SCT & Newtonian shootout!

[philsail1]

Telescope Shootout! May/June 2009.

This summer, I’ve decided to try and do a comparison test of my two (excellent) scopes – mainly because I’m thinking of letting one of them go, as I’m finding the situation a bit stressful deciding which scope to set up for an observing session – especially as there haven’t been many clear nights this year so far. After setting up both scopes, instead of enjoying the evening, I’ve found myself constantly going from one scope to the other, thinking I might get a better through this or that scope. Trying different eyepieces, combinations of eyepieces and Barlow’s, Binoviewers, digital camera, etc, etc. Even trying the scopes on the different mounts I have!! Suddenly four of five hours have gone by – it’s 2.00am (and I have work in the morning!!). I thought, I must stop this silliness, bite the bullet and let one scope go – but which one?

The scopes:-

1. An Orion Optics (UK) 8” f4.5 Newtonian Reflector, with the "High Lux" mirror coatings, 8 point mirror cell support, a basic “Crayford” type focuser, and an 8x50 straight through optical finder scope.

2. A Celestron C8, f10 Schmitt Cassegrain Telescope (SCT). I do not know if this scope has the “Starbright” coatings as I obtained it second hand from another SGL member. It is fitted with a two speed ultrafine focuser, an 8x50 straight through finder scope, and more recently a camera bracket. The secondary mirror is fitted with “Bob’s Knobs” to aid collimation.

The mounts.

1. A Celestron CG5 “GoTo,” with the “Nexstar” star finding system. This mount is fitted with a Polar scope, built in bubble level, and has the 2” tubular steel legs. “GoTo” is powered by a “Powertank.”

2. A Celestron CG5 standard motor driven. This mount doesn’t have the fitted Polarscope. It has 2” tubular steel legs. It is powered by three “D” size cells.

I tried both scopes in observing the Moon, and the Planet Saturn, as well as some deep sky objects. Also, both scopes were tried using a variety of different eyepieces, (in combination with a Celestron Ultima 2x Barlow), and my “binoviewers.

The results of the Telescope Comparison were (in non technical terms):-

The Orion Optics 8” (f4.5)

For:- 1. Easily gave the brightest and most natural looking images – especially of Saturn.

2. Gave the most pleasing wide field views of the stars – especially when using a 2” 38x wide field eyepiece. (giving a magnification of 22x). Highest power the scope would cope comfortably with was 283x), although I tended to restrain my “high power” viewing to 170x. (10mm Antares Plossl with 2x Celestron Ultima Barlow).

3. Was the easiest scope to fine focus. (The focuser is Orion’s version of a “Crayford.” Although this is their “premium” focuser, it is not of the quality and smoothness of a “Moonlite!”).

4. No “image shift” during focusing.

5. Easier to find things in the night sky with the wide field of view.

6. Accepts a wide range of eyepieces, from inexpensive Kelners, to 5mm Vixen Lanthanum.

7. Tracks well (and is steady) on the CG5 “GoTo” mount.

Against:-

1. Was the hardest scope to handle when setting up – despite me having attached a lifting handle to the tube rings. I find it a bit fiddly to get the scope attached to the CG5 mounts.(Especially as these mounts have only one main securing bolt). The easiest method I have adopted it to position the mount so that I can put one foot on the actual leg of the mount and steady the scope against my leg whilst holding the tube with one hand. Tightening up with other hand. However, once attached, and the bolt tightened (and the small thumbscrew tightened), the scope felt reassuringly secure.

2. The Orion was also the most difficult to physically view things through. (Simply because the viewing position on a Newtonian is on the side of the scope). I often found myself having to slacken off the tube rings and swivel the scope around to get the eyepiece into a comfortable position for viewing. Perhaps one way of avoiding this would be to view objects in the vicinity of where the scope is pointing, and gradually track across the sky. This would then involve only a “gradual” adjustment of the eyepiece position. With the “GoTo” In my excitement at having “GoTo” I tended to move the scope wildly across the sky from the extreme South East, to the extreme North West! I will need to plan my viewing a bit more logically in future.

3. When using my Binoviewers, I had to remove the extension tube on the focuser, to enable the binoviewers reach focus. The focuser finger screws are quite small on the Orion, with very small heads that can be difficult to grip – especially with cold (or gloved hands).

4. There was some “Coma” visible towards the outer edges of the view. This didn’t bother me at all, but it was there – and was better or slightly worse, depending on the particular eyepiece I was using (the cheaper, wider field eyepieces tending to suffer most).

The Celestron 8” f15, SCT

For:-

1. This scope gave the most magnified views, just about coping with a magnification of 600x on the Moon! However, achieving a sharp focus at this power was very, very difficult indeed. So much so, that I removed the 2x Barlow which reduced the magnification to 300x, which is about the Celestron’s useable limit. Much more comfortable and enjoyable viewing was had at powers of 166x to 200x. Stars remain sharply defined almost to the very edge of field of view – even when using a 2” x 38mm wide field eyepiece.

2. Easier and quicker set up time. The tube on the C8 is much shorter (16” against 34”). Once located on the CG5’s mount, the scope’s tube could be held with one hand and tightened up with the other. Only requires one counterweight to balance scope.

3. More comfortable viewing position. The eyepiece always remains at the rear of the scope. If the eyepiece does get into any unusual angles, I can easily slacken the Williams Optics Diagonal and swivel the eyepiece back into a comfortable position.

4. Focuses very easily when using the Binoviewers. Much more comfortable viewing position using them.

5. Much easier to change eyepieces. The Williams Optics 2” to 1.25” diagonal is a joy to use. It has a single large thumbscrew which acts upon a brass compression ring. Holds even the heaviest of eyepieces (and binoviewers) in place without any worries of anything falling out.

Against:-

1. Long “cool down” time. Shaky views unless left for at least 45 mins. (This had me fooled when I first had the scope – I thought views were shimmering due to heat from surrounding houses).

2. “Image Shift.” At high powers, there is quite a bit of “image shift” to cope with. This is despite this particular scope being fitted with a “Feathertouch” dual speed rotary focuser. Sometimes creates difficulties when taking photographs. (I think a Crayford rack & pinion type focuser would eliminate image shift).

4. The views were not as bright, or natural looking as in the Orion. I seemed to detect a touch of “softness” in the views of Saturn. (I don’t think the scope’s collimation is out, as the stars are sharp pinpoints).

5. Narrow field of view. Although this didn’t impact much when using the wide field eyepiece, it did make finding things a bit difficult when using “GoTo.” When using the CG5 motor driven mount, I had to ensure that the scope was lined up accurately with the finder scope.

6. Difficult to achieve a sharp focus point. Although the “Feathertouch” two speed focuser has a lovely smooth action, it is still difficult to get a sharp focus. In my opinion, a rotary focuser just doesn’t feel right in ones fingers, whereas even a simple rack & pinion focuser instantly feels natural when using it.

Conclusion:-

Both scopes have their good and not so good points. Both scopes were satisfying and generally easy to use. (I think anyone owning either scope would be very satisfied with their optical and mechanical performances. (If I did not have the Orion Newtonian to compare, I would be more than satisfied with the Celestron C8’s performance). To be fair, I don’t think anyone could expect two scopes (of a totally different optical design) behave identically. Indeed, I think that the fact that both scopes performed so well in their own right, is making

letting one of them go, such a difficult decision. I’m erring slightly on the side of keeping the Celestron C8 SCT, mainly because it is the easiest scope to set up, has got the most comfortable viewing position, and it allows me to use my Binoviewers with ease. Also, I have just bought a camera bracket (from another SGL member), and I’ve ordered a Williams Optics 45 degree Erecting Prism diagonal, (from FLO) which will give me an even more comfortable (sitting down) viewing position.

Mounts.

Both mounts coped with the scopes weight equally well. However, Because there was a tiny amount of “backlash” in the motorised Celestron CG5 mount, the Orion Newtonian tended to show some movement if accidentally nudged. The CG5 mount was the easiest and quickest to set up. Also the CG5 was the easiest to use as far as adjusting the tracking to “centre” what you were looking at.

The CG5’s “GoTo” mount took longer to set up because certain details - date and time - had to be entered each time it was switched on. Although once set up correctly, it tracked equally as well as the CG5 none “GoTo “ mount. The only thing I found detrimental in the “GoTo” was the fact that if the mount was not set up very accurately to the Pole Star, and the object I was looking at started to “drift” slowly either up, or down, or from side to side. When I used the direction buttons to centre the object, it threw the “GoTo” out be several degrees when searching for another object. The only way I could centre objects without upsetting the “GoTo” system, was to slacken the axis locking levers and manually try to centre the object in the finder scope, then try and lock the levers without letting the scope move! Very awkward.

In this respect I found the standard motorised CG5 mount, by far the easiest to use.

Regards,

phisail1

[dweller25]

Great write up Phil - spot on.

[philsail1]

thanks "dweller25"

hope it may help someone.

Regards,

philsail1

[GazOC]

Interesting Phil, those are pretty much the same pros and cons I've always "seen" when comparing the two designs of scopes.

[Lee]

I really enjoyed reading the review.

Personally I believe you can't go wrong with "Quality, Fast optics" the best all-rounder I believe. Nice rich wide field views and with good optics they can take the higher mag. If it were my choice I would stick with the Newt, I recon they are going to make a big comeback this year... I wouldn't mind an OO newt myself.

Lee.

[mdstuart]

I am just jelous that you have two amazing telescopes. Which one can see the faintest stars have you tested them on some very faint galaxies. Which one shows M51 the best etc.

For me I think the wider field would win the day so the Newt for me...

Mark

[philsail1]

Yes, i can see your point Lee. I had both scopes out this morning, looking at Venus. And although I could not determine which was the better scope optically, I found that the Orion Optics Newtonian was able to "find" the planet much easier (with it's wide field of view) than the C8.

This is going to be a difficult choice for me to make in the next few weeks!

Regards,

philsail1

[Lee]

I think the other interesting comparison would be your C8i "V" the 90mm Mak?

You could have the Newt for widefield and the Mak will work well for the more contrast hungry planets. Just an idea... (I don't have anything against the Celestron by the way)

Lee.

[barkis]

You really are on the horns of a dilemma Philsail. Both have their merits and otherwise. I too feel I should unload one of my own units, but I don't let the thought dwell too long in my mind. I doubt I will in the long run.

There will be a decision lurking witin the depths of your minds inner sanctum, just let it surface naturally. No one can possibly make the choice for you, we wouldn't have the temerity to do so.

Best Wishes.

Ron.

[philsail1]

Yes, I will give your suggestion a try "Lee" as I do have a Skywatcher 90mm Mak upstairs in my back bedroom. I bought this one a couple of years ago and use it as a "super telephoto" lens (for my Canon A570IS digicam) on field trips doing "afocal" shots of wild birds. I could stick it on one of my tripods and see how it compares with the Newtonian on the planets. However, the main essence of the "comparison" I did between the two "big guns" was to try and reach some kind of "convincing," "conclusive," and "definite" decision as to which scope I would want to keep, and which one to let go, to get me down to one main scope! When embarking on an obesrving session, all I really want to do is have a clear mind when going to my shed to get my scope out and set it up. I just don't want to be faced with any dilemma of choice!

Yes, Ron, it is a real dilemma! I wish there was a "one scope fits all solution" (perhaps there might be somewhere!). I love the "natural" wide field views of the Newtonian, but the ease of use of the C8i pulls at me!

I posted the comparison with a secret hope that SGL members would make my choice for me, but I didn't account for the depth of knowledge you all have about various scopes, which resulted in your own comments on the merits of BOTH scopes!!

I think you are right in advising me to "sleep on it" and let a natural choice surface on its own.

I will do this Ron.

Thanks for all your advice - everyone.

Regards,

philsail1

[dweller25]

Hello Phil,

Have you looked at Saturn with the two scopes ?

If so did you notice a difference in contrast between the two ?

BTW - you have a great dilemma, Rons advice is sound - I would evaluate over a whole season as a scopes useability can change when the cold weather comes back.

Regards

[afm038]

Hello Phil,

A dilemma indeed, as the scopes are evenly matched whatever you choose you'll then have second thoughts and wish you hadn't made that choice !

I had a similar choice albeit mine were not so evenly matched as yours, I permanently mounted the SCT and kept the Newtonian as a "portable" scope so convincing myself to keep both - probably not what you wanted to hear though

Andy

[legion48]

If the Newt is the one to go, first dibs please.

[philsail1]

Thanks "Andy" and "dweller25,"

Yes, I have looked at Saturn dweller25 - and couldn't see a lot of differences in the views I got from both scopes. Some of the eyepieces used produced "subtle" differences in views between scopes. I think the overall impression I had was that the Orion Optics Newt seemed to give a more "natural" look to the planet. Also, the view was noticeably brighter viewed through the Newtonian. Of course, I had to use a shorter focal length eyepiece to get a similar magnification given by the C8i. Oh! and I've been trying both scopes out during the late winter and early spring of this year - but suffered dewing up problems with both scopes (the C8i dewing up the quickest!), before being able to evaluate fully the differences in performance during colder months.

No, Andy, it's a nice idea you give but I'm afraid one scope has unfortunatley got to eventually go!

Thanks again for all your input on my "dilemma." It is useful to get some objective and informed opinions - from people who are not "emotionally" involved!

Regards,

philsail1

[PaulG]

Great review Phil

I enjoyed reading through it.

Out of the two when cooled down, which gives the most stable view and maximum clarity of say the planets and Moon. I only say this as my Refractor resolved more detail and held it for longer than my Maksutov.

It's a difficult call to make to let one go.

I had to make that choice recently, even now I'm not so sure of my decision dam it wish I could keep a telescope collection.

My ultimate decision was based on pure visual performance of the telescope over weight and ease of use (which is a lot easier when you only look at the Moon & planets).

Paul

[philsail1]

Hello Paul,

Thanks for your comment.

Re stability and clarity of image after cooldown.

Difficult to say which one was best as they both give excellent images. C8i definately took the longest to cool down.

I would say the Newtonian actually gave me the "nicest" looking image. There was this kind of "naturalness" about the image in the Newtonian. Image appeared "cooler."

Image in C8i looked a tad yellowish (and this is exagerating really, but there definately was a difference).

Yes. a difficult one really!

Regards,

philsail1

[Deneb]

Keep the Newtonian, rich wide field views & thats a fast scope for imaging if your into that. Only because I recently got given a free LX10 OTA - F10, it seems it was not looked after properly just have to get some Bob Knobs for it, it's way out of collimation, I've heard collimating SCT's are not so straight forward as Newtonians.

I don't think I will be keeping it because I have to spend more money just getting the scope to be used for Deep Sky imaging.

[mike bacanin]

Hi Phil,

great post! btw you mention the sct producing sharp stars at focus.

did you check the inside and outside of focus diffraction rings?

even a very slight sct miscollimation can soften planetary detail.

A good C8 can show impressive detail in perfect collimation with a good eyepiece.

Mike

[philsail1]

"Deneb" you put a convincing point across there! I am going to do some more testing before making my mind up. I'm going to do some "Afocal" Astro photography with both scopes when weather improves, and make some comparisons - and perhaps post a few of the results on the imaging threads on SGL.

Mike - mmm, I haven't really checked the collimation for some weeks now (since I took the scope apart to paint the tube white). I collimated it after putting back together, and on checking it against the stars - using a high powered eyepiece, it seemed to show pretty regular concentric diffraction rings, inside and outside of the focus. I will check it again on my observing session (when clouds clear!). It could indeed be out of collimation. (I've been whizzing the main mirror fully in and fully out of it's focus travel when using the binoviewers and then swapping back to a single eyepiece - would this sort of movement put the scope out of collimation?).

Regards,

philsail1

[mike bacanin]

Phil,

I've done the same thing with a C9.25, i don't recall the collimation being affected to any degree to be an issue. What moving the mirror through its full travel does is spread the baffle tube grease a bit more evenly, resulting in smoother mirror travel.

It'll be interesting to hear if it has held collimation since last time.

Mike

[ollypenrice]

What about the fogging up of the SCT corrector plate issue? Do you have this problem?

Olly

[philsail1]

Hello "Olly,"

Yes, I experienced a bit of it ("fogging up" of the corrector plate) during last winter. This also became evident (to a lesser degree) on the Orion Optics Newtonian at times during the winter months. Also , I noticed that somtimes there was a bit of fogging on the outer edges of the main mirror on the SCT too.

Regards,

philsail1

[gliderpilot]

I think the answer comes down to whichever feature/benefit do you value the most:

Quality of views versus ease of use.

Mark

PS I wish I had to make a decision like this!

[Bigwings]

Nice review but can you advise me as to the effect of a 6.something reducer on the SCT. Would this give some of the good points of the Newt and does thatn have a bearing on which scope is the best allrounder to keep.

I ask as I have an 8" SCT and am thinking of a reducer for visual use but am not experienced enough to fully understand the pros and cons.

[philsail1]

Mark - well, I got myself into this situation by spending rashly! (which will inevitably cost me!!).

The biggest sacrifice I would be giving up if I let the Newtonian go, is the lovely bright and wide field views. However, I am leaning towards the "ease of use" issues, in which the C8i scores over the Newt. I'm desperately waiting for this awful weather to clear so I can give each scope's attributes some further scrutiny.

"Bigwings." I'm afraid I cannot really help you as I don't have a reducer for my C8i. I'm in a similar situation to yourself in that I've been thinking of getting one - a 6.3 reducer, but with me already having a 38mm 2" wide field eyepiece, I fear a reducer might not give much improvement on brightness, or field of view.

Perhaps another member will spot this and give us both some advice!

Regards,

philsail1