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cloudsweeper

Hyperion Aspheric 36/72 First Light

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This EP has aspheric elements for good optical correction since rays on- and off-axis reach the same focus.  This is achieved without the use of too many elements, thus keeping down cost, size, and weight.

It has a quality build, 20mm eye relief, large eye lens, and comes with an adaptor for a 1.25" diagonal (although this reduces the AFOV to 55 deg).

I bought it as an improvement on the Revelation 42/65, and as an occasional alternative the bulky (992g - balance issues, focuser slippage) ES 30/82.

The ST120 frac was used to compare these three EPs, since aberrations are emphasised in a fast 'scope.   In that 'scope, they all give low mag and a TFOV of more than 4 deg.

After a quick look at the lovely slender waxing crescent Moon, sinking behind trees, I aimed at the Pleiades.  Concentrating on the centre, I then moved the central stars to the edges, remembering to take my varifocals off since they give a different impression when looking at the top and bottom of the FOV!

FINDINGS

All three EPs gave sharp stars at the centre, and no field curvature in the central region where one's attention is mainly concentrated.

All three exhibited astigmatism at the field edge, worst in the case of the Revelation.

The exit pupil was large in all cases, so contrast would not be great, and any differences would perhaps be due to EP performance.  The contrast was poorest in the case of the Rev, with faint stars not showing so well.

(I also checked out my ES 24/68 and Meade 5000 20/82, and they too showed astigmatism.)

CONCLUSION

The Revelation Superview is without doubt a reasonable EP for the price.  The Hyperion is better, but the costlier ES is not noticeably better again as far as I could see in this simple test.

Doug.

 

P1060069.JPG

Edited by cloudsweeper
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I used to have the 31mm Aspheric in my C8 sct and really liked it. It is lightweight. Baader supply a strange fitting so you can cut this 2" eyepiece down to fit in 1.25" focuser (losing FOV !) - didn't see the point of that.

Then I got a Televue panoptic41. The background on the pan41 was so BLACK compared to the aspheric (even at a lower magnification!) that it revealed so many more stars.

I sold the Aspheric and loved the Panoptic instead. I am so fickle :) 

Then I met a Terminagler (Nagler 31) and the Panoptic 41 started to gather dust :) (and was sold :( )

(don't know how I am still with the wife :) )

Needless to say I now love the Ethos21 and the Nagler has been sold.

At least there is nowhere else to go! The end of the road has arrived...

Edited by alanjgreen
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Interesting test Doug.

As you've mentioned,  these are quit long fl EPs for f5, so there may some other factors than EP showing here, such

1. FC of the scope, with 600mm fl, I'd expect noticeable FC from it, have you tried to identify that?

2. 36mm hyperion, espiecially 42mm superview, might give larger exit pupil than your max pupil, the result will be aperture stop-down with long focal ratio, the less good transmission you felt can be compound result of some 15% lower mag and aperture stop-down.

3. Have you tried these EPs in C8? How's the field stops look like in C8? all clear defined? If so how's the field stops look like in 120frac? especially 36 and 42mm? if fuzzy, then you're likely to have aperture stop-down there.

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Good review. I find that even premium eyepieces start to show flaws in the optical path with a fast optics.

For example, The Ethos eyepiece is sharp to the edges in my 8SE but when using in the 14" 4.6 dob, when my collimation is only slightly out, the stars are slightly out of focus, more at one edge... basically when the secondary is not acatly 45 degrees. 

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Are you sure you have got the correct names for the different aberrations and distortions? I suspect when you say field curvature you mean pincushion distortion and when you say astigmatism you mean field curvature.

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53 minutes ago, YKSE said:

 

3. Have you tried these EPs in C8? How's the field stops look like in C8? all clear defined? If so how's the field stops look like in 120frac? especially 36 and 42mm? if fuzzy, then you're likely to have aperture stop-down there.

No - that's my next test.  I expect different performances in a slow 'scope!

D.

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14 minutes ago, Ricochet said:

Are you sure you have got the correct names for the different aberrations and distortions? I suspect when you say field curvature you mean pincushion distortion and when you say astigmatism you mean field curvature.

I didn't actually detect any FC.  Astigmatism tends to overwhelm it at the edges.  And astigmatism is unmistakable by its radial and tangential manifestations.

Doug.

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39 minutes ago, cloudsweeper said:

No - that's my next test.  I expect different performances in a slow 'scope!

D.

Well, standard SCT is a bit than a f10 newt, 8" sCT has FC slightly better than your 120f5, but none the less visible,  it has coma corresponding a f5.4 newt (if my memory doesn't fail me), so you're going to see coma/FC in the scope in combination of other aberrations in the EPs.

The field stop sharpness tests are more to have some idea wherearbout  is your max pupil, if all EP have sharp field stops in SCT. If  you have aperture stop-down in ST120, the field stop is cut by your eye pupil, which is not as clean cut as field stop in EPs, therefore it looks fuzzy.

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56 minutes ago, cloudsweeper said:

I didn't actually detect any FC.  Astigmatism tends to overwhelm it at the edges.  And astigmatism is unmistakable by its radial and tangential manifestations.

Doug.

What did the astigmatism look like?

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Nice review Doug. Be interested to see how the Aspheric and Explore Scientific compare in your 8SE SCT. I’ll keep an eye out for your next lot of tests. Cheers! :) 

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Interesting stuf Doug :smiley:

I bought a Hyperion Aspheric 36mm to use with a 6" F/12 refractor I had a while back. It was a nicely made eyepiece (as all Baader products seem to be) but I saw astigmatism at the field edges even at F/12, which was rather disappointing. They are light for 2" eyepieces though, on the plus side.

I'm not at all surprised that you found the ES 68 better corrected. I had the 24mm in that range and found it almost as good as the 24 Panoptic even in my F/5.3 dobsonian. Nice eyepiece for relatively good prices.

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On 1/20/2018 at 14:02, cloudsweeper said:

All three EPs gave sharp stars at the centre, and no field curvature in the central region where one's attention is mainly concentrated.

Generally, field curvature is only visible center to edge, so saying it's flat in the center isn't saying much at all.  Even my 30mm KK Widescan clone is flat of field in the central 50% despite having massive amounts of field curvature in the outer 50% relative to the center.

On 1/20/2018 at 14:02, cloudsweeper said:

Concentrating on the centre, I then moved the central stars to the edges, remembering to take my varifocals off since they give a different impression when looking at the top and bottom of the FOV!

Do you have no astigmatism in your eyes?  Is your cylinder (CYL) correction 0 diopters?  If not, you're going to see astigmatism in every eyepiece at that large exit pupil just from your eyes without correction.  That's why I have a dedicated pair of astronomy eyeglasses set to infinity focus and made from low dispersion material to correct my astigmatism at the eyepiece and to introduce as little edge chromatic aberrations as possible while doing it.  It also allows the entire field to be at the same focus at the same time.

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I did some ad hoc (terrestrial!) TESTS on my 31mm Baader Hyperion Aspheric.
I felt that (unlike other eyepieces) the abberations (whatever they were!) did
not get monotonically worse as the edge of the field was approached... It got
"worse, then better"? But such might be what I *expected* for an Aspheric? ;)

A distinct non-expert, but reviewing eyepieces ain't easy? (To be quantitative).
Distinguishing between the *precise* abberations isn't easy for *me* anyway!
I once imagined "Eyepiece Projection" might measure (image!) such things...
BUT that seemed to make things a whole lot worse for any real assessment! :p

Edited by Macavity

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1 hour ago, Louis D said:

Generally, field curvature is only visible center to edge, so saying it's flat in the center isn't saying much at all.  Even my 30mm KK Widescan clone is flat of field in the central 50% despite having massive amounts of field curvature in the outer 50% relative to the center.

But still worth saying anyway, I feel.  :happy11:

1 hour ago, Louis D said:

Do you have no astigmatism in your eyes?  Is your cylinder (CYL) correction 0 diopters?  If not, you're going to see astigmatism in every eyepiece at that large exit pupil just from your eyes without correction.  That's why I have a dedicated pair of astronomy eyeglasses set to infinity focus and made from low dispersion material to correct my astigmatism at the eyepiece and to introduce as little edge chromatic aberrations as possible while doing it.  It also allows the entire field to be at the same focus at the same time.

Next opportunity, I shall do a test with the f/10 'scope, and hopefully draw further conclusions.

As Chris says above, testing EP performance is not easy (because of all the factors that come into play).  But it's interesting to experiment anyway!  :happy10:

Doug.

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2 hours ago, Macavity said:

I once imagined "Eyepiece Projection" might measure (image!) such things...
BUT that seemed to make things a whole lot worse for any real assessment! :p

Not least of which is curvature of the projected image which a flat imager cannot tolerate at all, but most folks have no problem with a curved virtual image and never notice it.  This is different from having a curved focal plane at the field stop which many older folks can't accomodate.  I can only recall the Pentax XP line of eyepieces being specialized for eyepiece projection.  They had flat projected images and very tight eye relief.  I've also read of imagers making good use of microfiche projection lenses for eyepiece projection.

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Just taken the opportunity to further my tests by this time using the slow f/10 8SE (very little FC contributed).

EPs were: Rev Superview 42/65, Hyperion Aspheric 36/72, ES 30/82, Rev Superview 30/68, ES 24/68, and Meade 5000 UWA 20/82.

Conditions as before - Pleiades, specs removed (just in case!).

Personal judgement at the EP used of course, with the concomitant limitations there!

Contrast with the Rev 42 was poorest, but was similar for the others, perhaps to a large extent because the exit pupil was greatest with that Rev.

Sharpness in the central region was good in all cases, as expected.

But the big difference was with astigmatism.  (All EPs showed this with the f/5 frac, which firmly confirmed that fast 'scopes really test EPs!)

Rev 42 - astigmatism very noticeable at the edges.

Aspheric 36 - mostly FC, with just a hint of astig - there were wide ellipses either side of best focus rather than thinner lines which I saw before.

ES 30 - perhaps a bit less FC, but NO astig. - the defocused image was circular (with a darkened centre).

Rev 30 - mostly FC, with a hint of astig.

ES 24 - little FC, NO astig.

Meade 20 - again, little FC, NO astig.

CONCLUSIONS:

The widefield Revs performed most poorly, but I still think they are very good for their cost.

The big Meade and both the ES EPs were very good, with no astigmatism that I could detect.

So what about the Aspheric which I bought to replace the Rev 42, and as a convenient alternative the big ES 30/82?  Well, I found it very good, with just a hint of astigmatism, so Yes, it was a worthwhile purchase!  But I don't think I'll part with that big ES however - it is indeed a great (yet weighty) EP.

Doug.

 

 

 

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On 20/01/2018 at 21:10, alanjgreen said:

I used to have the 31mm Aspheric in my C8 sct and really liked it. It is lightweight. Baader supply a strange fitting so you can cut this 2" eyepiece down to fit in 1.25" focuser (losing FOV !) - didn't see the point of that.

Then I got a Televue panoptic41. The background on the pan41 was so BLACK compared to the aspheric (even at a lower magnification!) that it revealed so many more stars.

I sold the Aspheric and loved the Panoptic instead. I am so fickle :) 

Then I met a Terminagler (Nagler 31) and the Panoptic 41 started to gather dust :) (and was sold :( )

(don't know how I am still with the wife :) )

Needless to say I now love the Ethos21 and the Nagler has been sold.

At least there is nowhere else to go! The end of the road has arrived...

 

Good post that shows the journey that myself and many others have been on.  It’s expensive buying and selling (less so of course if buying second hand) but in the long run it could save money by spending big earlier, and enjoying great performance sooner. Especially relevant for short focal ratio scope users, less so for F8 or slower.

As as always, easy with hindsight.....

Ed.

 

 

 

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11 hours ago, Ricochet said:

Did you find out what your cyl values are? 

Afraid not! 

EP testing/comparison is a bit of a minefield, depending on the EPs of course, the 'scope(s) used, the observer's eyes and his/her perception (subjective response).

In terms of my own astigmatism (if any), I would think that it did not play a large part in my findings, since there was no consistency in observed astigmatic effects.

The experiences of other observers on this forum are of course invaluable on the learning path!

Doug.

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Update:

Finally managed to find my prescription, which states I have only very mild astigmatism - 0.5D. 

So - hopefully! - my findings without wearing specs are reasonably valid, particularly in view of the fact that the astig. I saw was not uniform and was in some instances absent.

As for testing with varifocals on, I would imagine looking at the TOP of the field edge would be advisable since that part of the lens is designed for distance, as opposed to the bottom part which is for close work.

Doug.

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48 minutes ago, cloudsweeper said:

Update:

Finally managed to find my prescription, which states I have only very mild astigmatism - 0.5D. 

So - hopefully! - my findings without wearing specs are reasonably valid, particularly in view of the fact that the astig. I saw was not uniform and was in some instances absent.

As for testing with varifocals on, I would imagine looking at the TOP of the field edge would be advisable since that part of the lens is designed for distance, as opposed to the bottom part which is for close work.

Doug.

Looking at your reports I guessed you would have astigmatism of 0.5 or slightly higher, which means that you will see astigmatism from your eye at exit pupils of 4mm or more. This explains why you saw it in every eyepiece in the f5 scope but not the f10. 

DioptrixAstigmatismVis.gif

http://www.televue.com/engine/TV3b_page.asp?id=54&Tab=_Choose

I can't imagine that using varifocals at the eyepiece will be much fun, probably better to get an additional pair of glasses but then there might be eye relief issues. 

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Thanks for that @Ricochet - very instructive!

My conclusions seem OK with the 8SE then, although it is less demanding of the EPs.

I generally prefer not to use specs at the EP, but it is easier to keep them for doing other things as well.  Not really a problem, as long there is enough eye relief of course.

Doug.

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8 hours ago, cloudsweeper said:

I generally prefer not to use specs at the EP, but it is easier to keep them for doing other things as well.  Not really a problem, as long there is enough eye relief of course.

I got tired of scratching my expensive daily wear eyeglasses on exposed metal on the top of eyepieces (even expensive ones like the 27mm Panoptic), so I bought a pair of distance-only eyeglasses off the internet for $20 that work great for astronomy.  They live in my astro tool box of miscellaneous bits and pieces.

I'm sure there are places over in the UK similar to the ones here in the US where you can pick up a perfectly good pair of prescription glasses for cheap.

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