Duel - Orion USA ED100 vs Celestron C8

[russ]

Last night myself and Ant got the chance to do a direct comparison between the ED100 and Celestron C8.

Conditions were poor, actually they were very poor. A combination of high cloud, mist and light pollution. Only really one object worth trying...Saturn.

We setup the EQ6 and first scope on-board was the Orion ED100. The Orion is a 100mm f9 refractor with an air-spaced doublet lens, with one element of FPL53 glass. It's the FPL53 glass that makes all the difference. Although whether that makes it a Semi-apo or a full apo is open to debate. But it's definitely not an achromat.

We used various eyepiece combinations, all with an Orion 2" enhanced mirror diagonal. All the eyepieces gave a nice image but it was the Vixen Lanthanum 5mm that most impressed. With the Lanthanum in place, the ED100 gave a superb bright, contrasty and pinpoint sharp image. Cassini's devision was a very well defined black line deviding the rings. And on the planet's disk we could see a wealth of detail due to the superb contrast on offer. And Saturn showed a nice colour too.

There was not even a hint of chromatic abberation with ED100, it's incredibly well corrected.

The crayford focuser has a nice smooth action with absolutely no image shift. It's not a patch on the William Optics Crayford fitted to the Antares Sentinel mind.

Onto the C8 then. May i just say that before we hooked up the C8, Ant refused to believe that the ED100 would have a hope against the C8.

The C8 is an 8" (203mm) f10 SCT with Starbright coatings. It uses the usual SCT method of focusing, which is moving the primary mirror to reach focus. This has pro's and con's, which I will explain later.

So onto Saturn then. Well the first thing that strikes you when looking through the C8 after the ED100, is just how much brighter the image is. And the increased image scale. Both of which you would expect taking into account the ED has half the aperture and less than half the focal length.

The next thing that strikes you is the focus action on the C8. It's smooth but there's plenty of image shift. This becomes very annoying at high magnifications, and especially annoying when imaging. I do have a Crayford focuser which screws onto the visual back of the C8 but we didn't use it for this test.

The upside to the C8's (or any SCT) focuser is the huge focus travel. Just about any eyepiece or accessory can be brought to successful focus without any problems. It's a huge plus point, especially when compared to the woeful focus travel of your average Newtonian. It also has to be pointed out that image shift doesn't just afflict SCT's. Most, if not all, Newtonians and refractors that use low grade rack & pinion focusers also have this affliction.

So how did Saturn look? Well it was bright and large. Quite sharp, Cassini was no problem. Hmm but where's the contrast? Well contrast in the C8, and it's Meade equiv is very poor. Surface markings that were so easily seen in the ED are nowhere to be seen in the C8. And the nice colour has gone too. Could definitely see one band easily but that's all.

To be fair to the C8, I've seen Saturn look far nicer than this on better nights but on those nights the ED was mesmerising.

I think by now you should already know the verdict. A very easy victory for the 4" refractor. In short, it completely destroys an 8" SCT. Which comes as no surprise really because my previous duel, Intes-Micro M603 vs Meade SCT, had the same result. And the ED is better than Intes 603.

The SCT is great all rounder but when faced with a more focused type of telescope it's flaws (and pretty major at that) become all too apparent. That all said i still love the SCT, it's a great telescope design. It's small, lightweight and very easy to use. In isolation, it's planetary views are good and even compare well to a fast Newtonian. It's deepsky performance is excellent. It's a great imaging device. And i've already mentioned the superb focus travel.

Really only three things let the SCT design down:

Cool down time

Image shift

lack of contrast

By comparison the ED100 is a gem in almost every respect. It's lightweight, very quick cool down, zero image shift focuser, superb for imaging, jaw dropping views of the moon, wonderful views of the planets and amazingly tight and round stars.

It's single drawback is lack of aperture for visual deepsky work.

If you ever get the chance to own a Skywatcher or Orion ED100, take it!

Regards

Russ

[OXO]

Great review and report Russ something of a suprise to me i really didnt think the ED100 would have a chance against the C8 maybe expect nicer view's at low power but at high Mag thats's quite something isnt it :shock:. The C8 is one of those scopes i have always fancied owning in the past just love the look of them and there compactness for the size Mirror you get but after reading this maybe the ED100 should be higher up on the wish list.

Can i ask what is the lengh of the ED100 i guess it must be quite long being F/9 this would be the only downside to owning one for me at least those uncomfortable observing positions etc etc but thats just me.

Cheers

James

[GazOC]

Russ,

Your findings square with my experience of SCTs on planets, I had my (our!!! ) 127mm Mak side by side with my LX90 and the Mak was slightly better alround and def. better image contrast when oberving Mars.

If course on DSO's the aperture of the SCT will be hard to beat.

Gaz

[GazOC]

Russ,

Your findings square with my experience of SCTs on planets, I had my (our!!! ) 127mm Mak side by side with my LX90 and the Mak was slightly better alround and def. better image contrast when oberving Mars.

If course on DSO's the aperture of the SCT will be hard to beat.

Gaz

[russ]

James, Don't worry about awkward observing positions because they seem to have balanced the tube a lot better. Unlike the old Evostars where you had to lie out on the floor to use it, the balance point on the ED is somwhere close to centre of the tube. It's shorter than 102 and 120 Evostars anyway, which both have 1000mm fl.

Gaz, you're right it's not really a surprise. SCT's are renowned for their poor contrast. But they strike quite a good balance for planets/deep sky.

Russ

[russ]

I also forgot to mention that we pushed the Orion ED all the way 300x using a 9mm Ortho with TV Powermate 2.5x and the image was a bit dim but otherwise nice. Best view was with the Lanthanum 5mm at 180x. Super sharp, bright and loads of contrast.

Regards

Russ

[GazOC]

Yes Russ, I can see the atttraction of SCTs- you can have a 200mm f10 scope thats only ~18" long. Easy to tansport and easy to mount for the size.

[Saso]

Great review. It would be interesting comparison in deep sky objects if you can observe together in better night. On some dimmest clusters, nebulas and galaxies.

Saso

[FLO]

I think by now you should already know the verdict. A very easy victory for the 4" refractor. In short, it completely destroys an 8" SCT.

Thanks for a very interesting report Russ.

Two questions please:

What eyepiece were you using on the SCT when comparing the view of Saturn?

I accept that the four inch refractor has more contrast but, what about actual definition (when viewed at the same magnification)?

Thanks,

Steve

[russ]

Hi Steve,

We were using a 5mm Lanthanum on the ED to give 180x. We did push the ED to 300x and it held up very well indeed, just a very dim image.

And we used the 15mm Antares Elite (133x) and the Celestron 9mm Ortho (220x) with the C8. The 5mm Lanthanum would have given 400x on the C8, way too much for such poor seeing. Especially as the C8 was having trouble at 220x.

Contrast and definition were both better in the Orion. Cassini was so well defined in the ED, where as in the C8 there was no mistaking Cassini but it lacked any bite. Certainly didn't look etched with a black magic marker like the ED. The same applied to the planetary detail.

We tried to match up magnification best we could but we were never going to get them exactly the same.

We also wondered whether the C8 was more adversely affected by the poor seeing. I've certainly had very nice views through the C8, far better than viewed on this night..

I would like Rob to take part next time, be nice to get his view. Especially as he rated the Intes so highly, be interesting to see how he thinks the ED and C8 compare.

I'll run a part two of this when Jupiter improves. That'll be a true test of definition, resolving power and contrast. Just how much planetary detail can each scope pull out. See If i can get Rob to include his Mak too.

Would also like to take the ED to my local club and compare it to the Tak Sky 90 and FS102. Perhaps this Saturday? I'll report back if i do.

Russ

[Ant]

I was very suprised that the ED100 beat the C8 - but apart from the image being brighter in the C8 - all other aspects were an easy win for the ED100.

All in all a good night and a good test of the scopes.

Ant

[FLO]

Okay! I've tried to be grown up and bite my tongue but tonight ... I failed.

The 4" simply cannot be better than the 8". If it were, it would be breaking a fundamental law of optical physics:

More aperture = more resolution.

(Telescope type and whether or not it has a central central obstruction has more to do with contrast than resolution).

Don't get me wrong, I believe you; the 4" must have shown more resolution.

My question is: What was wrong with the SCT?

[GazOC]

Okay! I've tried to be grown up and bite my tongue but tonight ... I failed.

.

My question is: What was wrong with the SCT?

Steve, don't worry about it. We all have differing opinions, you don't have to be "grown up" to have an point of view on a type of scope.

As to your question: IMHO a 8"SCT wont beat a 4" refractor or a 6" Mak on planets and thats all Russ, Ant and myself have said?

[tom.yates]

MY 2P Worth 12" sct 5" apo the 5" gives more contrast clearer images than the 12" the 12" is brighter but thats about it the view through the apo is spot on you don't seem to get the same views through the sct even though they are still very good allrounders.

[FLO]

Thanks for your comments chaps but brightness and contrast are one thing, resolution is another.

When working on an image in Photoshop, you can pull more detail from a low contrast, high resolution image than one the other way round.

If we're saying a 4" refractor gives more pleasing images with 'bite', then I understand, perhaps even agree, but as much as I'd like to think otherwise a 4" aperture cannot resolve more than 8".

If the 8" did not resolve more than the 4" then either there was something wrong with it or my understanding of optics is wrong and I need to rethink?

Steve

[GazOC]

"Bite" is a good word Steve, certainly one of the things that I disliked about my LX90 was the lack of "snap" when focussing esp. on planets.

[OXO]

I think Sky conditions can be a big influence too as a smaller scope will often perform better than a larger scope this should also be considered IMHO.

Saying that if you have owned a SCT like Gaz and a Refractor or whatever then you can say which is better out of the scope's bigger aperture may sound like it should perform better but if you have 1st class optics in a 4" Refractor then the balance between the two is swayed if you get my meaning? thats my take on things..

James

[FLO]

...the scope's bigger aperture may sound like it should perform better but if you have 1st class optics in a 4" Refractor then the balance between the two is swayed if you get my meaning?

True James, though the 8" SCT does have an aperture twice the width and 4x the surface area of the 4" and Celestron don't normally skimp on their SCT optics.

Chaps, we keep discussing qualities such as brightness, contrast and 'bite' but what I would like to concentrate on is resolution/definition - the scopes ability to reveal detail.

Thanks,

Steve

[GazOC]

Where planets are concerned you can't just dismiss contrast when discussing planetary performance, have you ever compared an SCT to a Mak/Cass or a Newt, side by side? Theres just no getting round that lack of contrast, snap, bite or whatever you want to call it.

[CELESCOPE]

well i have listened to all this , so i shall have to run a little test myself now , using the 8 inch gps and my ed 80 , not looked through an eye piece in ages now, so should make for interesting viewing. well when its clear again that is .

will keep you posted

Rog

[russ]

Steve, i think you're getting confused between visual and CCD imaging. This was a visual test of the scopes. For imaging the SCT wins, without a doubt. The Toucam with can deal with a bright image by turning down brightness and gain, human eye can't.

I'm 100% happy with my findings. Also happy with the collimation on C8, if the collimation or the optics were Pete Tong, the images i produce would reflect that.

Just to make the point. On Saturday I went up to my local club. A night of deep sky was the plan. But with Saturn blazing, we couldn't resist rolling back the roof on the 14" LX200.

Of the 9 people there, not a single one of them said how nice the view was. And for good reason....it was an over bright featureless nothing.

Walk outside and view Saturn through Tony's Tak TOA130 and WOW. And not just the contrast or the bite, but the detail too. Totally breathtaking. And the Tak is easily able to punch above the 50x per inch guide. But best view on the night was 227x with a 2" Everbright, Type 5 16mm Nagler and 4x Powermate. We used the 2" Everbright and Type 5 16m Nagler on the LX200 to produce 219x. The TOA was giving away 9" in aperture to the LX200.

The thing is, what good is aperture and definition, if any details are going to be lost to brightness and lack of contrast. Aperture is not king when visual observing the planets. Aperture rules for deepsky visual but it falls down the pecking order for the planets. Telescope design and quality of optics move right up to the top of the priority list.

In short Steve, i agree with 100% that an SCT will be better for imaging the planets. And i disagree with 100% (not just contrast but detail too) that an 8" SCT will beat a good 4" Apo visually on the planets.

Russ

[tom.yates]

Got to agree with Russ had the 5" Apo out last night the views were astounding the sct that i have just can't live with the Apo

[FLO]

Thanks for your comments Russ,

I must have given the wrong impression...

Steve, I think you're getting confused between visual and CCD imaging.

No, I am quite clear on that which is why I make no mention of it. I am specifically interested in which of the two scopes produces more resolution.

The Toucam can deal with a bright image by turning down brightness and gain, human eye can't.

Agreed. But, if visually observing, a neutral density will lower the brightness to a comfortable level without harming resolution.

I'm 100% happy with my findings.

I am also 100% happy with your findings

Its just that I am curious enough to ask: How did the 4" beat the 8" on resolution?

The thing is, what good is aperture and definition, if any details are going to be lost to brightness and lack of contrast.

You can easily reduce the brightnesss from a large aperture scope by fitting a ND filter and still retain its ability to resolve detail. You cannot increase the brightnes or resolution of a small aperture telescope.

Aperture is not king when visual observing the planets. Aperture rules for deepsky visual but it falls down the pecking order for the planets. Telescope design and quality of optics move right up to the top of the priority list.

Agreed (I have not been commenting on their suitabilities)

In short Steve, i agree 100% that an SCT will be better for imaging the planets. And i disagree 100% (not just contrast but detail too) that an 8" SCT will beat a good 4" Apo visually on the planets.

If you check my posts, you will find that I have not been commenting about which scope best suits imaging/observing. If I had, I am sure that you'd find little to disagree with

Russ, everybody,

This is not about point scoring, thats not what I do.

This is not about brightness, contrast, ease of focusing, planetary/DSO observing or imaging.

This is simply a quest to know how a 4" scope can outresolve an 8".

Thanks for your patience,

Steve

[GazOC]

This is not about point scoring, thats not what I do.

Wheres that come from mate? :lol:

[OXO]

Yeah Steve don't think anyone here would think that way TBH mate