is !. There is so much choice in eyepieces these days, it can be bewildering.

We all have our favourites but a guide like Robins is worth a read because it covers the characteristics that the different designs have and their plusses and minuses in a very balanced way.

 

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Posted (edited)

.......ditto the swindon link, my eyepiece collection is  mostly based on  information gleaned from that site.

I've  had some good eyepieces and feel more comfortable using the eyepieces, presently listed in my signature, the 'better' ones have gone! but better for who? You don't/wont know until you try!

Also between rwilkey and John, both are well versed in their knowledge of eyepieces, but only you will know whats best for your needs. Some of my sold items were/came highly recommended, but there's more to it than just sticking an eyepiece in the end of the scope? Conditions, user ability, telescope quality and ability all go to make for a better situation. Finding the right combination, thats all that matters. 

Edited by Charic

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On 06/06/2018 at 18:28, 25585 said:

Your 200P (1200mm focal length) can give good visual results from quality mid-range eyepieces. I recommend trying a Vixen SLV - that range goes from 2.5mm to 25mm. Vixen also make a 2x Barlow & 8 to 24mm zoom (LV). https://www.firstlightoptics.com/vixen-eyepieces/vixen-slv-eyepieces.html

So for 100x a 12mm, 50x a 25mm. All the magnifications as shown below.

 

Thanks for your reply. Appreciate you taking out time to post links for the eyepiece. I will certainly have a look at those. My telescope which is a 200PDS has 1000mm focal length. The eyepieces will still hold good right?

 

 

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On 06/06/2018 at 18:37, John said:

Hi,

This piece was written by Robin (rwilkey) and is a good "primer" on eyepieces:

http://www.swindonstargazers.com/beginners/eyepieces.htm

It probably seems a complex topic and thats because it is !. There is so much choice in eyepieces these days, it can be bewildering.

We all have our favourites but a guide like Robins is worth a read because it covers the characteristics that the different designs have and their plusses and minuses in a very balanced way.

 

I did not know rwilkey had such an amazing article on the eyepieces section. I haven't read it completely but I was looking at that website in general and it has such wealth of information. Thanks a lot Robin (rwilkey) for writing those. It is because of such articles that newbies like me benefit. 

Another thing that I would like to ask relating to eyepiece.  I had borrowed a 28mm 2" Eyepiece from a friend the skywatcher one I had trouble focusing with it if I just used the 2" eyepiece inserted directly in the focuser. So I had to hold the some length outside the focuser to get a good image. It was a bit weird because I was now holding the eyepiece in hand and trying to get focus. Also, The 10mm eyepiece that came with the scope could not focus if I just used it on its own. I had to use and extension which I made by removing the lens from a cheap celestron barlow that I had and used it. It still puzzles me that the eyepiece couldn't focus right out of the box. Also, I must admit that I have got a used telescope which is in a very good state. So, the question is do I have to use different extension tubes with different eyepiece ? Also, does skywatcher 200PDS come with any extension tubes in the box ? 


Thanks again for the replies. I am learning so much by joining this forum.

 

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On 06/06/2018 at 18:48, Charic said:

.......ditto the swindon link, my eyepiece collection is  mostly based on  information gleaned from that site.

I've  had some good eyepieces and feel more comfortable using the eyepieces, presently listed in my signature, the 'better' ones have gone! but better for who? You don't/wont know until you try!

Also between rwilkey and John, both are well versed in their knowledge of eyepieces, but only you will know whats best for your needs. Some of my sold items were/came highly recommended, but there's more to it than just sticking an eyepiece in the end of the scope? Conditions, user ability, telescope quality and ability all go to make for a better situation. Finding the right combination, thats all that matters. 

Thanks Charic for replying. I hope to soon have a decent collection of my own as well. 

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I have some I bought new and some from here second hand, each is a different model if not brand as I want to try different styles and designs.

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1 hour ago, Yogesh said:

I did not know rwilkey had such an amazing article on the eyepieces section. I haven't read it completely but I was looking at that website in general and it has such wealth of information. Thanks a lot Robin (rwilkey) for writing those. It is because of such articles that newbies like me benefit. 

Another thing that I would like to ask relating to eyepiece.  I had borrowed a 28mm 2" Eyepiece from a friend the skywatcher one I had trouble focusing with it if I just used the 2" eyepiece inserted directly in the focuser. So I had to hold the some length outside the focuser to get a good image. It was a bit weird because I was now holding the eyepiece in hand and trying to get focus. Also, The 10mm eyepiece that came with the scope could not focus if I just used it on its own. I had to use and extension which I made by removing the lens from a cheap celestron barlow that I had and used it. It still puzzles me that the eyepiece couldn't focus right out of the box. Also, I must admit that I have got a used telescope which is in a very good state. So, the question is do I have to use different extension tubes with different eyepiece ? Also, does skywatcher 200PDS come with any extension tubes in the box ? 


Thanks again for the replies. I am learning so much by joining this forum.

 

According to this SGL posting, it's supposed to come with two extension tubes, one 2" and one 1.25".  Perhaps you're missing one or both.  Did you buy new or used?

They're necessary because the PDS is setup to have adequate backfocus for DSLR usage.  This necessitates raising the eyepiece position to that of a DSLR imaging chip.  The extension tubes are not used with DSLRs.

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48 minutes ago, Louis D said:

According to this SGL posting, it's supposed to come with two extension tubes, one 2" and one 1.25".  Perhaps you're missing one or both.  Did you buy new or used?

They're necessary because the PDS is setup to have adequate backfocus for DSLR usage.  This necessitates raising the eyepiece position to that of a DSLR imaging chip.  The extension tubes are not used with DSLRs.

Hi Louis,

Thanks for replying back. I did buy a used one so, that would explain. I tried searching on First light optics website but could not find them. A quick search on google also does not yield anything. Is it possible you could help me with this ?

Thanks again!

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Hi Yogesh, here is a site for you for extension tubes but you will need to be careful in getting the right one, what you will need to do is measure (somehow) the distance of outward travel you need in mm and go from there, if it's slightly over then this will be OK as you can then rack it in.  The following supplier has a good return policy and I have used them and returned the odd item, so if your extension does not meet your criteria I am sure they would change it, if you get a 2" one (for your 28mm) you will also get a 1.25" adaptor to use as well, so here is the link:
https://www.telescopehouse.com/accessories/eyepiece-adaptors-and-extension-tubes.html

The choices seem to be the 35mm or the 50mm Revelations

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On 08/06/2018 at 18:18, rwilkey said:

Hi Yogesh, here is a site for you for extension tubes but you will need to be careful in getting the right one, what you will need to do is measure (somehow) the distance of outward travel you need in mm and go from there, if it's slightly over then this will be OK as you can then rack it in.  The following supplier has a good return policy and I have used them and returned the odd item, so if your extension does not meet your criteria I am sure they would change it, if you get a 2" one (for your 28mm) you will also get a 1.25" adaptor to use as well, so here is the link:
https://www.telescopehouse.com/accessories/eyepiece-adaptors-and-extension-tubes.html

The choices seem to be the 35mm or the 50mm Revelations

Hi Robin,

Thanks a lot for giving that link. I am thinking of getting the 50mm one. One question though, Is there some maths I can use to get the required length for the eyepiece to attain focus ?

Thanks again!

 

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I don't know much about this, but your question seems to cover both brands and types of eyepiece.

Plossls are the commonest type and work well as all round eyepieces, they use two doublet lenses back to back. The combination of simple design and good performance means they dominate at lower price points. They have replaced cheap Huygens lenses that use two plano convex lenses which don't correct abberations as well. The downside is the 'eye relief' gets less as they get 'stronger' which means they are increasingly difficult to use as you get to short focal lengths. I find my 4mm one almost impossible to use.

A Nagler is (I think) essentially a plossl with a built in barlow which shortens its overall focal length without reducing the eye relief and also have a wide field of view. By being an all-in one design the optics can be optimised over separate EP and Barlow so quality is generally very good, but big and heavy.

Orthoscopic eyepieces have excellent quality but a narrow field of view.

There are other types but I don't know enough about them to describe them.

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21 hours ago, Yogesh said:

Hi Robin,

Thanks a lot for giving that link. I am thinking of getting the 50mm one. One question though, Is there some maths I can use to get the required length for the eyepiece to attain focus ?

Thanks again!

 

Hi Yogesh, no, I have never come across any math for this calculation, the subject varies with each individual ep.

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The OP's 200PDS is a 1000mm focal length.

This eyepiece calculator:

http://telescope.eyepiece-calculator.co.uk/

Says the revelation 50mm will give a 10mm exit pupil. That's absolutely huge so you won't be able to see most of the view and will waste a lot of photons, making the view much dimmer than it beeds to be.

The 42mm gives an 8.2mm exit pupil, and will give brighter views if you are youngster (typically with 7mm eye pupils) without losing the 'immersive' effect.

The 30mm will give a 6mm exit pupil (ideal for older astronomers!)

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2 hours ago, Stub Mandrel said:

Says the revelation 50mm will give a 10mm exit pupil. That's absolutely huge so you won't be able to see most of the view and will waste a lot of photons, making the view much dimmer than it beeds to be.

Have you actually tried this with a 50mm and a 40mm of the same TFOV to see if the view is noticeably dimmer with the 50mm despite the larger exit pupil?  I would think extended objects like nebula would have higher per unit surface brightness due to compressing of the image into a smaller area.  Perhaps your iris will attenuate the gain and it won't be any brighter than at 40mm, but I wouldn't expect it to actually be dimmer on a per unit area basis.  I would believe that secondary shadow starts to become a real issue below 40mm with that scope, especially when viewing the moon.

You should be able to see the entire AFOV at 50mm, it's just that due to pupil mismatch, lots of photons will hit your iris instead of your retina as you say, but the AFOV remains the same.

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I'm just passing on what I was told when I asked a similar question!

Some people say a big exit pupil gives a wider view.

But surely AFOV fits into the exit pupil, so to see all around it you would need to move your eye position?

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Posted (edited)

Exit pupil is only loosely related to field of view. Instead it is the width of the beams of light coming out of an eyepiece. So a star goes down the telescope tube as a beam 100mm wide (assuming 10cm aperture) and comes out as a beam (exit pupil) 1mm wide (assuming 100x magnification). At lower magnification (and hence wider TFOV) the exit pupil is larger. In my example 25x mag would give 4mm exit pupil. At 10x mag the beam is 10mm wide - too wide to fit through your eye's pupil.

Edited by Ags

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3 hours ago, Stub Mandrel said:

Some people say a big exit pupil gives a wider view.

Because big exit pupils are associated with long focal length eyepieces, you'll generally get a wide true field of view.  However, the eyepiece could have a very restrictive field stop and negate that possibility.

3 hours ago, Stub Mandrel said:

But surely AFOV fits into the exit pupil, so to see all around it you would need to move your eye position?

If you focus on a close object like a tree, you can see parallax shift with large exit pupils as you move your eye around within the exit pupil because you're picking up different bundles of light coming in through different parts of the objective.  However, the true field of view remains the same (to a first order approximation).

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