RobertI

You could hire a 10” dob for a couple of weeks to see how you get on. I’ve been thinking of doing this myself with a 12”, here’s a possible provider who is not far away  ……

https://www.darkskytelescopehire.co.uk/telescopes-for-hire/250mm-skywatcher-dobsonian-reflector-telescope
 

Personally, I think that even if you find the increase in aperture doesn’t show you enough of a difference, the move to a closed tube dobsonian with a better focuser will really improve your viewing pleasure and allow you to achieve more with those lovely Nagler eyepieces. 

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.  

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. 

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!

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

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.

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. 

2 minutes ago, paulastro said:

If you nake it to Kelling in the Spring, pop by and say hello, I'll be on T137 for the week 🙂.

Excellent, thanks Paul, will do (I take two sugars 🙂).

25 minutes ago, markse68 said:

Oh and the Owl looks more like a Bat to me

25 minutes ago, paulastro said:

for me it's ET every time, and I'm sure he winks at me

It’s definitely ET for me too, especially when he’s the right way round. I laughed out loud the first time I saw it. It always surprises me how big it is, especially when compared to some of the smaller clusters in Cassiopeia. I am really hoping to get to Kelling in the Spring, even if I just go for one evening. I went a long time ago and the skies were amazing. When I looked towards Andromeda through binoculars I thought a small cloud was passing - it was M33!! 

2 hours ago, Nik271 said:

Nice! Actually I find your diagram more uselful than a list, great challenge for big binoculars too! (In my view many open clusters look best in binoculars)

1 hour ago, Stu said:

Quite handy to show them highlighted on SkySafari though. Would be better on an iPad not a phone.

Yes I actually really enjoyed sitting at my desk with a coffee and my copy of Interstellarum and working out what to view. The process of identifying them and drawing a diagram on paper really helped me to familiarise with the clusters in that area. Interstellarum is fun to use and always provides some additional insight. I have to say though, when I am out in the field, I always seem to end up using Sky Safari (iPad version of course 😉). 

Ok, so you’ve really made me think here (I should never have claimed it’s the “twenty brightest”, just “twenty of the brightest”). I’ve created a list from Sky Safari of the actual twenty brightest which can be imported into Sky Safari. Naturally it bears little resemblance to my list. 😆

Twenty Brightest OCs In Cassiopeia .skylist

…but you’re making me think I should put together an accurate list of the top twenty in Cassiopeia for others to use ….. I’ll see what I can do. 🙂

48 minutes ago, PeterW said:

 Pyle you post a list of the 20, maybe in nominal brightness order, be good to add to sky safari and go after sometime, seeing that Cassiopeia is so well placed at the moment.

Peter 

To be honest Peter I can’t definitively say it’s the brightest twenty, but I think it comprises 90% of them. Here’s a little pic I drew to help keep me ‘focussed’ on the project. Also attached is a table from Norton’s sky atlas which may not include everything on my list. May not be exactly what you’re after……

Did a bit more observing with the Hyperion 21 last night, with the C8 and F6.3 reducer/corrector. The first thing to note is that the previous time out I was using the double cluster to do the testing - I realise now this was a poor choice as the two clusters are spread out over the FOV and exaggerates any problems and not typical of most clusters I look at where the object sits in the middle of the FOV. So when I observed some other clusters tonight the effects were not so obvious, and the experience was much better.

So doing some closer examination this time, I found that the stars started losing definition from about 50% out from centre, but could be focussed with a small adjustment (implying field curvature?). When getting to the extreme outer edge, lots of seagulls appeared which changed shape when focussing (astigmatism?), but only at extreme edge and not noticeable in normal use. I think I could detect barrel distortion when panning, but not a problem for normal viewing of objects. I did try swapping from my 2" SCT diagonal to a 1.25" prism diagonal and if anything the issues were slightly worse, certainly no better. 

I changed the eyepiece to the 102ED F7, and the results were better, with the stars losing definition from further out from the centre (about 60-70%). Forgot to check the extreme edges. Will try with an F5 scope and see what happens.

So it was interesting to do these tests in more depth, and armed with a bit more knowledge from this thread, to really understand what's going on.

I now have a used ES68 24mm on the way hopefully, and will do a comparison with the Hyperion.    
 

A lovely session last night starting my quest to observe the twenty brightest clusters in Cassiopeia. It’s nice to have a little project. 🙂 More details here . 

12 minutes ago, josefk said:

Nice one Rob. i've had maybe 4hrs 30 mins in Cassiopeia over the last week in three sessions and finding it very instructive to concentrate and keep returning to a small defined area. In one month i will have forgotten everything so for my self i would say "i have temporarily learned a lot" 🙂.

M103 vs NGC 663 is a strange one isn't it? It's even in the same FOV at binocular and low mag viewing and like you say considerably more prominent.

Enjoy the other sixteen stars.

Thanks, yes I agree, it’s very instructive to concentrate on a small area - Cassiopeia is a great constellation for doing this. When I zoomed right out out to 24mm I could JUST see all three clusters in the FOV. Very nice. 

I decided on a whim last week to try and observe the twenty brightest clusters in Cassiopeia, so I spent one evening doing some desk research using my various atlases and compiled a little list - it was fun and I learned a lot, something to remember for a rainy night . Last night was clear so I started on my little challenge. I concentrated on a small group of clusters in the bottom of the 'W', namely NGCs 654, 659, 663 and nearby M103. Observing was primary through the 102ED with a Hyperion Zoom.

NGC663 was the most spectacular, even more so than M103. It was prominent in the 10x60 finder and easy to find. Why it's not not Messiers list is a mystery! It was  large with around 20 bright members and a similar number of fainter ones.

Moving on to nearby NGC654, much smaller with two bright members and number of smaller ones. 

Then finally NGC659, fainter than the others, looking like a small haze with hints of stars visible with averted vision. Through the C8 it was possible to resolve many of the stars and I suspect if I zoomed in even more would have been visible.

Nearby M103 was a disappointment considering it's a Messier object, fairly sparse with some bright members. 

 Four down, sixteen to go. I shall continue my quest next time out 

Great report Jeremy.  Nice location to observe from, a great haul of targets. 👍 I need to try out some IS bins sometime!

15 minutes ago, bosun21 said:

That’s a lot (50%) of the field to be seeing distorted stars with a Hyperion. I have tried them in both my f6 dobsonian and my f12 Maksutov. Whilst the stars started losing their form in the outer 15-20% of the f6 this was hardly noticeable in the f12. Could it be the collimation of your C8?, or maybe try without the reducer. It’s just that half the field being distorted sounds as though there’s something else at play.

   Ian 

Yes I have wondered whether something is going on, although my 50% figure is incredibly unscientific and probably exaggerated. Pretty sure collimation is good, out of focus stars are concentric and I was getting some really good detail in Jupiter the other day. The other thing was I was using a 2” SCT diagonal, which has a longer light path and might possibly make the issue worse with the corrector. I was thinking about trying with the 1.25” visual back and prism diagonal just to see if a noticeable difference. But I did read an old observing report where I noted it was not so good with the F6 72ED I used to have, so perhaps just not so good with faster scopes. I’ll also have a go with the F7 frac and F5 newt just to see. 

1 hour ago, badhex said:

I went through a similar process a while ago looking for a maximum TFOV 1.25" EP - I settled on the the UFF in the end and I'm very happy with it, it performs equally well in both my usual fracs at F7 and F5.9. True to the name, the field is extremely flat all the way to the edge, and it seems that most real world tests show that the TFOV turns out to be very close to both the Panoptic and ES despite the AFOV being a few degrees less. The Pan is a bit lighter than the ES and UFF. 

The UFF also has quite long eye relief, so good if you wear glasses - I do not, but in another thread I discovered that I personally need *less* eye relief than some people, and the APM has an M43 thread under the supplied eyecup, so I replaced it with a Baader Morpheus eyecup plus extension. Helpful that you can tweak it if needed. 

The Panoptic has a lot of rectilinear distortion and I'm fairly sure I read the ES has some too - but an owner would have to confirm that. At any rate, the UFF has very little if any. 

One last thing that might be of interest: I have found that I much prefer EPs with large eye lenses from a comfort perspective. The UFF is about 30mm, approx the same as the Morpheus range (which I also really like). 

Thanks, that's really useful, but also slightly annoying as I was erring toward the ES68! 😄 I also like large eye lenses - that is one thing I DO like about the Hyperion. I see that the Altair version of the UFF is quite a bit cheaper than the APM - assuming they are the same eyepiece (they seem to be - I think Celestron do a version too) can you think of a reason for this?

2 hours ago, cajen2 said:

Can you use 2" EPs? If so, both the 14 and 20mm StellaLyra LER/UWA are excellent. They show no edge of field aberrations in an F/6 scope - sharp to the edge. There are also 1.25" ones in the same range but I haven't tried those.

My favourite wide-field EPs are Baader Morpheus. Don't be put off by your Hyperion experience: these are a very different kettle of fish. Again, clear and sharp to the edge in my scope. YMMV.

I can use 2" eyepieces in the C8 but I understood that you get vignetting due to the limited size of the internal baffle of SCTs, but I wonder if this would happen with a 2" eyepiece of only 20mm? An interesting proposition as this would give a similar field of view to the 24mm 68 degree eyepieces, but at a slightly higher magnification.

2 hours ago, Ricochet said:

No, these are different things.

Field curvature/flatness is where the focus position is across the entire field. In a flat field scope and eyepiece the focus position in the centre of the field is the same in the centre of the FoV as at the edge and so stars that appear as pinpoints at the centre of the FoV also appear as pinpoints at the edge. In a scope/eyepiece with field curvature the focus position at the centre of the FoV is different to at the edge of the field. Stars appearing as a pinpoint at the centre become a small disk as they drift to the edge, but when they are at the edge you can wind the focuser in or out to make them a pinpoint again. If there is a small amount of field curvature it can often be reasonably overcome by focusing on a star 1/3 of the way from centre so that the image appears reasonably flat across the whole FoV. The UFF designers have prioritised keeping the image plane flat, but this does not tell you anything about any other distortion or aberrations that may exist. From experience I know that the 24mm ES68 has a small amount of field curvature (at f6) if you look for it, but this is quite minor and enough to be a reason to ignore it.

The opposite aberration to field curvature is astigmatism. This is where instead of a star being stretched into a circle by field curvature it is stretched in a manner that is not radially symmetrical. Stars can appear as lines, curves, crosses or seagulls. I do not recall this being noticeable in the ES68. By prioritising a flat field it is possible that the UFF shows some astigmatism at the edge. However, I recall that the UFF is quite a large eyepiece, I think even bigger than the ES68. This could well be the reason for that size: in order to control astigmatism whilst keeping the field flat the designer had to add more elements to the eyepiece. People who have actually used the eyepiece will have to advise on this although from the reputation of the eyepiece it will either be very minor or not noticeable.

When it comes to field distortions there are two distortions. Rectilinear distortion, where straight lines become curves at the edge of the field, and angular magnification distortion, where the magnification in the centre of the field is not the same as the magnification at the edge. One of these increases in the form y = x and the other with y = tan x and so once you have an eyepiece with an apparent field over ~40° you have to have one or the other, or a mix of both. It is impossible to correct for both. If you reduce one you will increase the other. Typically minimising rectilinear distortion is preferred for terrestrial targets and minimising angular magnification distortion is preferred for astronomy. The ES68 has a small amount of RD (and so must also have AMD) and so I have kept a Meade SWA (the predecessor to the ES68) for my spotting scope instead of using a 24 Pan which has lots of RD. I have not used a UFF to know what distortion balance their designer chose but in practice I am not really bothered by either for astronomy as I tend to focus on one target at a time instead of quickly sweeping across large star fields.

No, these are the best two options where the choice is "not a Panoptic".

Thanks for taking the time to explain, that's a nice simple summary. I think I probably confused myself by reading a review comparing the two eyepieces, and then trying to interpret the conclusions of that review based on insufficient knowledge (and the consumption of two beers). Sounds like you have found the ES68 to be a decent eyepiece.

Having recently posted a topic describing how I have never really been that fussed about eyepieces, I recently tried some rare wide(ish) field viewing with my C8, and when I examined the field of view, I was pretty unimpressed. I was using my F6.3 reducer/corrector and my Hyperion 21mm. Hyperions aren’t famed for their edge correction (so I believe) and the star shapes started to become very distorted about 50% of the way to edge. Not particularly pleasant for viewing large clusters and Milky Way. I swapped with my William Optics 20mm SWA 66 degree eyepieces from my binoviewers, and they were even worse! So I’m wondering, how can I get a nice flat field low power view with my C8 @F6.3?

So far I have narrowed the eyepiece choices down to the UFF 24mm 65 degrees (APM and Altair do these) at around £125 and the Explore Scientific 24mm 68 degree at around £175. My understanding is the UFF gives a flat field, which means no fishbowl effect or ‘field distortion’, but does produce less than pinpoint stars towards the edge. I believe the ES gives the reverse, some fishbowling, but pinpoint stars right to the edge.

So assuming my understanding about these eyepieces is correct, what do people think is a better experience - no ‘fishbowling’ or pinpoint stars to the edge? I’m inclined to say the latter, but interested in people’s experiences.

Also, are there other 24mm 68 degree eyepiece, or thereabouts, which would work well in fast scopes? I can’t afford a Panoptic btw! 🙂

 

Nice images Chris - the achro has done pretty well there. Conditions were pretty good on Thursday - I was out doing some sketching of Jupiter so interesting to compare with your image. What’s the GRB by the way? Great Red Blob? 😉

4 hours ago, IB20 said:

Maybe I need to try a contrast booster on the 8” light bucket.

Yes I have thought about something to reduce the glare with the 8" - perhaps I'll try a yellow filter or moon filter.....