Long-focal length Newt or SCT

[osbourne one-nil]

Having spent most of my astronomical life with relatively short focal length instruments, I am looking for something a little bit different this time around. 

I have a T-Rex mount which can take a lot of weight, so I think the length of any tube will limit the scope before the weight. I am trying to decide between something like Orion Optics' VX8L (1200mm focal length) and a Celestron 8" SCT (I'd probably go for the Edge HD). I am only interested in visual and a definite preference for deep sky objects. 

The VX8L makes sense inasmuch as it's got enough focal length to allow me to get in close with the right eyepiece (my 9mm Nagler would give me around x130 and Cumbria doesn't often allow a lot more than that) but also allow nice open wide views with my 31mm Nagler, have great contrast, virtually no coma and not be prone to dew. The downside is the long tube might be a problem on any alt-az mount in terms of wind and pointing to the Zenith. I know I could shift everything forward and add some weight at the end to balance but then the eyepiece height might vary wildly, plus body heat can start to affect things at the business end. 

The C8 makes sense in that it's obviously much, much shorter physically, and weighs about the same. It gives more magnification with a given eyepiece which might be nice at times, particularly on planets and planetaries, etc. Ergonomically it should be far more comfortable to use. The downside is a very restricted field of view (even my 31mm Nagler will only give 1.25º) which might become really tiresome on a non-driven mount (although the slow-motion controls on my mount are excellent). It's MUCH more prone to dew (although I think this can easily be eliminated) and my only experience with an SCT before is not great; I found the views through my C6 nothing special at all. Finally, being a sealed tube, cool down and equilibrium might be a real issue. 

My head is still saying the C8 as the best compromise, but given my mount, what would you choose?

 

[ChrisLX200]

The Newt would offer the better visual experience I think, or another possibility would be a Mak-Newt which retains that 'refractor view' and can be pushed to stupid high magnifications. Downside of that is the weight, cool-down time, and it has the same propesity for collecting dew as the SCT (still controllable though).

ChrisH

[cs1cjc]

Orion UK scopes are light, so handling is easy even on the larger scopes.  Though above your budget, the VX10-10L on a dobsonian mount is the one I would go for.  At F/6.3, I would not want a coma corrector for visual use.  It is the longest instrument that is usable at zenith without a step, unless you are less than about 1700mm tall (5ft 7in), so it might cure aperture fever, or perhaps not.  I have a good Southern horizon so an equitorial mount is of no interest.  Push-to would be nice, though.  I would also want a curved spider of some kind, but might leave that as a retro-fit. 

If I were to be buying a made to order instrument, then I would expect any delivery date to slip.

[osbourne one-nil]

Thanks both - well there'd be no rush for scope as it doesn't get dark at night for about 5 weeks but both your answers confirm my suggestion that a Newt would probably be the most pleasing visually. I just need to decide whether a SCT outside will give better views than a Newt left inside because it's too heavy...if you know what I mean. 

I've got push-too on my T-Rex already so it would be like a Dob, only a bit higher up and with slow-mo controls. 

Hmmmmmm. 

[Stu]

Hi Piers,

It's a tricky one, I must say. I too have had negative experiences with SCT's in the past, but am getting the hang of them more now. I really enjoyed my Edge 8", didn't want to sell it and found it to be a very good compromise in terms of size, aperture, fov and cooldown. I had an AstroZap dewshield, plus I added a dew heater, you might want to try a combined heated one which would be better. I also added a Baader SteelTrack and SteelDrive as I did not like the image shift caused by the mirror flop. If you haven't had the pleasure, and are struggling to sleep tonight, have a read of my Devon Jollies report which was using the 8" and the Tak side by side. The 8" got more eyepiece time of the two surprisingly.

I'm currently experimenting with a loaned C9.25. It is lovely on Jupiter and higher power targets, but I definitely feel more constricted with the fov vs the 8". Everything is a compromise!

Cooldown is definitely an issue. The Edge optics block the baffle tube so you cannot use a cat cooler. There are after market fans which you can fit to the vents which I think would be well worth considering. My issue with SCT's is the fuzziness you get around brighter stars, they just don't seem to be as sharp as a frac. Much of this is related to thermal equilibrium, or lack of it though so it must be possible to get right. I guess alot depends upon where you will store the scope, how long you can give it to cool and whether you tend to have long sessions or shorter smash and grab ones.

I have tended to favour the view through newts recently. They just seem less susceptible to cooling issues, or rather are easier to cool. Collimation I would say is actually easier on an SCT, and tends to stay put more. The shorter OTA length will definitely be a bonus on your mount though.

I would keep and eye on Derek's thread on his OO VX12 f4 purchase. This is to be used on an AZEQ6 so although a generally beefier setup may give some pointers about a longer newt on an Alt-Az mount.

Just to add to the confusion for you, I looked through quite a few different scope types at SGL11, most of them pointed at Jupiter. What struck me actually were not the differences but the similarities of the images. Most, if not all of them were producing very nice views which I would have been happy to observe with! No help at all, sorry!

Sorry for the rambling thoughts.....

Stu

 

[Stu]

12 minutes ago, cs1cjc said:

Orion UK scopes are light, so handling is easy even on the larger scopes.  Though above your budget, the VX10-10L on a dobsonian mount is the one I would go for.  At F/6.3, I would not want a coma corrector for visual use.  It is the longest instrument that is usable at zenith without a step, unless you are less than about 1700mm tall (5ft 7in), so it might cure aperture fever, or perhaps not.  I have a good Southern horizon so an equitorial mount is of no interest.  Push-to would be nice, though.  I would also want a curved spider of some kind, but might leave that as a retro-fit. 

If I were to be buying a made to order instrument, then I would expect any delivery date to slip.

I had a VX10L f6.3 1/10th wave OO Dob for a while. Lovely scope, as you say no need for a coma corrector and gave excellent view of quite a range of mid to high power targets.

[osbourne one-nil]

Thanks Stu - I've actually got a lot of people waiting on me for a lot of work today so I might read your holiday blog now to take my mind off it all!

Interesting what you say about most of the views looking broadly similar. If that's the case, then at the moment, the SCT would make more sense for me but perhaps the Edge wouldn't be worth the additional cost. 

Do Seben do an 8" apochromatic refractor which weighs 4kg and costs £199? I'll have a look on eBay. 

[John]

My only input is to suggest that you think carefully about the impact of tube length on the mounts ability to hold it steady. I know that the T-Rex is a very capable mount but don't underestimate what forces a long tube can inflict regardless of it's weight !

[Stu]

25 minutes ago, osbourne one-nil said:

Thanks Stu - I've actually got a lot of people waiting on me for a lot of work today so I might read your holiday blog now to take my mind off it all!

Interesting what you say about most of the views looking broadly similar. If that's the case, then at the moment, the SCT would make more sense for me but perhaps the Edge wouldn't be worth the additional cost. 

Do Seben do an 8" apochromatic refractor which weighs 4kg and costs £199? I'll have a look on eBay. 

We can wish

Have you thought about a dob Piers? My 10" dob was relatively light and easy to move around. The dob mounting is much steadier than an Alt-Az too, for a long heavy tube anyway.

You could also consider an EQ platform if you want tracking.

[cs1cjc]

Just a few more points in a new post since I have already edited my earlier post too often:

* Dobsonians take up surprisingly little storage space;

* I would probably specify a spider of this form: Royce_Curved_spider or perhaps a straight 3-arm spider and then retro-fit the curved one.

* I would reverse the fan direction and make a baffle for the back so air flows down the tube, past the mirror rather than coming in at the back;

* I would probably mask the outer 2mm or 3mm of the mirror;

* I would fit a stainless screw pipe clamp to allow the tube to be rotated;

* I would fix a removable flexible dew shield with velco.

That is all, I think.

[osbourne one-nil]

11 minutes ago, John said:

My only input is to suggest that you think carefully about the impact of tube length on the mounts ability to hold it steady. I know that the T-Rex is a very capable mount but don't underestimate what forces a long tube can inflict regardless of it's weight !

That's a fear of mine, although spending £300 and finding it's not quite right is a lot easier than spending £800, although both are rectifiable (at a cost) by selling on. 

I have thought about Dobs - have been there before very recently with a Portaball, but there are a few issues there. I'd be loathed to sell the t-rex ever as it would be very difficult (and expensive) to replace in the future. I wouldn't need to sell it to fund a Dob, but it would seem a bit of a waste to me. I really like it and paired with a Nexus DSC and a tablet, it's so much fun. I know I can get push-to and even go-to dobs, but I'd miss the link-up with planetarium software. Another thing is ergonomics - I just prefer observing standing up and an alt-az mount seems to make that more achievable with medium-aperture scopes. 

Of course, I might get a 12" dob for the same money as an 8" Edge HD. 

[Linda]

5 hours ago, osbourne one-nil said:

My head is still saying the C8 as the best compromise, but given my mount, what would you choose?

 

I have recently made the choice and ended up with the C8. My main argument was that I like to sit behind the telescope and not to stand on the side on different heights.

I also thought that collimation with an SCT was easier than with a reflector and it should keep it's collimation better. When it comes to the field of view, I am used to a Maksutov, so it wouldn't be worse than that. I have installed a 50mm finder scope on it, as well as a Rigel Quikfinder, to make finding objects easier.

I haven't been able to use the C8 much because of the summer, but when looking at a planet, it is moving very fast out of view. I need to follow manually the whole time. If you intend to watch the same object for a long time, you should definitively install a motor drive.

[osbourne one-nil]

Thanks Linda - I'd concur with all that, I could, of course, get a driven C8, but then I lose simplicity of an alt-az mount with optional push-to. 

What on earth was I thinking pretending I could live with one scope!

[Stu]

1 hour ago, osbourne one-nil said:

That's a fear of mine, although spending £300 and finding it's not quite right is a lot easier than spending £800, although both are rectifiable (at a cost) by selling on. 

I have thought about Dobs - have been there before very recently with a Portaball, but there are a few issues there. I'd be loathed to sell the t-rex ever as it would be very difficult (and expensive) to replace in the future. I wouldn't need to sell it to fund a Dob, but it would seem a bit of a waste to me. I really like it and paired with a Nexus DSC and a tablet, it's so much fun. I know I can get push-to and even go-to dobs, but I'd miss the link-up with planetarium software. Another thing is ergonomics - I just prefer observing standing up and an alt-az mount seems to make that more achievable with medium-aperture scopes. 

Of course, I might get a 12" dob for the same money as an 8" Edge HD. 

Piers, you can quite easily have a push to Dob linked to SkySafari. I had that system on my Sumerian Canopus and it was brilliant. It had encoders and a Nexus fitted so all I had to do was connect to my phone, really simple and accurate.

[osbourne one-nil]

Ah - I was thinking I'd be limited to the Skywatcher or Orion (US) ones and didn't know how that would work. I'll have to look into how to get the encoders fitted to something. Luchtime reading. 

[swamp thing]

3 hours ago, osbourne one-nil said:

 

The C8 makes sense in that it's obviously much, much shorter physically, and weighs about the same. It gives more magnification with a given eyepiece which might be nice at times, particularly on planets and planetaries, etc. Ergonomically it should be far more comfortable to use. The downside is a very restricted field of view (even my 31mm Nagler will only give 1.25º) which might become really tiresome on a non-driven mount

1.25˚ is not a very restricted field of view at all. Very few objects are anywhere even near this size.......Just how much empty sky do you wanna look at?  

 

 

[Stu]

45 minutes ago, swamp thing said:

1.25˚ is not a very restricted field of view at all. Very few objects are anywhere even near this size.......Just how much empty sky do you wanna look at?  

 

 

I bet you get agoraphobia whenever you venture over a degree Steve

 

[osbourne one-nil]

51 minutes ago, swamp thing said:

Just how much empty sky do you wanna look at?  

 

 

1.26 degrees' worth is my minimum. I want everything of course, I want wide field and high magnification and no focal reducers or barlows. Easily pleased!

[Stu]

26 minutes ago, osbourne one-nil said:

1.26 degrees' worth is my minimum. I want everything of course, I want wide field and high magnification and no focal reducers or barlows. Easily pleased!

I've found the solution Piers, just don't have the cash! 

http://www.televue.com/engine/TV3b_page.asp?id=199

[osbourne one-nil]

Good gracious - it doesn't even come with a finder or a free star map. For that price you'd think it would. 

[Neil27]

I'm actually going the opposite way and prefer a wider FOV.

Again it is marvellous how this hobby can be ones persons food and another poison 

I bought a C8 Edge a little while ago but then quickly realised that my main interest of video astronomy would be better suited to a 'shorter focal' telescope.

Again mistakes are relatively easy rectified as I find astronomical gear very well looked after.

Apologies for hijacking your post but you do bring up a valid question and one that will get a different answer whomever you ask.

Kind regards, 

[John]

2 hours ago, osbourne one-nil said:

... I want everything of course, I want wide field and high magnification and no focal reducers or barlows. Easily pleased!

The nearest scope design that I've owned that ticked these boxes was a maksutov-newtonian. Mine was an Intes 6" F/5.9 and it performed pretty much exactly as well as a 5" apochromat refractor would. The slight downside with the design is that they are quite heavy for their aperture and take a bit longer than newtonians to cool. You need a good dewshield with them as well.

Maybe one of the 190mm mak-newts would be worth thinking about ?

[swamp thing]

3 hours ago, Stu said:

I bet you get agoraphobia whenever you venture over a degree Steve

 

I actually have a 4.5" rich field scope Stu, believe it or not   (I bet that shocked you). It just seldom gets used. (can't even remember that last time it saw star light).

I ought to use it a bit more really as its kinda fun to sit with it in my lap cruising the milky way. Small newts make great lap scopes as the eyepiece allows for sit and view. No mount at all just a carry strap to wander outside with it over your shoulder.  

[osbourne one-nil]

Thanks John, that really is worth some serious consideration. The tube's quite long again, as with a normal newt, but perhaps it's worth it for the pinpoint images and lack of coma. I keep reading reviews of the apo-like images, which is very tempting and it would allow me to indulge my lower-power mucking about with the chance to use some serious power too. I guess cool down wouldn't be too dissimilar to a SCT and the price is comparable. 

Hmmmmmmm.....again. 

[Stu]

2 minutes ago, osbourne one-nil said:

Thanks John, that really is worth some serious consideration. The tube's quite long again, as with a normal newt, but perhaps it's worth it for the pinpoint images and lack of coma. I keep reading reviews of the apo-like images, which is very tempting and it would allow me to indulge my lower-power mucking about with the chance to use some serious power too. I guess cool down wouldn't be too dissimilar to a SCT and the price is comparable. 

Hmmmmmmm.....again. 

I've always been quite tempted by a Mak-Newt, the MN190. I guess I've been put off by the weight and potentially the focuser which I think is supposed to be not ideal but I don't have any direct experience of them.