RobertI

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.....

1 hour ago, F15Rules said:

I got up very early this morning (4am!), having woken up with a start and realizing that I hadn't put our bin out for collection (they pick up early, often at 06.30 am)! 

So I popped on my dressing gown and went quietly outside to the back garden to fetch the bin..

WOW!! I was greeted by the most beautifully clear, dark morning, with Jupiter still brilliant in the west..but what really caught my attention was Orion, rising majestically in the south east, with Sirius about 10 -15 degrees above the horizon. Fabulous.

I was just rivetted..even fresh out of the house I could see a large section of the Milky Way running almost north-south, and hundreds and hundreds of faint stars everywhere.

I decided to count the stars I could see inside the Orion Quadrilateral..I managed 29 in total with direct and averted vision, including the Belt trio but not counting Betelgeuse, Bellatrix, Saiph and Rigel at the corners of the Quadrilateral..

I've never managed that many before, so delighted at that👍🙂

Dave

PS It's now wall to wall foggy here, after a really heavy dew!🤦😂

 

 

Superb. I wonder whether you were still reasonably dark adapted after a long sleep? Never done early morning observing, must give it a go….

6 minutes ago, PeterW said:

Was very steady last night, got my best ever view, made yet better with a blue filter I happened to have with me. 
 

Peter

I also have a blue filter (Wratten 80A). I ALMOST put it in but decided against it in the end - will give it a whirl next time out.

9 minutes ago, MalcolmM said:

Very interesting comparison and as a refractor man, I'm cheering

Would love to see your sketches. At risk of offending the imagers, there's something more personal about a sketch, it's a personal record of what you actually observed!

Malcolm 

Thanks Malcolm. Yes at certain moments of clarity the detail became overwhelming - my sketching powers (and speed) were not up to the job!

On 02/09/2022 at 20:42, goddasgirl2021 said:

  its a good Question when you think about it, and as those who love and study Astronomy, that is the big Question, that we should  be asking our selves, as we look 

up into our Cosmos, the Two Big Questions Being what is the definition of Life, and  what does it mean to be alive??????

It's great that you are studying astronomy, good luck with your journey. I have a "mini-mission" in life to increase people's awareness of the universe around us and 'show' them what's up there through a telescope. Might just give people a new perspective on life and trigger them to start asking some searching questions. 

Very nice! I agree about a good observing chair being a game changer. The Berlebach is a quality piece of kit. I bought a Nadira observing chair after years of standing, and have never looked back. I think the Berlebach looks more stable and more comfortable with its padded seat - something I might have to add to the Nadira. I was also worried that the spaced slots would not give enough adjustment, but turned out to be just fine in the field.

Very enjoyable session on Jupiter last night with pretty good seeing. I used two scopes and got an interesting and surprising comparison between the two. Might even post a sketch later. Full report here.

Lovely dark transparent evening, had an hour or two on my hands, so planetary or deep sky? Well the seeing looked good so I thought I’d try Jupiter with the C8 and binoviewers and was not disappointed. The seeing got better and better and at 180x I was viewing some beautiful features, brown belts, grey streamers, white ovals and the beautiful Great Red Spot (now salmon pink!). I spent a good hour sketching and I may share later if I feel brave enough.

I thought I’d switch to the 102ED with BVs just to compare and, oh my, was I surprised. At around 170x the view was so much more pleasing, and the white/light areas and white ovals much easier to see. The disc was sharper, the features richer and more contrasty, the sky was darker and the moons had become tiny little discs. The only real downside was that floaters were getting in the way every now and then which is a pain. I was expecting under these decent conditions that the C8 would pull away from the 102ED but I was surprised.

I finished with a little deep sky - a view of the double double cluster. For fun I thought I would compare the view through the 102ED and  binoviewers at x57 with the C8 and single Hyperion eyepiece at about x60 - again I was expecting the greater light gathering of the C8 to provide much the better views but I actually  preferred the view through the 102ED with BVs - the stereo viewing, dark background, and pinpoint stars made for a really immersive experience. Need to work out how I can get more out of the C8 for lowish power viewing of open clusters and star fields. 
 

Edit: Sketch added, while trying to capture the detail I got the positioning a bit wrong, but hopefully of interest.

Great report, nice varied session by the look of it. 

Nice observing Nick and nice record keeping both of you. 🙂 I have really struggled to find a format that I like for record keeping over the years. I currently maintain a spreadsheet that I have been adding to over the last three years. I don’t like having an electronic solution, but I have found it pretty useful being able to search and filter to see previous observations of an object, sometimes with different scopes, and also being able to link to my SGL reports. If one thing, it has proved how fickle my memory is when recalling previous observations! 

9 hours ago, F15Rules said:

My biggest inspiration these days comes from looking through my scopes, whether at tiny point sources of light on clusters, globulars or the Milky Way, a sparkling half moon, the planets and brighter nebulae

Me too Dave. And without wishing to divert the thread, I think one area where astrophotography can never capture the visual experience is with doubles and clusters. Those perfect little pinpricks of light just can’t be recreated on paper or screen (yet!). I do like the challenge of tracking down faint fuzzies, but I’m not that turned on by the myriad of faint galaxies in the spring - that’s when I bring  out the EAA kit! 

1 hour ago, IB20 said:

This perfectly captures what I observed, great sketch. 

Thanks! And thanks for the heads up about the transit - I wouldn’t have known if I hadn’t spotted your post. 🙂

I did a rough  sketch at the eyepiece and tried a better rendition this morning. Not an expert at sketching but hope it conveys the overall view. 
 

Looks wonderful - a serious telescope. 👍

52 minutes ago, IB20 said:

When the shadow neared the planetary limb, Europa suddenly appeared, imposed just over it creating an amazing 3D effect between moon, shadow and Jupiter… just wow. 

Agreed, it was quite a moment to behold, the black shadow right next to the bright moon against the swirling clouds of the planet, and with the GRS nearby……just awesome.

I was lucky enough to have some great seeing at times, and the binoviewers in the C8 at around 170x revealed some wonderful detail in the cloud belts and around the GRS. One of those times when the C8 lived up to its potential for planetary observing. I wish my sketching powers were up to the job - next time I’ll have a go.

Great report and interesting comparison of eyepieces and filters. I have also found that binoviewers transform the planetary viewing experience.  Regarding Mars, as others have said, it can be spectacular when it’s at opposition, with lots to see, including the occasional dust storm, so give it a go later in the year! I had some fantastic views (see here and here ) with my 102ED refractor in 2020 so I would hope your 127 Mak can give similar views. Interestingly, reading my old report, I had noted that a yellow #12 filter helped a bit with Mars, which I’d forgotten. 

Fantastic! Sounds like you are on the start of a love affair with this wonderful hobby. You've got a great scope there - plenty of fun to be had and it doesn't have to be expensive - although it probably will be.  

Keep at it with Jupiter - it's just the start. If you can observe when the seeing is good (little atmospheric turbulence) and it is high in the sky, you can crank the magnification up to 150x - 200x and start to see amazing detail, fleetingly at first, takes practice, but it will come - great red spot, festoons, shadow transits - you've got a lot to look forward to.  

Edit: I should just should add that on nights of bad seeing, high magnifications won't help and you just won't see much detail, so also be prepared for some disappointments!  

I think a visual only magazine would be great but would probably be a bit too niche to make any money! I do get Astronomy Now, mainly to offer something different it sit down and read, although they do offer some interesting visual targets each month. You can’t beat SGL as a rich source of equipment reviews and observing reports for visual astronomers. I can also highly recommend the Actual Astronomy Podcast - Chris and Shane release a new programme each week and it’s purely about visual observing and is very entertaining - a bit like going down the pub with your favourite Astronomy friends! 🙂

Here is the original thread, hope it helps….