Wide field eyepiece for fast scopes - any suggestions?

[RobertI]

OK, my ES68 24mm has arrived, courtesy of a fellow member. Initial observations:

• Slightly smaller than the Hyperion 21mm but similar weight
• Tighter eye relief (won't be a problem I think as I don't wear glasses)
• Smaller eye lens
• No undercuts!

The real test will be 'in the field' and I'll update this thread as I find out more. 

[Don Pensack]

34 minutes ago, RobertI said:

OK, my ES68 24mm has arrived, courtesy of a fellow member. Initial observations:

• Slightly smaller than the Hyperion 21mm but similar weight
• Tighter eye relief (won't be a problem I think as I don't wear glasses)
• Smaller eye lens
• No undercuts!

The real test will be 'in the field' and I'll update this thread as I find out more. 

The ES 24mm has always had a conical taper undercut on the barrel.  I've seen them since the 2009 beginning, and they've always had that.

It's a conically tapered undercut rather than a cylindrical one, but it is an undercut nonetheless.

[RobertI]

35 minutes ago, Don Pensack said:

The ES 24mm has always had a conical taper undercut on the barrel.  I've seen them since the 2009 beginning, and they've always had that.

It's a conically tapered undercut rather than a cylindrical one, but it is an undercut nonetheless.

That's true Don, should have been more specific. I'm hoping it doesn't suffer the looseness that I get with the Hyperions and my 2" diagonal.

[RobertI]

Some more comparisons (bear in mind we are comparing a 24mm with a 21mm):

• ES68 is 65 grams lighter (308 v 373g)
• ES68 is 10mm shorter (body) 
• ES68 has no rubber protection/grip - the Hyperion has rubber coating on the body and shoulder - actually great for grip and protection
• ES68 has green coating, Hyperion has purple
• ES68 has a shallower eyecup, appears to be in line with the shorter eye relief
• ES68 has a sharper field stop - not sure how important this is in real world viewing

 

Edited October 5, 2022 by RobertI

[RobertI]

Had a very interesting hour outside testing the new eyepiece in the C8 + reducer and the 102ED. My main task was to compare it to the Hyperion. I used the double cluster, M31 and Polaris - conditions were not great, with a bright moon.

I’ve never done such an in-depth eyepiece test (I usually just observe stuff!) but I found it a frustrating experience for two reasons:

1. The results from an eyepiece seemed to vary from one moment to the next - ie: I’d test the Hyperion, then five minutes later test it again and get a slightly different result - I can only put it down to slight focus differences and perhaps position of eyepiece in the diagonal, possibly even eye positioning. Who knows? 
2. The eyepieces were so close in performance it was actually very difficult to say which was better!

Each eyepiece produced slightly different aberrations/distortions in the the C8, but at similar levels across the FOV, starting with field curvature then becoming astigmatism as moving further out from the centre. The ES68 was certainly not sharp to the edges (far from it) and the Hyperion was actually not as bad as I recall. From what I could tell, the ES68 showed pincushion distortion and the Hyperion barrel distortion, with the ES68 being more noticeable, but neither were a problem for observing.

As far as eye relief goes the experience was similar in both, as the eye guards seem designed to take the eye relief into account  (without spectacles) and your eyebrow just touches the eye guard when viewing. In terms of object brightness and detail I couldn’t really notice any differences, perhaps things might look different under really dark skies.

I did notice more of a difference in the F7 refractor, I would say the ES68 was marginally better in edge distortions, but I had to look very hard. As I noted in a previous comment, the edge of field distortions in the F7 are much less than the F6.3 scope anyway, plus I really don’t think that the F6.3 reducer is that good and would possibly be a tough challenge for any eyepiece.

So in summary I would say the the ES68 is a very slightly better eyepiece in terms of edge of field distortions but only noticeable in the F7 scope. But I think the  Hyperion had an advantage in that its shorter focal length would show less field curvature anyway (I believe?) , so in a more equal test the ES68 might have shown a more obvious gain. 

The ES is a good eyepiece and a welcome addition to the arsenal, perhaps not as aberration free as I was expecting, but I now have that wider FOV that I was after, and a good additional eyepiece for when I have the ‘twin cannons’ out!

Edited October 6, 2022 by RobertI

[Ags]

I am honestly surprised by this. I suspect the edge issues you see in the ES68 24mm with the C6 must be from the scope/reducer combination?

[Louis D]

I would also compare on axis sharpness, contrast, flare control, haloing, ghosting, etc.  You're generally going to do most of your critical observing in the central 50%.

[Don Pensack]

3 hours ago, Ags said:

I am honestly surprised by this. I suspect the edge issues you see in the ES68 24mm with the C6 must be from the scope/reducer combination?

The f/6.3 focal reducer is also a field flattener, so improves the image quality over f/10, and the lower power sees less interference from seeing.

[Don Pensack]

Characteristics to look for when testing an eyepiece:

Date__________________Scope______________

Eyepiece_______________________________Day  Night

1.       spherical aberration_________________________________________________________

2.       coma_____________________________________________________________________

3.       astigmatism________________________________________________________________

4.       field curvature______________________________________________________________

5.       distortion--type and amount___________________________________________________

6.       chromatic aberration--axial and lateral___________________________________________

7.       apparent field_______________________________________________________________

8.       eye relief___________________________________________________________________

9.       light scatter control--field and star outside field (glare)______________________________________________________________________

10.   SAEP_______________________________________________________________________

11.   CAEP_______________________________________________________________________

12.   Tint________________________________________________________________________

13.   Vignetting___________________________________________________________________

14.   Transmission_________________________________________________________________

15.   thermal issues________________________________________________________________

16.   field stop focus_______________________________________________________________

17.   impression of contrast_________________________________________________________

18.   EOFB_______________________________________________________________________

19.   Sharpness on axis/50%/edge____________________________________________________

Other comments about eyepiece____________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________

 

 

 

 

 

 

 

[Ags]

24 minutes ago, Don Pensack said:

The f/6.3 focal reducer is also a field flattener, so improves the image quality over f/10, and the lower power sees less interference from seeing.

I know - my 6.3 reducer does improve the image quality in my C6. But the OP did question the quality of their 6.3 reducer...

[RobertI]

1 hour ago, Don Pensack said:

Characteristics to look for when testing an eyepiece:

Date__________________Scope______________

Eyepiece_______________________________Day  Night

1.       spherical aberration_________________________________________________________

2.       coma_____________________________________________________________________

3.       astigmatism________________________________________________________________

4.       field curvature______________________________________________________________

5.       distortion--type and amount___________________________________________________

6.       chromatic aberration--axial and lateral___________________________________________

7.       apparent field_______________________________________________________________

8.       eye relief___________________________________________________________________

9.       light scatter control--field and star outside field (glare)______________________________________________________________________

10.   SAEP_______________________________________________________________________

11.   CAEP_______________________________________________________________________

12.   Tint________________________________________________________________________

13.   Vignetting___________________________________________________________________

14.   Transmission_________________________________________________________________

15.   thermal issues________________________________________________________________

16.   field stop focus_______________________________________________________________

17.   impression of contrast_________________________________________________________

18.   EOFB_______________________________________________________________________

19.   Sharpness on axis/50%/edge____________________________________________________

Other comments about eyepiece____________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________

 

 

 

 

 

 

 

That’s a useful list Don, thanks, although I don’t know what some of those things are, but I will investigate. I did examine the on axis views and I couldn’t really say there was an clear difference but perhaps if I knew what I was looking for it might be more obvious to me. Field stop focus was much better in the ES but not something that would affect my enjoyment. I couldn’t really see any obvious differences in tint, but perhaps looking at moon and planets might show that some more, although I wouldn’t do planetary with these eyepieces anyway. The deeper eyecup of the Hyperion did do a better job of reducing extraneous light which gave the impression of better contrast initially but I think this was a bit of an illusion.  I didn’t see any EOFB in either. 

[RobertI]

4 hours ago, Ags said:

I am honestly surprised by this. I suspect the edge issues you see in the ES68 24mm with the C6 must be from the scope/reducer combination?

I think I will discover more about the differences between them over time, as I observe different kinds of objects under different conditions. I may well change my opinion. Also worth noting that the conditions were far from ideal, with a bright moon in the sky.  

[Louis D]

3 hours ago, RobertI said:

I did examine the on axis views and I couldn’t really say there was an clear difference but perhaps if I knew what I was looking for it might be more obvious to me.

Try using a very bright star dragged across the entire field of both looking for stray light control before it ever enters the field of view, at the edge, and as it crosses the field.  Repeat with Jupiter.  It may well be they behave identically.

Next try viewing a dim star cluster right at the edge of being perceived.  Search along the Milky Way to find some relatively unknown dim ones.  See if there is any difference in presentation between the two eyepieces.  With this, you're testing for sharpness, transmission and contrast.  Dragging it across the field can also reveal vignetting if dimmer members simply vanish from view near the edge.

[Louis D]

On 03/10/2022 at 09:22, badhex said:

Would love to see a couple of pictures of this setup Louis! 

Finally got to taking pictures of the TSFLAT2 attached to my 2" GSO dielectric diagonal this weekend.  Please ignore the dust in the second picture.  I think it's on the mirror, not the flattener optics.  It doesn't bother me or the images, so I'm not about to touch it.

The diagonal may say OPT, but it's still GSO made.

[badhex]

5 hours ago, Louis D said:

Finally got to taking pictures of the TSFLAT2 attached to my 2" GSO dielectric diagonal this weekend.  Please ignore the dust in the second picture.  I think it's on the mirror, not the flattener optics.  It doesn't bother me or the images, so I'm not about to touch it.

The diagonal may say OPT, but it's still GSO made.

Thanks @Louis D - nice solution. I have been toying with the idea of an FF for one (or both) of my fracs, but always seen a lot of mixed opinions about how useful it is for visual. How crucial is the placement of the FF in the optical path (i.e. distance from objective or EP)? 

[Louis D]

14 hours ago, badhex said:

Thanks @Louis D - nice solution. I have been toying with the idea of an FF for one (or both) of my fracs, but always seen a lot of mixed opinions about how useful it is for visual. How crucial is the placement of the FF in the optical path (i.e. distance from objective or EP)? 

Supposedly, separation is dependent on focal length, but I've found that the same extra 15mm of separation from the diagonal body works fine for both the 432mm FL AT72ED and 600mm FL 90mm TS APO.  I removed the extra 15mm for the latter, but couldn't detect any difference visually, so I left it in to keep things simpler.  Since the GSO diagonal has a 112mm optical path according to Bill Paolini, that makes the total added separation distance about 127mm as compared to no diagonal/FF.

At first, I tried just screwing the TSFLAT2 onto the M48 filter threads of the original diagonal nosepiece.  It was clearly too much separation as the field got rather wonky.  It does help flatten the field of my 14mm Pentax XL, though.  If I pull it out of the focuser a bit as well, it gets a nearly flat field and sharpens up nicely to the edge.

I have found that high power, planetary images are better when I remove it because it adds some spherical aberration on axis.  It's totally invisible at mid/low powers (think of exit pupils greater than 1.5mm).

It really cleans up wide field, low power views and ultrawide mid power views.  It's similar to using a coma corrector in a Newtonian.  Once you've seen the correction effect, it's hard to go back to not using one.

Here are the suggested separation distanced based on focal length:

• focal length < 450 mm: 128 mm
• focal length 450-490 mm: 123 mm
• focal length 500-550 mm: 118 mm
• focal length 560-590 mm: 116 mm
• focal length 600-690 mm: 113 mm
• focal length 700-800 mm: 111 mm
• focal length ab 800 mm: 108 mm

I didn't think it would work for the 600mm FL APO based on this table since the diagonal enforces a minimum separation of 112mm unless I screwed it straight onto the diagonal body, but it seemed no different as compared to using 127mm of separation.  Experimentation is the key.

[badhex]

1 hour ago, Louis D said:

Supposedly, separation is dependent on focal length, but I've found that the same extra 15mm of separation from the diagonal body works fine for both the 432mm FL AT72ED and 600mm FL 90mm TS APO.  I removed the extra 15mm for the latter, but couldn't detect any difference visually, so I left it in to keep things simpler.  Since the GSO diagonal has a 112mm optical path according to Bill Paolini, that makes the total added separation distance about 127mm as compared to no diagonal/FF.

At first, I tried just screwing the TSFLAT2 onto the M48 filter threads of the original diagonal nosepiece.  It was clearly too much separation as the field got rather wonky.  It does help flatten the field of my 14mm Pentax XL, though.  If I pull it out of the focuser a bit as well, it gets a nearly flat field and sharpens up nicely to the edge.

I have found that high power, planetary images are better when I remove it because it adds some spherical aberration on axis.  It's totally invisible at mid/low powers (think of exit pupils greater than 1.5mm).

It really cleans up wide field, low power views and ultrawide mid power views.  It's similar to using a coma corrector in a Newtonian.  Once you've seen the correction effect, it's hard to go back to not using one.

Here are the suggested separation distanced based on focal length:

• focal length < 450 mm: 128 mm
• focal length 450-490 mm: 123 mm
• focal length 500-550 mm: 118 mm
• focal length 560-590 mm: 116 mm
• focal length 600-690 mm: 113 mm
• focal length 700-800 mm: 111 mm
• focal length ab 800 mm: 108 mm

I didn't think it would work for the 600mm FL APO based on this table since the diagonal enforces a minimum separation of 112mm unless I screwed it straight onto the diagonal body, but it seemed no different as compared to using 127mm of separation.  Experimentation is the key.

Thanks! Super useful. When I am back in gainful employment and can afford it, I think I might pick one up. 

Sorry @RobertI for hijacking the thread, normal service can now resume! 

[RobertI]

55 minutes ago, badhex said:

Sorry @RobertI for hijacking the thread, normal service can now resume! 

No problem, useful for me too. 🙂