SCT vs Newtonian dob

[mac]

Hi guys and gals,

Another newbie gear question from me:

Is a Newtonian reflector better/worse/equal to a Schmidt-Cassegrain?

So far, my research has indicated that a Newtonian will equal, or even outperform a Schmidt-Cassegrain inch-for-inch, but is limited by its physical size and higher maintenance requirements.

The reason for my question is that I may have an opportunity to buy an 8" SCT on a mount with a clock drive for the same price as a 10" dob-mounted newt. I'm wondering which to buy...

-Matt

[stephenb]

Hi Matt,

I won't get into the comparisons with the optics and focal lengths, that will be for others to give you some good advice.

What sort of observer are you? or want to be? Naturally, the SCT with a drive will be an advantage for imaging, but more importantly it will help you keep track of you objects as you observe for a longer period of time. With a Dob you will have to manually keep the object in the centre of field of the eyepiece. But if you think you would like the challenge of Messier marathon's and location many deep sky objects in on evening, then perhaps the 10" Dob.

Just my 2 bob's worth..

[mac]

Thanks Stephen,

At the moment, I'm mostly wanting to do visual observing, with an instrument that can challenge me and hold my interest. In the past I've owned a 60mm refractor and a 5" reflector and they just didn't have the light gathering power to make me go 'wow'.

DSO's are something I'd really like to get into observing. Photography would be great, but this is not likely to happen anytime soon with my limited budget!

-Matt

[stephenb]

My gut feeling, mate, is to go for the 10" Dob.
How's your star hopping skills? and how's your night skies?

[mac]

My knowledge of constellations and navigating the sky is pretty basic, but I have Stellarium now, so I can just take my laptop out with me when observing (or at least study up first). :)

[marki]

The newt will deliver better contrast as the secondary obstruction is smaller. It will also deliver a wider field of view due to the faster optics. The SCT will deliver a better corrected field (less coma) but by no means perfect as coma still exists on the edge of the field of view and you need to add a reducer/flattener to get the most out of them for photography. The major disadvantage of the newt on a EQ mount is its sheer size (they are big) and the tendency to take a while for the vibration to settle and the position of the focuser which may require some sort of stool or ladder to reach when pointed high in the sky depending on the size of the scope and your height. The SCT has folded optics which make the tube compact and the light exits at the back of the scope allowing a comfortable viewing position. SCT's also have a decent amount of back focus available due to the moving primary mirror but this is off set by mirror flop on scopes without mirror lock. Newts tend to need modification or extra bits and pieces to bring a camera into focus. What you buy really depends on your targets. The newt will eat the SCT for some applications whilst the SCT will win for others. Best buy both :P.

[Mike21]

I don't suppose you have a vested interest in the Kiwis buying the Chinese out of the recession do you Mark?

[marki]

No, I don't think they have enough money ;). I have refractors, reflectors an SCT and a mak. I use each according to what I want to look at. Sometimes I set them all up and run between them:P.

Mark

[Mike21]

Sounds interesting. You must learn observing skills more quickly if you can look through so many scopes per night. Sounds like you have a greater investment in mounts than scopes.

[mac]

If I moved to Australia then I could afford both... :p

[Rodstar]

Hi Matt,

I can answer as someone who started off going the SCT route, and have since gone over to the "dark side" by getting a dob/newt.

I LOVED my SCT. It was a great scope to start out with in this hobby because it makes the location of objects so incredibly easy with the built in computer. Mine was a 10 inch LX200 (meade). It was very comfortable to observe with using an hydraulic stool. In those early days I particularly enjoyed discovering the many beautiful open clusters and colourful double stars that inhabit our southern skies, as well as some of the brighter globs and emission nebulae.

It became evident to me within a year or two, though, that the image brightness of a 10 inch SCT is not quite up to that of a dob. The difference side by side is quite noticable. This is a non issue for the brighter targets, like Jupiter or open clusters etc. However it does make a significant difference if you want to hunt down fainter fuzzies. This is where a newtonian comes into its own.

The lack of in-built computer with a dob can be rectified without too much angst with the assistance of an Argo Navis. If you include encoders and cables etc, this may add about $1000 to the cost of a dob, but it will make the dob just as able to track down targets as an SCT.

I think the most important consideration early on in this hobby is comfort. You should prioritise getting a scope that you are comfortable using, and which will get you out of the arm chair and out into the night air. For me, early on, an SCT achieved that purpose, and I became soundly converted to observing. Now I don't mind the discomfort of scrambling up a ladder and hauling around a large scope. I might not have been so keen now had it not been for my beloved SCT to begin with.

Hope that sheds some starlight....

[andrew2008]

Wondering if it would be possilbe for you to expand on which applications work better for newts and which for SCT's.

[mac]

Rod - thank you! This is exactly the sort of wisdom I was hoping to be passed.

So, I think I'll stick with the original plan to get a newt dob.

The argo navis will be high on my wish list, but since my wife only allocates me $40 per week 'spending' money (yep, tough times), it'll take me a year or two to save up for that.

[marki]

Rods pretty much nailed it except I can see dim objects well in my 10" LX200R :shrug:. Must have good eyes or dark skys not that I do much visual except when running astronomy nights at school. A CCD camera will always show more then visual. Newts give a sharper image with more contrast and a wider field of view. If you want to look at something big they are great as they have a wider field of view so you can take it all in in one hit. The object will appear brighter through any given EP because of the faster optics but will be smaller. I would use a SCT over a newt for photography as they are more stable on the mount although the long focal length can be a hassle at first. Best to add a reducer and take them down to about F6 - 7.

Michael, the ETX and LX200 have their own mounts. I bolt the refractors on top of the LX and have a HEQ5 pro to which I mount an old 6" newt. It works well on astronomy nights at school as I set the diagonals of the refractors so the EP's point out both left and right which means I can keep 3 kids busy using the same mount.

Mark

[coldspace]

Matt, Depends on your light pollution.
I have owned several dobs upto 12 inch in Suburban situations and they were good but really shined under dark skies.
Most of the time I was at home in moderate light pollution and did ot have much time to get out to dark skies so I got a 12 inch SCT and put a Mallincam on it.

If you can buy a good condition 8inch SCT for the same price as a 10 inch dob then thats what I would get.
Tracking and goto will make you enjoy observing alot more and in a moderate to worse light pollution environment having goto will be good and tracking will help you tease out fainter objects while staring in the eyepiece.
Sure, large dobs are great but for learning go the 2nd hand SCT for the advantages above unless you can afford a much larger Dob with Argo Navis attached to it.

With the SCT you could always attach an Astrovideo of somesort like Mallincam or G-star and then you will see most things in light pollution way better than a large dob in pristine dark sky especially if you plan to use it the most in light polluted environments.

Either option that mentioned will work but for the same price go for the SCT .

Regards Matt.

[mac]

Hmm, some compelling thoughts there, coldspace - thank you. I guess I'll have to mull it over some more. The SCT scope I'm looking at doesn't have GOTO, so I'd still have to hunt for objects myself. But the tracking on it would make a difference once an object is located...

In terms of astrophotography, I'd love to get into that - but just couldn't afford to buy all of the equipment involved.

[astro744]

Finding something can be just as rewarding as actually looking at it and sometimes even more so. You don't need GOTO but if you should want it later then encoders for the Argo Navis could possibly be added to the SCT to give you Push To. Astrophotography is easier with the SCT since you already have the tracking and perhaps add a focal reducer or tele-extender depending on what you want to image (neither essential for good lunar shots).

I have been a 10" Newt Dob owner for many years and recently got a C9.25 SCT and it is now my primary observing telescope mainly for the tracking ability and seated viewing comfort. The Newt Dob wins on widefield low power performance and ease of moving from object to object but I can take more of the image in simply by having tracking. I was getting a fantastic Jupiter last night that stayed in the middle of my eyepiece in my SCT and I'm sure the Newt would have given perhaps better contrast but at 200x the image just moves too quickly and even a Nagler soon runs out of field.

For equal dollar I would go the SCT now. You can always add a Newt later since their new costs are relativey inexpensive compared to new SCT costs.