Meade LX200ACF 10" or Celestron EdgeHD 9.25 or 11"
Hi everyone,
I would be interesting in hearing people's opinions on the differences in optical quality of the larger SCT scopes: Meade LX200ACF 10" or Celestron EdgeHD 9.25 or 11".
I am considering purchasing one of these to mount on my Celestron CGEM. I will mainly use it for visual, but would also like to do some webcam astrophotography of the planets and maybe bright globulars/nebulae.
Which scope would be the better? Both are similar in weight but use different optical designs to achieve reduced coma and field flatness. Which one achieves the best result? In the USA, they are similarly priced so pricing is not my main concern.
Mate, if you want to drive to Mudgee one weekend or meet in the mountains, you can borrow my Meade 10" ACF and see what you think, or just come up and have a look through it here.
I see no difference between the flatness of field between the Meade and the Celestron EDGEHD, there is definitely a difference between the and the standard SCTs though.
The celestrons have the advantage of Hyperstar if you are thinking of photography, and its okay Brendan, I'm not a fan of Newts or Dobs
You may want to check the weight of each OTA, the CGEM is only equivalent to the EQ6Pro in how much it can carry for photography, but any of them will be great on planetary and globular clusters.
The main issue with all of them is cooling, but I have found that easy enough to work around.
Really the differences between them are negligible optically they all perform as well as each other.
Hi James , for planets it's got to be the 9.25 , and deep sky apateaure rules , so the 11 inch .
I have friends with both and they are both really good .
Oh yea the Meade is very good optically but it is as heavy as the Celestron 11 inch and much heavier than the 9.25 inch .
Something to think about .
Brian.
My 10" is the same weight as the C11, and side by side with the 9.25 it has always delivered better images of Jupiter, without exception. The 10" gives you 20% more light grasp than the 9.25 which, not drastic, but noticaeble. The Meade also has mirror lock and for non planetary work the flat field of the ACF is a big advantage.
I think the 9.25 is a great scope, but I think its reputation exceeds its reality a bit. Yes it is a *little* flatter than the C8 or C11, but nowhere near as flat as the Meade ACF or Celestron EDGE HD scopes. The only advantage I see it having is weight, I think it is about 2.5kg lighter or so.
Not sure which is easier to cool down to ambient temperature.
I also have a celestron C8 and the M10 gives way better images on planetary. I haven't had a chance to side-by-side with the C11, I would be interested in seeing how it compares, as it has the hyperstar option for DSO work, and is a large enough aperture to put a decent camera on it.
I am leaning towards the C11 EdgeHD as it is the biggest that I can mount on the CGEM and with Hyperstar compatibility, I can do much shorter exposures.
and its okay Brendan, I'm not a fan of Newts or Dobs
Hi Peter,
As a visual instrument there is not one single performance criteria where a SCT telescope can outperform a newtonian and in many performance criteria as a visual instrument they are clearly inferior.
There are many reasons why people want to own and use a SCT for visual astronomy and they are vaild for each individual and their circumstances, but optical capability isn't one of them.
If you want I am happy to spell each and every one of them out for you. Its pretty simple optics and physics. The optical and physical theory is backed up by what I have experienced at the eyepiece comparing the two scopes countless times over several decades.
As an imaging telescope it's a whole different ballgame.
Thanks for your input. My understanding is that the central obstruction in the SCT is their weakness. The other weakness must be the combination of using the corrector lens and then two other mirrors. The image has to degrade more than a refractor or newt dob.
My preference would actually be for a nice 6" APO Triplet refractor, but my budget falls short by around $7000! The main requirement is that I want the telescope to easily fit in the boot so that I can take it camping with my kids and friends.
The SCT fits my needs as I can get what I think is big aperature in a small package. I currently own a 6" Achromat Refractor, it is great but I want more aperture and less chromatic aberration on planets. I looked through a C9.25 SCT at IISAC on the weekend at Jupiter. It was truly a beautiful site!
As a visual instrument there is not one single performance criteria where a SCT telescope can outperform a newtonian and in many performance criteria as a visual instrument they are clearly inferior.
There are many reasons why people want to own and use a SCT for visual astronomy and they are vaild for each individual and their circumstances, but optical capability isn't one of them.
If you want I am happy to spell each and every one of them out for you. Its pretty simple optics and physics. The optical and physical theory is backed up by what I have experienced at the eyepiece comparing the two scopes countless times over several decades.
As an imaging telescope it's a whole different ballgame.
Cheers,
John B
I get consistently better results on planetary on my C8 than other people with my experience level get on their 8" newts. The best amateur planetary photography I see online is done on C14's and SCTs. I also am not a fan of diffraction spikes. I find the SCTs much easier to handle and setup and use, and I much prefer the eyepiece position for most viewing.
I can add a hyper star and image at F2 for not a huge investment, and have a really compact scope that can do planetary and ultra fast DSOs and not be out all night getting enough subs.
An 8" newt is nearly twice as long as my C8, and nearly 3kg heavier than my C8. A 10" newt is what, about 1.2m long and about 16kg vs 60cm and 13kg for a C11. I find an SCT far more usable to mount and move around, especially with cameras attached. So for a Newt and an SCT of the same physical size, the SCT will kill the newt optically, as I can have an 11" SCT for the same length as a 6" newtonian.
There are a ton of reasons why a newt is 'better' than an SCT, there are plenty of reasons why a refractor is better than a newtonian, and an RC better than... and so on. There are reasons an Android phone is better than an iPhone and vice versa.
The best scope is the one you use as they say, I personally found I didn't use the 10" newtonian I had in the late 80s, I sold it and bought a C8 on a simple fork and used the hell out of it, as I could just grab it by the forks and chuck it in the passenger seat. I used to take it camping, it went everywhere with me, and it took lots of photos on hypered film through my poor old olympus SLR.
For critical viewing there is always a better telescope than the one you own, anyone can argue up and down all day why the one they prefer is the best, and just about everyone can prove they are right
That's why I said "I'm not a fan", and put a 'wink' after it, rather than saying "SCT is better".
It is simply stating that I don't personally like them, not that SCTs are necessarily a better scientific instrument, just that I get more enjoyment (and therefore better results) using one. They are a popular scope and suit a lot of people. So are refractors, so are newtonians and dobs, RCs and Maks, we are spoiled for choice these days, which is a great thing.
I've become a huge fan of refractors in the last month or so, but again, a 4" one is my personal sweetspot until the day I can afford to buy my own house and setup a permanent observatory.
If you want to borrow either the C8 or the M10, let me know. The C8 is a trooper, and has proved relatively indestructible so you wouldn't have to worry about it getting wrecked, and it is on its clunky little forks so goes straight in the boot for those camping trips.
Quote:
Originally Posted by dulwich.hill
Hi John,
Thanks for your input. My understanding is that the central obstruction in the SCT is their weakness. The other weakness must be the combination of using the corrector lens and then two other mirrors. The image has to degrade more than a refractor or newt dob.
My preference would actually be for a nice 6" APO Triplet refractor, but my budget falls short by around $7000! The main requirement is that I want the telescope to easily fit in the boot so that I can take it camping with my kids and friends.
The SCT fits my needs as I can get what I think is big aperature in a small package. I currently own a 6" Achromat Refractor, it is great but I want more aperture and less chromatic aberration on planets. I looked through a C9.25 SCT at IISAC on the weekend at Jupiter. It was truly a beautiful site!
I get consistently better results on planetary on my C8 than other people with my experience level get on their 8" newts..
Hi Peter,
That is scary. Leaving the observer out of it, I can only question the quality of those 8" newtonians. I have looked through a lot of different SCT's over the years (50 plus) and never yet seen one that can equal a good newtonian, of equivalent aperture, as a visual scope for planetary use. My good friend Rod Berry had a 10" LX200 and was so dissappointed with the views in that scope compared to my 10" newtonian that he sold it and bought a newtonian. Similarly, I have used several different 8",9.25",10",11",12" and 14" SCT's and none of them equal my 10" newtonian. What my 14" SDM with Zambuto mirror does to them is laughable. The 16" LX200 at Sydney Observatory, which I have also used, I could only rate as "average at best".
Quote:
Originally Posted by Poita
The best amateur planetary photography I see online is done on C14's and SCTs..
I did say, "Imaging is an entirely different ballgame"
That having been said Damien Peach could take outstanding images with a Box Brownie camera stuck on the end of Galileo's Telescope. I have no doubt that if Damien Peach were to image with a high grade newtonian his images would be just as good, if not better, than what he does now with a SCT.
Quote:
Originally Posted by Poita
I also am not a fan of diffraction spikes..
That's fine and I appreciate many people dislike diffraction spikes. It's a matter of personal preference, but for the record a newtonian with a curved vane spider solves that problem easily.
Quote:
Originally Posted by Poita
I find the SCTs much easier to handle and setup and use, and I much prefer the eyepiece position for most viewing.
I can add a hyper star and image at F2 for not a huge investment, and have a really compact scope that can do planetary and ultra fast DSOs and not be out all night getting enough subs.
An 8" newt is nearly twice as long as my C8, and nearly 3kg heavier than my C8. A 10" newt is what, about 1.2m long and about 16kg vs 60cm and 13kg for a C11. I find an SCT far more usable to mount and move around, especially with cameras attached. So for a Newt and an SCT of the same physical size, the SCT will kill the newt optically, as I can have an 11" SCT for the same length as a 6" newtonian.
Those are all ergonomic reasons and imaging reasons; and all very valid. Don't however lose sight of the fact that a "truss" style newtonian is at least as portable, if not more portable, than an equivalent aperture SCT. It isn't however any good for imaging.
Quote:
Originally Posted by Poita
there are plenty of reasons why a refractor is better than a newtonian
There aren't because once you get to anything like "decent" aperture (10" plus) a refractor becomes unmovable and cost prohibitive and a larger aperture newtonian will always beat out a smaller aperture refactor. A smaller refractor may give an aesthetically cleaner/nicer view, but you will not get the same level of detail out of the smaller refractor.
Quote:
Originally Posted by Poita
For critical viewing there is always a better telescope than the one you own, anyone can argue up and down all day why the one they prefer is the best, and just about everyone can prove they are right
I am yet to find one that gives "consistently" better "lunar/planetary" views than my 14" SDM with Zambuto mirror. That includes scopes up to 36" aperture and the exquisite 15" D & G Refractor at 3RF's Comanche Springs facility in Texas. Also consider that the 15" refractor is housed in a 35 foot dome (see attached photos). My 14" SDM easily fits in the boot of a Toyota Corolla and takes 15 mins to pack up.
To give you some idea of the size of the 15" refractor consider that the "little finderscope" sitting on top of it is a 6"/F12 D & G refractor. The white scope sitting on the rocker box of the 36" Obsession Scope is a 6" Celestron Comet Catcher
Quote:
Originally Posted by Poita
I've become a huge fan of refractors in the last month or so, but again, a 4" one is my personal sweetspot until the day I can afford to buy my own house and setup a permanent observatory.
A 4" refractor is an excellent imaging scope. However, by todays standards given the proliferation of large aperture high quality newtonians at reasonable prices, I rate a 4" refractor as not much more than a finderscope for serious visual astronomy.
I have no doubt that given James's stated needs, where he wants something portable that he can use for imaging, a SCT is clearly the best choice for him. However, he shouldn't be under any illusion or belief that his chosen SCT will equal the optical performance of an equivalent aperture high quality newtonian. It will be a compromise based on his ergonomic and imaging needs.
Cheers,
John B
Last edited by ausastronomer; 04-11-2011 at 03:35 PM.
Thanks for your input. My understanding is that the central obstruction in the SCT is their weakness. The other weakness must be the combination of using the corrector lens and then two other mirrors. The image has to degrade more than a refractor or newt dob.
My preference would actually be for a nice 6" APO Triplet refractor, but my budget falls short by around $7000! The main requirement is that I want the telescope to easily fit in the boot so that I can take it camping with my kids and friends.
The SCT fits my needs as I can get what I think is big aperature in a small package. I currently own a 6" Achromat Refractor, it is great but I want more aperture and less chromatic aberration on planets. I looked through a C9.25 SCT at IISAC on the weekend at Jupiter. It was truly a beautiful site!
James
Hi James,
If you have any desire to image and you need portability then the SCT or ACF design will be the best option for you. However, don't be under any aspirations that it will perform as well as an equivalent aperture good quality newtonian. A good one will get close. They aren't all good however, I have seen several that were down right terrible.
As you correctly point out, the main downsides to a SCT as a visual planetary instrument is the large central obstruction, usually 35% to 38%. This reduces the light gathering area of the telescope by between 5% and 10% but most noticeably affects the MTF curves and contrast. There is an enormous amount of literature available on the internet about this. One of the best references on it is "Star Testing Astronomical Telescopes by Dick Suiter". Traces of the MTF curves show that at the lower spatial frequencies an obstruction <20% has little effect on image quality but an obstruction over 30% has a noticeable effect.
There is an excellent free program called aberrator you can download where you can use real planetary and lunar images and see the visual effects of a change in central obstruction on the image. You can also use this program to see the visual effects of other aberrations
In addition to the effects of Central Obstruction the SCT design can be noticeably affected by cooling and thermal equilibrium issues, which affect the higher power views.
You then have the additional surfaces involved which reduce light throughput and through the effects of diffraction and other optical aberrations, reduce image quality. They are all only minor but they all add up. You have a corrector plate additional to a newtonian and you have a star diagonal additional to a newtonian.
All the above having been said, I am sure given your requirements a SCT or ACF design is likely the best option for you.
While I agree with everything John B said from a technical standpoint, I only see two really significant problems with SCT's, those being cooling and the chance of getting a bad sample.
The vents on the EdgeHD scopes will make cooling easier to accomplish.
Light throughput isn't an issue with modern coatings. My C11 XLT is brighter than the less than 2 year old 10" GSO dob it replaced. I reckon a dob with standard coatings and an XLT/UHTC SCT must have very similar transmission on an inch for inch basis.
My viewpoint on SCT's Vs the newt is exactly the same as johns. I looked at Perth observatories 14" meade SCT on M83.... I was more than dissapointed i looked at the scope and went what a POS..... my 10" f4.7 is clearly able to resolve the dustlanes and fine details in the arms. the 14" was barely able to resolve there was a galaxy there other than a smudge.
Photography possibly but you better have some damn fine skills at guiding at f10! closing in on 3000mm FL, start really looking at Adaptive optics and a whole raft of other things. at 1200mm guiding is more forgiving and you don't need AO.... So still the 10" newt is in my opinion far superior in Value and performance.
Casstony, while i agree that the light though put and technologies are miles ahead of what they used to be a GSO/SW dob is what 500 bucks.? a XLT 11" is 5000. Where as a Orion optics CT10" with 1/10 PV ultra grade optics is possibly 3500 once imported.It weighs less than a SCT, gives far brighter and far more resolution than a SCT and for astrophotography will do some increadable things see Mike Sidionios 12 AG... same optics. Compare apples with apples not Hyundai's with Farrari's
Ok Brendan, I am showing my "newbie-ness" to astro-photography here, but I want to understand the effects of focal length on ease of imaging.
The C9.25 and C11 EdgeHDs come with Fastar/Hyperstar compatibility. So you can image at F10 or F2.
My assumption is that if I cheat and use a webcam and stack the frames I should be able to get some pretty reasonable shots of planets at F10 without need for guiding, no?
For DSOs, I would use the Hyperstar setup and something like the QHY8 camera which is very small in diameter. Since I would be working at F2, can I get away without a guide scope? Now since the focal length would then be reduced to something like 22 inches, wouldn't the DSO being imaged be just a tiny dot? If I had a very high resolution camera that might be OK, but I won't be able to afford that - or is there some other trick to this?
Otherwise my preference for a higher level of astrophotography would be to buy a nice 4" triplet fast refractor later down the track when I have more time (ie kids all grown up!).
Unfortunately people try to get a Catch All Scope. it just doesn't happen, the hyperstar while a very good system and ive seen some really really good wide field work come from them are hard to collimate and unless your a confident tinkerer generally youll end up pulling your hair out.
Effects of focal length on ease and what not with imaging....
1. get a maccas straw or something similar. look though it youll notice if you shake a tiny tiny bit you see it in dramatic fashion!
2. get a A4 piece of paper and on the long edge roll it around stick some tape on it (make the biggest tube you can with the paper). Look though if you shake you really don't see it.
That in a nut shell is the difference between focal lengths to visually understand whats happening.
So when you are guiding at a long focal length small movements of the scope equal large guiding errors
When you are guiding at a short focal length small movements of the scope equal small guding errors
Atmospheric disturbance affects image clarity because of the same as above. star moves alot in long focal lengths hence the AO is used to "bend" the starlight to achieve a rounder star.
Short focal length the atmospheric disturbance "wobble" is not noticable as it is under the celing of your scope/cameras resolution
SCT's Suffer Mirror flop and you need to do all sorts of things to sort this out not so easy. Cooling like has already been said is a pig and you will be waiting a whole lot longer than the comparable newt.
There are what i distinguish as two types of astrophotographers. Im not bias to either and im not fussed if you are one or the other but they fall into the catagory of;
1. I just wanna take a happy snap I don't care how good it is im pleased with anything
2. Guys like Mike sidionio, myself, Grahame, Martin etc etc that are always pushing the envolope and striving for crisper clearer images.
if you fall into catagory 1. sure don't bother guiding jsut take a 30 second exposure and be happy. If your in number 2.... Guide the technology is there use it.
Amature fork mounts are less than average when it comes to astrophotography (professional ones are very good)
GEM's are for newtonians and amature varients are extremely good.
As for refractors vs newts at the end of the day its going to come down to what you like to image and im sorry but you will not know untill your trundling around going what am i going to image, it may be a galaxy you want, or it may be a large diffuse nebula or even dark nebula. sure one telescope can take the image.... but the other will do it 10x better. I like nebula mostly and large galaxies my FOV is perfect and the large mirror is essential as a addition a large format CCD which wont be too far away for me and that will make it sweet for my preferance!
Casstony, while i agree that the light though put and technologies are miles ahead of what they used to be a GSO/SW dob is what 500 bucks.? a XLT 11" is 5000. ..... Compare apples with apples not Hyundai's with Farrari's
I was comparing what I'd owned and used Brendan. In my particular observing conditions the C11 provides better DSO views due to greater light gathering which I can filter more severely, even if the 10" dob was sharper.
While a newtonian in general will produce a better image than a SCT, I feel you're being a bit one-eyed and exaggerating the differences .
Considering the original question concerned SCTs, this thread has certainly digressed to the point where it could be misconstrued as being a case of...............
All scopes are a trade off in one way or another. If we really were worried that much about pure optical perfection we would move to the desert and sell up everything we own. I think the original question has been answered, I hope you get a lot of enjoyment out of whatever you choose, and the offer is always open to borrow one of my SCTs to find out if you will get out of it what *you* want.
