RC8/RASA8 or EdgeHD8 + Hyperstar? - Forums

Topic starter

IOTD Staff

Jun 14, 2022

Alright fellas,

Here is the situation; as of now I have an RC8 and RASA8 as my two major telescopes. Lately I have been thinking of trading them out for just an EdgeHD 8 system. I won't consider any larger aperture so there's no point trying to sell me on that. I still need to set up and breakdown my gear pretty much every time I image. My goals are to do fast F/2 imaging, longer focal length objects such as galaxies and planetary nebula, in addition to planetary imaging. I know this is sacrilegious but I also do visual time to time.

As I see it now, with the RC8/RASA8 combo I have the "best in class" for longer focal length and F/2 imaging, since both are built to specialize in those things. This leaves me weak in planetary since the RC8 (in my experience) tends to struggle with it. The RC8 also struggles (again, in my experience) with visual. In addition to this, the RASA8 is a real pain to collimate not because I can't but because the design makes it god awful to do so for someone like me who has to break it down and set up every time. I don't want to spend the rest of my natural life waiting for the FCCT to come out for ZWO cameras and I am not dropping 800USD on one of those octo-pi things.

With the EdgeHD8 system, I instead get a jack-of-all trades but master-of-none thing going. My main concern for longer focal length imaging is the star bloating that the EdgeHD seems to get. Since I shoot mono now, I am not sure if that will be as much of an issue since each channel is getting focused individually. Having used a hyperstar on the C6 (sorry to spoil the surprise) I think its infinitely easier to collimate than the RASA8 just by virtue of being able to access the collimation screws at all times. You also are not rolling the dice on having the camera centered on the imaging circle every time you attach it. I'd imagine it would be the same for the hyperstar 8. My concern is that the EdgeHD8 with a hyperstar will have a noticeable drop of quality compared to the RASA8.

Thoughts and opinions?

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David Nozadze

Jun 14, 2022

Hi SemiPro,

I don't have any experience with either of your scopes, so I apologize for making a comment anyway. But, I thought, if I had to make the same choice, I would probably first replace only the RASA and keep RC8 for a while. The Edge indeed is a very versatile instrument. But, on the other hand, RC8 does have quite an impressive focal ratio at that focal length. I just bought my RC8 by the way and still waiting the clouds to clear up. Really looking forward to using it soon on some galaxies and planetary nebulas. My other scope, for wide field shots, is a newtonian astrograph.

Respectful

andrea tasselli

Frequent contributor

Jun 14, 2022 · Edited: Jun 14, 2022

Having used the older Hyperstar I feel that overall the results were quite good, but always an hassle to get in and out, beside having the cables dangling from the front. To be honest I'd take the old XLT with a reducer rather than the HD.

Lynn K

Jun 14, 2022

I used a C11 Hyperstar 3 in my earyly days of imaging. If you have used the C6/hyperstar, then you are well aware of the collimation issues when you break down each time. I havn't use the C11/Hyperstar in years. I now use a Tak FSQ106ED at F3.64 and I think the resolution is just as good as the C11 aperature.

I agrre with Andrea, if you are only going the use the Edge 8 for hyperstar, there is little advantage to the Edge. Starzonia's reducers F3.6 are far superior to the Celestrons F7, and are designed for the standard SCT not Edge. They will also accomodate a 2" focuser back focus. However, I have a Edge 8 that I use for visual, and it is not sacreligious. The field of view is sharp to the edge when viewed with Televue Panoptics/Delos. Even though I do mainly imaging, I have never used the Edge for imaging.

I too, have found that SCT scopes produce large stars. I picked up a older used carbon fiber C9.25 for $900, for galaxies and have been diapointed with the results. I use a older Starizona F7.5 reducer. I'm not sure if the newer F6.3 will produce better results. Dean, claims it will.

I think a refractor at or reduced to F5-6 will be a lot easier to deal with setting up each time. And may get as good or better resolution, despite the aperture. There is a lot to say about bringing the light to a fine focus. SCTs suffer from sperical aberation. It will not require optical and Hyperstar collimation each time. However, it will not offer you much for visual.

It seems you are looking for conformation of you resoning. It makes sence, if you want to do F2 Hyperstar and some visual. The Edge 8 will also do planetary and Planetary nebula at F10. Celestron does a better job of centering the EDGE seconadary on the optical axes than there regular SCT, since the spherical confiuration does not demand acurate centering, but the Edge flattener does.

Lynn K.

Matthew Proulx

Jun 15, 2022 · Edited: Jun 15, 2022

I've owned 3 RC8 an RC10, Edge925, 8/10/12" newt, 10" meade sct and a couple refractors. SCT do not produce larger stars IMO. I have star aligned and combined data from all of them and they are proportional to the FOV you are comparing to. By far the largest factor of star size is seeing, and thermals in the tube.

That said, you might not be any happier with a jack of all scopes if you have to deal with the swapping of the secondary and getting perfect alignment.
So much time is lost dealing with new scopes or changing equipment. I can speak to that.
RC8 vs Edge8 isn't really as different as you might think. One has spikes, one doesn't.
The thing I like about SCT is they stay clean, I live on a farm and theres 2 times of year where I get dust and pollen all over my scopes.

One of these images is from a 10" Newt one is from a 10" Meade SCT. The only difference is integration time.

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Tareq Abdulla

Jun 15, 2022

I can't call myself lucky or any of that, but i don't have enough budget to buy many different scope mainly the expensive or high end ones, so i keep thinking hundreds times about what to buy if i have a certain budget for one thing only, so that happened and i ended up buying the 10" RC or RC10 Truss, only because RC was my dream in the past, i was dreaming about 8" only, but this year maybe since last year i made the dream much much more higher and dreamed about CDK or even 12" RC from only 6"-8" RC years ago, now i have to be happy with it rather than thinking about having much more other models.

I already have refractors added last 2 years and also 8" Newt since 2018 and 6" Newt since 2020, also 7" Mak for anything but not DSO, so i think i am almost covered now and i will get back to astro imaging soon and see how those will do for me, later i can think about very fast optics or very large aperture scope, whatever can serve me better for what i want, with certain budget, i really want to have something like f/2 scope, but i can't keep paying a lot with my situations going on and this f/2 setup is also forcing me to buy other things like different filters different filter wheel and whatever else, i have time to decide and i hope by the time passing next years i can afford something very fast really.

SemiPro

Topic starter

IOTD Staff

Jun 16, 2022

David Nozadze:
Hi SemiPro,

I don't have any experience with either of your scopes, so I apologize for making a comment anyway. But, I thought, if I had to make the same choice, I would probably first replace only the RASA and keep RC8 for a while. The Edge indeed is a very versatile instrument. But, on the other hand, RC8 does have quite an impressive focal ratio at that focal length. I just bought my RC8 by the way and still waiting the clouds to clear up. Really looking forward to using it soon on some galaxies and planetary nebulas. My other scope, for wide field shots, is a newtonian astrograph.

Yeah giving up the RC8 would be tough. Really the only downside to it is in regards to planetary which is a big thing for me since I love planetary

andrea tasselli:
Having used the older Hyperstar I feel that overall the results were quite good, but always an hassle to get in and out, beside having the cables dangling from the front. To be honest I'd take the old XLT with a reducer rather than the HD.

I think it's a little better these days in terms of cable management with the rise of 3D printed routers.

Lynn K:
I used a C11 Hyperstar 3 in my earyly days of imaging. If you have used the C6/hyperstar, then you are well aware of the collimation issues when you break down each time. I havn't use the C11/Hyperstar in years. I now use a Tak FSQ106ED at F3.64 and I think the resolution is just as good as the C11 aperature.

I agrre with Andrea, if you are only going the use the Edge 8 for hyperstar, there is little advantage to the Edge. Starzonia's reducers F3.6 are far superior to the Celestrons F7, and are designed for the standard SCT not Edge. They will also accomodate a 2" focuser back focus. However, I have a Edge 8 that I use for visual, and it is not sacreligious. The field of view is sharp to the edge when viewed with Televue Panoptics/Delos. Even though I do mainly imaging, I have never used the Edge for imaging.

I too, have found that SCT scopes produce large stars. I picked up a older used carbon fiber C9.25 for $900, for galaxies and have been diapointed with the results. I use a older Starizona F7.5 reducer. I'm not sure if the newer F6.3 will produce better results. Dean, claims it will.

I think a refractor at or reduced to F5-6 will be a lot easier to deal with setting up each time. And may get as good or better resolution, despite the aperture. There is a lot to say about bringing the light to a fine focus. SCTs suffer from sperical aberation. It will not require optical and Hyperstar collimation each time. However, it will not offer you much for visual.

It seems you are looking for conformation of you resoning. It makes sence, if you want to do F2 Hyperstar and some visual. The Edge 8 will also do planetary and Planetary nebula at F10. Celestron does a better job of centering the EDGE seconadary on the optical axes than there regular SCT, since the spherical confiuration does not demand acurate centering, but the Edge flattener does.

Lynn K.

I'd use the Edge8 for small DSOs at F/7 with the reducer, "wide" field stuff at F/2 with the hyperstar, and planetary with a barlow x2 or x3. In terms of collimation, I find the hyperstar on the C6 holds collimation pretty good. I am actually astonished that you can plunk a beefy 2600MC on there and get it to work. The v4 hyperstars seem to have come a long way though I have never used the previous iterations.

Matthew Proulx:
I've owned 3 RC8 an RC10, Edge925, 8/10/12" newt, 10" meade sct and a couple refractors. SCT do not produce larger stars IMO. I have star aligned and combined data from all of them and they are proportional to the FOV you are comparing to. By far the largest factor of star size is seeing, and thermals in the tube.

That said, you might not be any happier with a jack of all scopes if you have to deal with the swapping of the secondary and getting perfect alignment.
So much time is lost dealing with new scopes or changing equipment. I can speak to that.
RC8 vs Edge8 isn't really as different as you might think. One has spikes, one doesn't.
The thing I like about SCT is they stay clean, I live on a farm and theres 2 times of year where I get dust and pollen all over my scopes.

One of these images is from a 10" Newt one is from a 10" Meade SCT. The only difference is integration time.

I am pretty sure one of those RC8's of yours is sitting in the room next to me! Just in case you are curious it's doing just fine and having checked the mirrors with a ronchi eyepiecce they are pretty much perfect.

If my C6 is anything to go off of, there is not a lot of down time between swapping the secondary mirror and the hyperstar. Maybe an adjustment here and there as the heavy lifting so to speak has already been done in previous collimation sessions.

The other option I an thinking of is just getting a dedicated 8" planetary scope like a standard SCT or perhaps a classical cassegrain. It would be more expensive than selling the RC8 + RASA8 and looking for a used EdgeHD 8 though.

I think my main concern is if the potential drop in quality is worth the trade-off. The appeal of collimating a hyperstar over the RASA8 (which is just horrible to collimate in my opinion) is one of the main draws. However after searching all over astrobin for Edge8/294MM and RC8/294MM combos I have to say the RC8 ones look cleaner with better stars.

I may end up just turfing the RASA8 but 8 inches of aperture at F/2 is really a solid time and a half.

In addition I might roll the dice on this which would be awesome on the RC8 and my FLT91: https://starizona.com/products/apex-ed-65x-reducer-flattener-for-apo-refractors-and-rc-acf-telecopes

Supportive

drblevy13

Jun 17, 2022

I bought an EdgeHD11/Hyperstar for the "jack-of-all trades" reason. I sold my Hyperstar last week so I can get a refractor with similar field of view and pixel scale as Hyperstar because I grew tired of getting everything perfectly lined up with one configuration only to have to break it down to set up the scope for another configuration. Having a setup ready to go at different focal lengths is more worthwhile to me. The tinkering around was fun at first, but after 2 years, I'm looking for the simplicity of 2 different scopes personally.

Although f/2 is much "faster," when I think of all the time I spent messing with tilt, collimation, rotation, and refocusing after manually changing filters, ultimately I probably will acquire just as much light with less effort with the new scope I just bought (Askar 107PHQ) at f/7! While definitely not as fast, the slower focal ratio is definitely more forgiving.

Comes down to personal taste though.

Helpful Insightful Respectful Engaging Supportive

Jun 17, 2022

Alright fellas,

Here is the situation; as of now I have an RC8 and RASA8 as my two major telescopes. Lately I have been thinking of trading them out for just an EdgeHD 8 system. I won't consider any larger aperture so there's no point trying to sell me on that. I still need to set up and breakdown my gear pretty much every time I image. My goals are to do fast F/2 imaging, longer focal length objects such as galaxies and planetary nebula, in addition to planetary imaging. I know this is sacrilegious but I also do visual time to time.

Then the Edge HD 8 could work for you if you're looking at F/2, and galaxies / planetary. I love my edge, and have had little to no issues with it. A heads up, you will probably end up buying the .7 reducer too if you are doing galaxies and such, as F/10 is... well... Slow and Narrow, believe me, I was stuck at F/10 until my birthday last year, and it really limited my potential.

If you don't care about those and have a mount that guides really well, then you'll be fine. Additionally, the Edge HD is MUCH easier to collimate than the RC (When you need to, every 2-3 years- mines stayed perfectly collimated since day 1 nearly 2 years ago.

) Also, the secondary obstruction is smaller on the edge, meaning you technically catch more light than the RC8 (all the better).

If you are intending to do galaxies, get the edge, if just planetary and H*, save some money and get the normal SCT, and its hyperstar, and maybe a Starizona 6.3R.

Also, Matthew Prolx has a massive astro-brain, so listen to him.

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drblevy13

Jun 17, 2022

I know a little off topic, but your mileage may vary with an EdgeHD 0.7x reducer. Many folks complain about bad field curvature with them. I gave mine up and have been elated at f/10. Field way flatter without.

Jun 17, 2022

I know a little off topic, but your mileage may vary with an EdgeHD 0.7x reducer. Many folks complain about bad field curvature with them. I gave mine up and have been elated at f/10. Field way flatter without.

(even more off-topic) So far I've got zero flat field issues with my Edge .7 reducer, so I cant say that my experience has been anything but great based on my experience. However, I have to agree about the field being better at F/10 (I was able to use it at Full frame with zero vignette). I got mine new in December, and they were the first new batch for ~7 months, so I think celestron *might* have put some better Q.Control into them for that small run. But I have seen some real horror stories about them, but many people have different experiences.

drblevy13

Jun 18, 2022

Very valid point. I have heard of folks that have had better luck than me. But I also saw lots of folks with similar experiences. But to address OP's original question, no doubt EdgeHD is a great system, but its flexibility is only proportional to your effort!

SemiPro

Topic starter

IOTD Staff

Jun 18, 2022 · Edited: Jun 18, 2022

I know a little off topic, but your mileage may vary with an EdgeHD 0.7x reducer. Many folks complain about bad field curvature with them. I gave mine up and have been elated at f/10. Field way flatter without.

I know a little off topic, but your mileage may vary with an EdgeHD 0.7x reducer. Many folks complain about bad field curvature with them. I gave mine up and have been elated at f/10. Field way flatter without.

(even more off-topic) So far I've got zero flat field issues with my Edge .7 reducer, so I cant say that my experience has been anything but great based on my experience. However, I have to agree about the field being better at F/10 (I was able to use it at Full frame with zero vignette). I got mine new in December, and they were the first new batch for ~7 months, so I think celestron *might* have put some better Q.Control into them for that small run. But I have seen some real horror stories about them, but many people have different experiences.

Totally on topic because this fits in the concern with optical quality. As far as I am aware the EdgeHD 9.25 has an excellent reputation all around but things start breaking down in the 8" variant if you get a bad sample. I can't imagine imaging at F/10 so I'd totally need the reducer.

Jun 18, 2022

Yeah, the 8 is reliable if you get the good ones, if you can find a new production version, they tend to have better optical performance, wider FOV with flat field, etc. The Edge .7 reducer is getting better and better as the years go on, most of the horror stories you see are from pre, or right after-2016-2018 (Celestron supposedly altered the Edge HD design to accommodate full-frame sensors around that time, which created new issues with the optical design).

And if you get a bad one, I wouldnt worry about it, since Celestron's CS is pretty good with defect replacements IMO.

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SemiPro

Topic starter

IOTD Staff

Jun 19, 2022

The more digging I do the more it is suggested that an RC cannot deliver a flat field. Now, I do use a 0.8x field flatterer/reducer which corrected my star shapes in the corners, however according to CCD inspector the field is still not flat so I am assuming I just fixed the astigmatism that is inherent in the RC system. I am not sure if that even makes sense.

I like cramming as many things as I can into the FoV, as well as mosaicing, which means I need a solid flat field all around. So maybe this is a point towards the EdgeHD? Or am I blowing hot smoke here?

I am not an optical engineer after all.

Engaging

Jun 20, 2022

Edge HD has a wonderful flat field in my experience, sometimes if I dont shoot inside the Denver light dome, I dont need flats at all other than to correct my dust.

SemiPro

Topic starter

IOTD Staff

Jun 26, 2022

Edge HD has a wonderful flat field in my experience, sometimes if I dont shoot inside the Denver light dome, I dont need flats at all other than to correct my dust.

Ah man that is tempting.

So for anyone who cares here is an update:

I have decided to keep the RASA8 for now. Using an angle grinder (yes, an angle grinder) I shaved down the starizona filter slider I have in order to get the proper back focus for my system. As is tradition in the welding trade, sketchy work with an angle grinder paid off in the end!

For the tilt issue I just decided to bite the bullet, ignore what everyone says about NOT TOUCHING THE COLLIMATION SCREWS, and just treat the RASA8 as a glorified hyperstar. I adjusted the tilt by, you guessed it, TOUCHING THE COLLIMATION SCREWS. Ahhhhhhhhhhhhh!

Gotta tell you, worked like a charm. I have never seen a flatter field on this RASA before.
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The jury is still out on the RC8. During a full moon I'll have to mess with it to see how flat I can get the field. The more I think about it, the more I don't want to give up its superb imaging qualities that it has over the EdgeHD, in my opinion anyways.

A lot will depend on how the new Night Owl reducer turns out since I think they are making it for the HD versions as well.

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SemiPro

Topic starter

IOTD Staff

Jul 4, 2022

Alright a final update:

I have given up on the EdgeHD 8 dream for a few reasons:

I am not a fan of the stars, especially the fringing on the blues that seem to plague some of the EdgeHD 8 / Reducer combos. Maybe the newer production runs are better but who knows. This relates to my next point.
This is particular to my RC8, but having used a Ronchi eyepiece on it has shown it to be free of any kind of mirror defects that it can detect. I am not sure I want to roll the mass production dice on a new scope when I know I have as close to perfection as I am going to get right now.
I have come to the conclusion that reducing an EdgeHD 8 to F/4 with a Night Owl does not make a lot of sense when you can just buy a F/4 Newtonian instead and keep the large imaging circle. 800mm of FL is also awkward for the 294mm in terms of pixel scale.
Comparing RC8 and EdgeHD 8 planetary shots, the slight gain in quality that the EdgeHD 8 gives its definitely not worth 2000 (or 1000 if I sold the RC8) dollars in my books. I have come to the conclusion that if I really want high quality planetary shots it won't come from an 8" telescope.

I am going to try the Apex-L on the RC8. It gets me down to F/5.2 and a crisp 0.90" /px scale. That, in addition to the 0.8x reducer/flattener I already have makes for a versatile long focal length platform. I can also slap the Apex-L on my FLT91 to get it down to F/3.8 which would be just fantastic.

I don't mean to knock the EdgeHD 8 because I think if I was to do it all over again I would of bit the bullet and gotten that instead of an RC8. That was the original plan anyways. If anything, I can see myself getting an EdgeHD 9.25 after university as I have seen nothing but the best from those scopes.

Thanks for the input fellas, it helped me sort this out and think about things for the far future!

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