ICEINSPACE
Most Read Articles
Moon Phase
CURRENT MOON Waxing Gibbous
80.8%
The Sun Now
Time Zones
Sydney
12:24 am
Perth
10:24 pm
Auckland
2:24 am
New York*
10:24 am
Paris*
4:24 pm
GMT
2:24 pm




  #1  
Old 02-01-2018, 04:53 PM
anaxa (Syd)
Registered User

anaxa is offline
 
Join Date: Dec 2017
Location: Beachmere ,Queensland
Posts: 8
Hyperion

Hi all,
What is the general consensus on the Hyperion eyepieces?
I have just added the 17mm to my collection but due to poor weather have not been able to test it yet.
I also have got the extension tubes with it. I think it goes that when the 14mm is in the eyepiece goes to a 10mm.And when the 28mm is in it goes to a 5mm but not clear on that. I wonder what it goes to when you use both extension together?
I have also got the attachment ring system to put my dslr directly to the eyepiece.
Has anybody used a dslr in this way rather then as a prime?
The other interesting thing on this eyepiece is it can be used with a dslr lens in between the dslr body and the eyepiece.
Has any of you learned ladies and gentleman done any work on this?


Regards Syd.
Reply With Quote
  #2  
Old 02-01-2018, 05:56 PM
GeoffW1's Avatar
GeoffW1 (Geoff)
Registered User

GeoffW1 is offline
 
Join Date: Sep 2006
Location: Sydney
Posts: 1,838
Hi,

I have a set of these and like them a lot. I think they are a good balance between price, quality and FOV. I have the extension rings too. I don't use them every night but they are good when needed. I have a 200mm SCT, but some other scopes aren't suited so well.

Alex has a few comments on these EPs well worth reading. He is more discerning than me (or picky, eh, eh?)

http://www.iceinspace.com.au/forum/s...archid=4197085

Cheers
Reply With Quote
  #3  
Old 02-01-2018, 07:41 PM
Wavytone
BigBanger

Wavytone is offline
 
Join Date: Jul 2008
Location: Killara, Sydney
Posts: 2,947
Well of course they suit an SCT - the field curvature is a fair match for that of the SCT which is concave towards the sky, like a refractor. And Alex does have an SCT as well as several dobs.

As he said he has a fair collection of eyepieces that has evolved to some extent by "suck and see, flog what doesn't work", as well as trying those I've had over the years.

Eyepieces should be matched to your scope AND the observer. There is no single "best eyepiece" for all scopes/observers.

The hardest part is that manufacturers do not disclose the field curvature of the eyepiece, nor its off-axis correction (monochromatic aberrations as well as lateral colour).

For example its pretty clear Televue eyepieces designed to suit dobsonians - the main market in the US, whereas in Japan and Europe most scopes are refractors 80-130mm aperture. If they at least disclosed the field curvature this would be a huge help. You can see this on Cloudynights (predominately US users) where the answers to almost every question are (a) buy a big dob, and (b) buy a clutch of TV eyepieces.

Vixen's eyepieces OTOH were aimed primarily at refractors (and suit Maks and SCTs too), though the LVW design is quite old - older than TV Naglers BTW. The LVW series were rebranded, mainly by Orion.

FWIW Hyperions were an inferior copy of the LVW series, though popular because of lower cost than the LVWs; as are the cheaper Stratus (also inferior).

Last edited by Wavytone; 02-01-2018 at 07:57 PM.
Reply With Quote
  #4  
Old 02-01-2018, 09:51 PM
bigjoe (Joe)
Registered User

bigjoe is offline
 
Join Date: Nov 2010
Location: sydney
Posts: 1,143
Quote:
Originally Posted by GeoffW1 View Post
Hi,

I have a set of these and like them a lot. I think they are a good balance between price, quality and FOV. I have the extension rings too. I don't use them every night but they are good when needed. I have a 200mm SCT, but some other scopes aren't suited so well.

Alex has a few comments on these EPs well worth reading. He is more discerning than me (or picky, eh, eh?)

http://www.iceinspace.com.au/forum/s...archid=4197085

Cheers
Geoff , these do indeed produce a nice clear sharp image in the right scope as Alex and Wavy state ..Ive not tried their extension rings, and no longer have some Hyperions...only Televue , some Orthos and some TS Dual Eds ( nice surprise ) few others .
bigjoe
Reply With Quote
  #5  
Old 03-01-2018, 12:01 PM
anaxa (Syd)
Registered User

anaxa is offline
 
Join Date: Dec 2017
Location: Beachmere ,Queensland
Posts: 8
Hyperion

Glad to note they are suited to a SCT.
I have a Meade LX80 200mm running a 50mm eyepiece set with it.
Interesting comment about the curvature match to the scope .
I would have thought at the distances being observed that would not have been an issue.
The further out you go the flatter the field.
Anyway thank you all for the comments, it has led me to the next question.
If money was not an issue what would the best eyepiece set to get?

Regards Syd.
Reply With Quote
  #6  
Old 03-01-2018, 01:53 PM
bigjoe (Joe)
Registered User

bigjoe is offline
 
Join Date: Nov 2010
Location: sydney
Posts: 1,143
Quote:
Originally Posted by anaxa View Post
Glad to note they are suited to a SCT.
I have a Meade LX80 200mm running a 50mm eyepiece set with it.
Interesting comment about the curvature match to the scope .
I would have thought at the distances being observed that would not have been an issue.
The further out you go the flatter the field.
Anyway thank you all for the comments, it has led me to the next question.
If money was not an issue what would the best eyepiece set to get?

Regards Syd.
Syd there is some variation in optically quality in some EP sets ...eg Nagler type 6s the best to me and some others were the 13mm, 9mm ,16mm and 5mm..others all very good but the 13mm is simply amazing in a SCT , as are a 19mm and 24mm Pan..
Some Vixens and Tak LEs and most of the ES 68 range , Dual Eds from TS , Astrotech , Agena etc look very good below 18 mm in SCTs and at a very low price..So no real need to spend big.

Really a lot is trial and error for your scope at times .. You need to look back on EP posts, and there comments to see what suits the curvature of your scope.
PS :All the Deloi Ive had perform great in Any scope Ive put them in!
bigjoe.

Last edited by bigjoe; 03-01-2018 at 02:12 PM. Reason: Add
Reply With Quote
  #7  
Old 03-01-2018, 06:05 PM
anaxa (Syd)
Registered User

anaxa is offline
 
Join Date: Dec 2017
Location: Beachmere ,Queensland
Posts: 8
Hi Joe,
Whats your opinion of the Meade 4000 or 6000 series sets.
Reply With Quote
  #8  
Old 03-01-2018, 06:08 PM
anaxa (Syd)
Registered User

anaxa is offline
 
Join Date: Dec 2017
Location: Beachmere ,Queensland
Posts: 8
Geoff,love the quote on your message.

Regards Syd.
Reply With Quote
  #9  
Old 03-01-2018, 06:36 PM
bigjoe (Joe)
Registered User

bigjoe is offline
 
Join Date: Nov 2010
Location: sydney
Posts: 1,143
Quote:
Originally Posted by anaxa View Post
Hi Joe,
Whats your opinion of the Meade 4000 or 6000 series sets.
The series 4000s that I had , and came with some scopes from Meade , were to me in every instance not as good as the GSO plossls in a variety of scopes..only good one was their 26mm.. The 9mm GSO was excellent.. The 12 and 18mm Meade HDs I had, not as good to me as the Agena /TS
Dual EDs (very unfashionable or underrated ..I dont know) .

If it were me starting out, and to save money Id just get the EDs to 15mm and a 24mm Pan(barlows very well).
bigjoe.

Last edited by bigjoe; 03-01-2018 at 06:39 PM. Reason: Adding
Reply With Quote
  #10  
Old 04-01-2018, 02:45 PM
anaxa (Syd)
Registered User

anaxa is offline
 
Join Date: Dec 2017
Location: Beachmere ,Queensland
Posts: 8
Thank you Joe,
I will take your advice and go that road.
One problem I have is poor eye sight from childhood.
So I generally look for large FOV and not to much mag as my tripod is an EQ6 and not that well made.

Anyway thank you for your help.

Regards Syd
Reply With Quote
  #11  
Old 04-01-2018, 03:16 PM
bigjoe (Joe)
Registered User

bigjoe is offline
 
Join Date: Nov 2010
Location: sydney
Posts: 1,143
Quote:
Originally Posted by anaxa View Post
Thank you Joe,
I will take your advice and go that road.
One problem I have is poor eye sight from childhood.
So I generally look for large FOV and not to much mag as my tripod is an EQ6 and not that well made.

Anyway thank you for your help.

Regards Syd
Your most welcome ..thats what were here for ..to share our knowledge and experience, so that others may benefit , and maybe not make the expensive mistakes , that can so easily happen in Astro.
bigjoe.
Reply With Quote
  #12  
Old 05-01-2018, 11:18 AM
dannat's Avatar
dannat (Daniel)
daniel

dannat is offline
 
Join Date: Sep 2007
Location: Macedon shire, Australia
Posts: 3,355
i found the hyperion a bit heavy & over-priced for what you can buy elsewhere four under $100, th meade HD, BST explorer/astrotech paradigm are better value imo, baader didn't catch up or change anything when many of the sub 100 60 deg ep's showed up
Reply With Quote
  #13  
Old 05-01-2018, 04:12 PM
bigjoe (Joe)
Registered User

bigjoe is offline
 
Join Date: Nov 2010
Location: sydney
Posts: 1,143
Quote:
Originally Posted by dannat View Post
i found the hyperion a bit heavy & over-priced for what you can buy elsewhere four under $100, th meade HD, BST explorer/astrotech paradigm are better value imo, baader didn't catch up or change anything when many of the sub 100 60 deg ep's showed up
Coudnt agree more with this Dan ..The Dual EDs with any Label , are an outstanding Price versus Optical Quality buy.
Can you get better... of course ; but not by a whole lot. IMO.
bigjoe


bigjoe.

Last edited by bigjoe; 05-01-2018 at 04:38 PM. Reason: Add
Reply With Quote
  #14  
Old 08-01-2018, 06:47 PM
Tasastro (Bill)
Registered User

Tasastro is offline
 
Join Date: Apr 2017
Location: Tasmania
Posts: 26
Quote:
Originally Posted by Wavytone View Post
Well of course they suit an SCT - the field curvature is a fair match for that of the SCT which is concave towards the sky, like a refractor. And Alex does have an SCT as well as several dobs.
There is rumour going round the amateur astronomy community that the focal surface curvature relative to the eyepiece of Newtonians is opposite to that of other telescope types. Because of this certain eyepieces are reputed to work best with refractors or SCT's and others are more suited to Newtonians. It's an interesting theory but unfortunately only partially true in general and quite incorrect in one fact - the focal surface curvature direction relative to the eyepiece is the same for nearly all telescope types.

In anticipation of the storm of protest from the resident experts I could quote a number of supporting references but will use only Rutten and Van Venrooij, Telescope Optics here. Anyone who wishes to gain some understanding of the interaction between telescope objectives and eyepieces should read the whole book but particularly Chapter 16, Eyepieces for Telescopes.

Under the sub-heading The Performance of Objective-Eyepiece Combinations, on page 181 they quote "Between the tangential and sagittal focal surfaces lies the average curved field, a somewhat imaginary construct. For most objectives -- refractors, Newtonians, and Cassegrain-like systems this surface is inward curving", by which they mean convex towards the eyepiece (or "concave towards the sky" as Wavytone puts it).

The origin of the myth lies in an incomplete understanding of raytracing and particularly the surface curvature conventions. In optical specifications and ray-tracing results, focal surfaces for SCT's and other Cassegrains, and refractors all have negative sign, those for Newtonians are nearly always positive*, but it is wrong to conclude from this that curvatures relative to the eyepieces are opposite.

To quote Rutten et al again:
Chapter 20 Optical Calculations sub-heading 20.4 Sign Conventions on page 240:
"Light entering the optical system travels from left to right.
Distances from left to right are signed positive; those from right to left, negative.
Curvatures with the convex side to the left are signed positive; otherwise they are negative."

For refractors and Cassegrain-like types the rays approach the focal surface from the left and the focal surface has a negative sign ie convex to the right and towards the eyepiece.

For Newtonians the rays approach the focal surface from the right
(the diagonal mirror is ignored - it has no optical power and turning the rays at right angles is not regarded as changing their direction). The focal surface has a positive sign ie convex to the left and towards the eyepiece.

The interactions between eyepiece and objective are quite complex and involve a combination of astigmatism and field curvature with the former being usually dominant. Certain eyepieces will work better or worse with different telescopes but it does not depend only on the type of optical system. Again - read Rutten and Van Venrooij if you want to go some way towards understanding how it all works.

* There are of course some exceptions - Maksutov Newtonians have a focal surface that is convex away from the eyepiece ie. a negative sign of the focal surface radius.

Last edited by Tasastro; 10-01-2018 at 06:18 PM. Reason: spelling and grammar corrections, addendum
Reply With Quote
  #15  
Old 08-01-2018, 10:12 PM
Wavytone
BigBanger

Wavytone is offline
 
Join Date: Jul 2008
Location: Killara, Sydney
Posts: 2,947
Suggest you check http://www.telescope-optics.net/curvature.htm for the telescope types in question the aberrations are analytic to 3rd order at least from the Petzval sum.

Field curvature for refractors and 1 or 2 mirror systems is shown on the above page. The figure in the middle of the page quite nicely shows the situation for refractors vs Newtonians.

There is also a simple reason why this is the case - a simple doublet lens has a focal length that is almost constant as a point object (ie a star) as the object moves off axis the image of it must move in an arc - if it followed a flat plane the focal length must increase with the off-axis angle - which it doesn't - not for a doublet. The whole need for image flatteners arises from this.

For a Newtonian the simplest case is a spherical mirror - lets take a 6" f/8 for example which is near enough to parabolic to not matter. The spherical surface is symmetric about the centre of the sphere which means that if the primary is rotated about the centre to one side, the image MUST lie on a sphere of radius R/2 concentric with the centre of the primary spherical surface, ie concave towards an eyepiece and exactly as shown in the figure.

NOTE: Refractor = convex toward eyepiece, Newtonian = concave towards eyepiece. So in other words an eyepiece that suits one is not a great match for the other.

In a maksutov the field curvature is essentially determined by the two mirror radii, see http://telescope-optics.net/MCT_off_axis.htm equation 133. Note the concluding remark: " fairly accurate estimate of the median image curvature in an MCT, in a typical system it can be expected to be numerically quite close to the secondary mirror radius of curvature."

It is also convex towards the eyepiece (same as for a refractor) because the Maksutov design is effectively spherically symmetric around the centre of curvature of the primary mirror - which you should know if you have a copy of Maksutovs original article or S&T Gleanings Bulletin C.

In an SCT field curvature is not affected by the corrector (zero power) and hence it is determined again as the petzval sum due to the mirrors and once again is similar to that of a refractor ie convex towards the eyepiece. http://www.telescope-optics.net/SCT_...berrations.htm

See also http://www.hnsky.org/LX200_optical_analysis.htm

Consequently a field flattener made for a refractor or SCT will not work in a Newtonian, and vice versa.

Last edited by Wavytone; 09-01-2018 at 10:35 AM.
Reply With Quote
  #16  
Old 09-01-2018, 11:23 AM
Tasastro (Bill)
Registered User

Tasastro is offline
 
Join Date: Apr 2017
Location: Tasmania
Posts: 26
Quote:
Originally Posted by Wavytone View Post
Suggest you check http://www.telescope-optics.net/curvature.htm for the telescope types in question the aberrations are analytic to 3rd order at least from the Petzval sum.

Field curvature for refractors and 1 or 2 mirror systems is shown on the above page. The figure in the middle of the page quite nicely shows the situation for refractors vs Newtonians.

There is also a simple reason why this is the case - a simple doublet lens has a focal length that is almost constant as a point object (ie a star) as the object moves off axis the image of it must move in an arc - if it followed a flat plane the focal length must increase with the off-axis angle - which it doesn't - not for a doublet. The whole need for image flatteners arises from this.

For a Newtonian the simplest case is a spherical mirror - lets take a 6" f/8 for example which is near enough to parabolic to not matter. The spherical surface is symmetric about the centre of the sphere which means that if the primary is rotated about the centre to one side, the image MUST lie on a sphere of radius R/2 concentric with the centre of the primary spherical surface, ie concave towards an eyepiece and exactly as shown in the figure.

NOTE: Refractor = convex toward eyepiece, Newtonian = concave towards eyepiece. So in other words an eyepiece that suits one is not a great match for the other.
I am pleased you quote telescope-optics.net in your attempt at refutation of my claim, I was considering using it as a supporting reference but thought the technical treatment might put people off.

Yes indeed the Petzval surface of a Newtonian is opposite to that of refractors and SCT's, however the actual field curvature only coincides with the the Petzval in the absence of astigmatism.
If you read further down the page you refer to, the author says: (my emphasis)

"As mentioned, the presence of astigmatism significantly alters the image field curvature properties. The Petzval surface becomes fictitious, and the actual best image surface becomes the one containing best astigmatic foci. Due to the longitudinal extension of astigmatism, this image is split into sagittal, tangential and best, or median image surface sandwiched in between the first two."

reading still further: (my emphasis)

"For a mirror of radius of curvature R with the stop at the surface, sagittal and tangential image curvatures, respectively, are given by:
which, with RP=R/2, can be written as 1/Rs=0 (implying Rs= ∞), and 1/Rt=-4/R. The median image surface, given by Eq. 33 as one half of the sum of sagittal and tangential curvatures, is 1/Rm=-2/R, equaling mirror focal length (as absolute value; the plus sign implies that it is concave toward mirror, for mirror oriented to the left). In other words, the median surface has the same curvature radius as the Petzval, but of opposite sign." .


All this confirms my contention (and every statement about this aspect of telescope objective field curvature by a reputable optician) : the actual focal surface for a Newtonian is convex towards the eyepiece like refractors and SCT's. This is nicely illustrated in figure 67 on the same page - the actual focal surface is m, between the tangential and saggittal surfaces.


If any further support is needed see http://www.telescope-optics.net/eyep...rrations_1.htm . This page gives an extremely good but rather technical treatment of the interaction between eyepiece and objective. Under the sub-heading Eyepiece Field Curvature the author states: (my emphasis)

"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 ...." - which in my opinion sums up this subject.

My last words on this subject are: the best eyepiece is the one you find works best with your telescope. Disregard blanket statements that a particular eyepiece only works well with a certain type of objective.









Last edited by Tasastro; 15-01-2018 at 07:33 PM. Reason: A few minor additions and small grammatical corrections
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 12:24 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Advertisement
NexDome Observatories
Advertisement
Atik Horizon
Advertisement
FLI Cameras and Imaging Accessories
Advertisement
SkyWatcher 2018 Catalogue
Advertisement
Lunatico Astronomical
Advertisement
Bintel
Advertisement
OzScopes Authorised Dealer
Advertisement
Interest Free Finance
Advertisement
SkyWatcher WiFi Adaptor
Advertisement
Astronomy and Electronics Centre
Advertisement