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#1 js1976

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Posted 10 May 2013 - 04:18 PM

The last post I posed the typical newbie question as to which type of scope to buy. The overwhelming response was a Dob. How would most of you compare the Celestron Nexstar series? I kind of like the Go To feature and was looking at an 8 inch

#2 Paco_Grande

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Posted 10 May 2013 - 04:50 PM

8SE is an excellent choice for many people. Hard to go wrong. Holds its resale value very well also.

Just keep in mind that you need a battery unit and that an SCT requires a cool-down period or it won't perform well. They work well with moderate and lower priced eyepieces, which is not always true with Dobs (depends on focal ratio.)

SE6 or SE8 uses the same mount, so both are a fine choice. If you can swing the extra for the 8, go for it.

#3 Pharquart

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Posted 10 May 2013 - 06:07 PM

I've had a Celestron 8" SCT for many years, and recently purchased the SE mount for it so I'd have GoTo. I also have a 10" Dob, so it's easy for me to compare your options directly.

The GoTo is a great feature, especially for a beginner. However, as stated above, the SE mount draws batteries down quickly. I use a powertank to feed mine. So the setup process for the 8SE is more involved (tripod, OTA, power supply, cables, etc.) By comparison, I can be looking through my Dob in a few minutes. And with the SE mount, if you forget your power cord (or it breaks, or the fuse blows, all of which have happened to me) you're stuck. There's no manual option to point. It's motors or nothing. The Dob is all manual.

Both Dobs and SCTS require a cool-down time. It's longer for SCT scopes. But that doesn't mean you can't use either one right at setup. Your higher power views will "swim" more until they hit thermal equilibrium. But you can absolutely use both right away.

SCTs have a longer focal length (1500MM or 2000MM, depending on 6" or 8") compared to a Dob (most end up at 1200mm). So the SCT is better for high power (planetary) and the Dob is better for low power, wide views (star clusters).

Both are great first scopes. Pick which features you like best! And in the end, if they don't work for you, sell on Cloudy Nights classifieds and buy something different.

Brian

#4 TexasRed

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Posted 10 May 2013 - 06:28 PM

Don't forget the Orion "g" series Dobs with GoTo and automatic tracking. Setup is quick and easy. They don't need to be leveled or polar-aligned, and they can be used manually without power. They can even be moved manually without losing alignment or tracking ability.

#5 GeneT

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Posted 10 May 2013 - 06:29 PM

I bought two NexStar8's for two sets of grandchildren. They are great telescopes. You can park there for a long time before having to worry about going bigger. Even if you go bigger, you can keep it for a grab and go, or for situations where less is more.

#6 kenrenard

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Posted 10 May 2013 - 08:20 PM

I've never personally viewed through the 8 but a club member has the 6 and I was pretty impressed with what I saw in it. The 8 could only be better in terms of aperture. The gentleman in our club uses a power tank and also does some astro photos (short exposure). I've seen a number of Messier objects and they look pretty good.

As Paco says it will take some time to cool. As texasred says the xt8g is another option if you want to get some wider views and also play manual.

That way if the tank runs out you can still view manual.

Good luck with your decision.


Ken

#7 mfromb

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Posted 10 May 2013 - 10:24 PM

SCTs have a longer focal length (1500MM or 2000MM, depending on 6" or 8") compared to a Dob (most end up at 1200mm). So the SCT is better for high power (planetary) and the Dob is better for low power, wide views (star clusters).


I don't mean to nit pick, but I want to sanity check what my current understanding is. Is this a true statement?

It would seem to me that the only assured 'advantage' of the longer focal length isn't necessarily 'better' high power views, but that you can obtain a higher power using any given eyepiece, or the same power while using a longer focal length eyepiece?

I'm not sure this classifies as being literally 'better' for higher powered views and, if they were actually better, that this could be attributed to the longer focal length?

:question:

#8 star drop

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Posted 10 May 2013 - 10:50 PM

It would seem to me that the only assured 'advantage' of the longer focal length isn't necessarily 'better' high power views, but that you can obtain a higher power using any given eyepiece, or the same power while using a longer focal length eyepiece?

Correct.

#9 kfiscus

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Posted 10 May 2013 - 11:21 PM

I'm a dob lover but got to use my friend's new 6SE over the fall and winter. I too powered it with my power tank. The views are high quality. It is VERY user friendly. (I tried and succeeded to learn it without reading any instructions.) The mount is well engineered. The tracking is very good. I put it on the Ring Nebula, put the dust cap on, and came back out an hour later. The Ring was still in the view.

#10 AstroTatDad

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Posted 11 May 2013 - 02:34 AM

I have owned the 6SE for 2 months now, really great scope. With these scopes you don't need high priced eyepieces, low to mid range EP's are good. The 25mm that comes with it is pretty nice. PowerTank is a must, using AA battery's will die fast and when they start losing power the scope will start losing alignment and slew around the block LOL. The tripod that come's with the 6-8SE is pretty good, I don't put the legs extended all the way out on mine to help reduce vibration. I also picked up the vibrations pads, helped out a lot. Right now you can pick up the 6 and 8SE 10% off normal price until June.

#11 Mentor

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Posted 11 May 2013 - 07:30 AM

SCTs have a longer focal length (1500MM or 2000MM, depending on 6" or 8") compared to a Dob (most end up at 1200mm). So the SCT is better for high power (planetary) and the Dob is better for low power, wide views (star clusters).


I don't mean to nit pick, but I want to sanity check what my current understanding is. Is this a true statement?

It would seem to me that the only assured 'advantage' of the longer focal length isn't necessarily 'better' high power views, but that you can obtain a higher power using any given eyepiece, or the same power while using a longer focal length eyepiece?

I'm not sure this classifies as being literally 'better' for higher powered views and, if they were actually better, that this could be attributed to the longer focal length?

:question:


A telescope with a longer FL will allow you to obtain a higher magnification using eyepieces with longer focal lengths. These longer FL eyepieces are generally easier / more comfortable to use. This can be overcome somewhat through the use of modern (and very expensive!) eyepiece designs, or through the use of a barlow (which introduces more glass to the optical train). I would say this is still an advantage for the telescope with the longer focal length. The shallow angle of the optical cone in the longer FL scope (assuming a constant aperture here) will also be more forgiving on eyepieces as well. A scope with a very fast focal ratio will ask more of the eyepiece.

Conversely, a shorter focal length will allow you access to wider fields of view than a longer FL scope. I moved from a 7" Mak (FL 2670 mm) to a 4" refractor (FL 880mm) and would never go back. The TFOV in the Mak felt like looking through a straw compared to the refractor. I love being able to use my 35mm Pan EP to turn my scope into a 102mm finderscope! To illustrate my first point, I now need an eyepiece with a FL of about 4mm to max out the magnification on my scope, while in the Mak the high-power EP was closer to 10 mm, even with the much greater aperture. If the apertures were the same this difference would have been even greater. Would you rather look through a 10mm plossl or a 4mm plossl?

#12 MikeBOKC

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Posted 11 May 2013 - 08:07 AM

When people ask me about a first scope, unless they have very specific needs that would point in an equally specific direction, I tell them that IMO the best value on the market for a combination of aperture, versatility, user friendliness and portability is the 8SE. There's a reason Celestron has sold a ton of these scopes in their various models and configurations for many years now They just work, for a quite reasonable investment.

#13 Tony Flanders

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Posted 11 May 2013 - 08:12 AM

SCTs have a longer focal length (1500MM or 2000MM, depending on 6" or 8") compared to a Dob (most end up at 1200mm). So the SCT is better for high power (planetary) and the Dob is better for low power, wide views (star clusters).


I don't mean to nit pick, but I want to sanity check what my current understanding is. Is this a true statement?


I would say that it's true, but not for the reasons stated.

It is true that the shorter focal length of a Dob gives it a clear advantage for wide-field views. This can to some extent be offset by using a reducer/corrector on an SCT together with 2-inch eyepieces. But even then, a normal Dob has a clear advantage in this department.

As for high power, the longer focal length of an SCT isn't really an advantage. It is very easy to increase the effective focal length of a Dob with a Barlow lens. You can get a very nice Barlow for $100 -- not an expensive accessory at all.

However, the motor tracking of an SCT is indisputably an advantage at high power. Sure, Dob owners (including me) will say "Oh, it's not so bad" or "It's easy to learn to hand-track at high power," both of which are true -- in a way. But the best hand tracking in the world is no substitute for having your target just sit there in the middle of the field of view. Even when you take a break, or fiddle around in your case for that other eyepiece or filter, or simply zone out.

#14 Pharquart

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Posted 11 May 2013 - 08:51 AM

It would seem to me that the only assured 'advantage' of the longer focal length isn't necessarily 'better' high power views, but that you can obtain a higher power using any given eyepiece, or the same power while using a longer focal length eyepiece?


I probably didn't express myself as well as I should. (And I take no offense at all to your clarification.) I was trying to say that, in general, if you want high magnification views, you're better off starting with a long focal length because, as you and others have pointed out, longer (cheaper, more comfortable) focal length eyepieces will get you there. You can always jack up the magnification on a short focal length instrument, but if you're trying to get to 350x, you probably don't want to start with a 80mm F/5 scope. (And yes, I know I'm exaggerating. Please don't have all the short tube 80 guys pile on convincing me of all the great views they can get with their scopes!) On the other hand, if you generally like wide field, low power views, starting with a C11 (F/10, 2800mm focal length) takes a lot of correction to get you there.

In truth, the difference between 1200mm and 2000mm in focal length isn't that great. Want to get to 300x? 6.6mm vs. 4mm (or corresponding Barlowed eyepiece) isn't that different. You're still going to want something with better eye relief than a Plossl.

I totally agree with Tony: tracking at high powers is worth a bunch. Objects pass through the field of view very quickly at high powers. And one you lose them, you have to go back out to lower powers to find them again. At least I do.

Brian

#15 wirenut

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Posted 11 May 2013 - 09:40 AM

tracking at hi powers is worth a lot, so much I made a EQ platform so I'd have tracking. it's another thing to be able to use high power when things don't allow it. one thing that won't allow it is a scope that isn't at ambient temperature. Here the reflector/dob's has the advantage. it's open tube allows it to reach ambient temps much faster so you can use it sooner. this of course depends on where/how you store it. if you store scope in a unheated garage or shed where temps are close to that of the outdoors it's not a issue but if you store it in home it can be.

#16 YetAnotherHobby

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Posted 11 May 2013 - 09:54 AM

My first telescope was a Nexstar 8". It allowed an impatient guy who wanted to see what was up there to see galaxies, nebula, and planets the first night out. Eventually aperture fever and a desire to know more about astronomy led me to a dob and the art of star hopping, but in my back yard light pollution I still prefer the convenience of goto (that impatience thing again). You can't go wrong with an 8SE for the price. There are some tips and tricks to getting the most out of the mount - the tips don't cost a dime but make a big difference in performance. Have a look at www.nexstarsite.com for lots of great info.

#17 Jon Isaacs

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Posted 11 May 2013 - 10:24 AM

Regarding focal length and magnification...

First and foremost, getting good views at high magnifications requires a stable atmosphere, that is excellent seeing. To paraphrase Rod Mollise, "When it comes to planetary viewing, seeing is not the most important thing, it's the only thing."

Getting good views at high magnifications is about getting the image to the focal plane, that means good optics, a scope that has cooled down and stabilized, a scope with enough aperture to push the limits of the seeing.

Cool down, the necessity for the optics to be with a degree or so of the ambient air, is critical because a warm scope results in tube currents and changes in the optics which disturb the view. Thermal equilibrium is a moving target because the temperature drops as the night progresses. In general, Newtonians/Dobs have an advantage in reaching and maintaining thermal equilibrium because they can actively cooled with a fan while observing.

There are other small advantages to a Newtonian, the smaller central obstruction results is some what better planetary contrast.

Notice no mention has been made of the focal length or focal ratio...

In terms of a mount, a solid, stable mount that does not vibrate when you touch it is number one. A stable mount allows the observer to focus in real time instead of having to wait for the scope to settle after each tweak. Tracking is nice but not at the expense of optics or thermal equilibrium or mechanical stability.

So... I prefer Newtonians for planetary viewing, I find there is a small but real advantage. But in the big picture, either the 8 inch SCT or the 8 inch Dob is plenty capable of providing very good planetary views. It is, after all, about having your scope ready to take advantage of those nights when the seeing is excellent and both can do that.

Jon Isaacs

#18 js1976

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Posted 14 May 2013 - 10:51 AM

Ok, sounds like I can't go wrong with either choice. A 10 inch Zhumell or a Nexstar 8. The Celestron is certainly a much larger investment, but I might be able to keep my kids interested longer since I won't be spending as much time searching the skies.

#19 jerwin

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Posted 14 May 2013 - 11:09 AM

the tracking you get with a goto scope like a nexstar is very nice when sharing the eyepiece. With a Dob, if you have something in the eyepiece and want to let someone else see it, you often need to place the object almost off the eyepiece, so by the time they look it's drifting towards the center. Depending on how long they look, you might need to fine it again, or reposition it for the next kid.

For me, the goto is nice, but the tracking is why the scope costs more.

Having said that, there are kits you can put in a dob to get them to track.

A dob takes long to cool off if you leave it in your house, but even with that cool off time, I'm almost always able to view the night sky faster with my dob than with my goto scope.

If I could only have 1, I'd pick my goto scope, but that would be like picking which kid you love the most.


Good luck and clear skies,
Jim

#20 csrlice12

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Posted 14 May 2013 - 11:20 AM


It would seem to me that the only assured 'advantage' of the longer focal length isn't necessarily 'better' high power views, but that you can obtain a higher power using any given eyepiece, or the same power while using a longer focal length eyepiece?

Correct.


However, that higher power comes at the cost of a narrower FOV.....

#21 stratocaster

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Posted 14 May 2013 - 11:33 AM

I have a 10" dob and love it. Occasionally I will struggle trying to find a faint object. Some friends with push-to dobs just hone right in on them and I'm still putzing around. This is a two-sword in my view, though. When you've got to find something you tend to learn the sky better. With push-to or go-to, there is really no need to learn. I also find "the hunt" part of the enjoyment of the hobby...to a point. I've actually looked at some after-market push-to equipment for my dob, but it's a bit expensive.

Having said that, I've seen fellow club members say they could never find anything before they got a push-to. Now they say they spend more time viewing and less time searching.

To the OP, you mention you may be able to engage your kids more because you will spend less time searching. So it sounds like the go-to feature (or perhaps a push-to feature on a dob) is where your primary value is.

#22 pftarch

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Posted 14 May 2013 - 04:16 PM

As far as push to/goto to find things, I'll leave that up to you. (There are times I wish I had push to on my Z10, but those times are rare). I love the simplicity of not relying on electronics and not having to align/set up one more thing.

As far as tracking, I may be in the minority here, but smooth dob motion makes up for tracking 99% of the time in my opinion. I have an EQ platform that I used to use most of the time with my old (spring bearing like the Orion XT) Z10. On the old dob, powers much over about 100X were difficult to hand track. With my new(er) Z10 with the friction bearings, hand tracking at 300X is not a big deal due to the smooth motion. Typically I don't even bother with the platform because it's one more thing to carry out, set up, and fuss with. (In addition, I have a cheap platform that introduces a fair amount of additional vibration to the setup.) With what my usually miserable NH skies allow for magnification, the platform really isn't necessary. (I also have an SVP GEM, but the biggest scope that I own that it will handle is a 5" MAK, and the views through my Z10 are much better. The SVP tracks fine, but I LOVE my dob.)

I've never looked through an 8" SCT, so I can't compare it to my 10" reflector, but, the 10" gives you over 50% more light gathering ability due to aperture alone, (and the CO is smaller) and, with the SCT and a mirror diagonal you are going through one piece of glass and 3 mirrors before you hit the eyepiece vs two mirrors with a reflector. My guess is that the 10" will offer up quite a bit more, but I need someone who owns both to confirm that. (I know my Z10 is a HUGE jump over my 5"MAK or 80mm refractors.) If possible I would recommend the 8" over the 6" if you are going the SCT route.

The 8" SCT offers advantages of size, tracking, and GOTO. The dob offers the advantages of light gathering, simplicity, and much less cost.

Either way you win. For ME, I would go with the dob, but that is an EXTREMELY subjective personal decision. I usually recommend the DOB to people starting out, but that is largely because they want to stay under $500. If you have that limit, the dob beats most other scopes hands down. If your budget is more flexible, then it becomes more of a horse race.

#23 Kevdog

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Posted 14 May 2013 - 04:17 PM

Ok, sounds like I can't go wrong with either choice. A 10 inch Zhumell or a Nexstar 8. The Celestron is certainly a much larger investment, but I might be able to keep my kids interested longer since I won't be spending as much time searching the skies.


If you have kids in the equation, then there is no doubt in my mind.... get the 8SE. I had (briefly) an XT12i. I'd get a good view of Saturn in the eyepiece and then it was like mission impossible with both my wife and son.... "You have 20 seconds to view Saturn... go go go!!!!!". The tracking is the thing you will want. The goto is also great for finding lots of stuff quickly. Even though my son is interested in the stars and planets, being 6 his mind wanders quickly!

My Meade LT8 was much better for us, even though I gave up a lot of aperture. Now I have a C11, which blends both. Of course the money is a lot more but IMO it is worth it.

#24 geekgroupie

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Posted 14 May 2013 - 07:26 PM

When people ask me about a first scope, unless they have very specific needs that would point in an equally specific direction, I tell them that IMO the best value on the market for a combination of aperture, versatility, user friendliness and portability is the 8SE. There's a reason Celestron has sold a ton of these scopes in their various models and configurations for many years now They just work, for a quite reasonable investment.


It's what was picked out for me when I pinned an astrophysicist down and said, "if you were going to give a scope as a gift, what would you choose". It was the only way I could get a straight answer out of him, hee hee

#25 pjensen

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Posted 14 May 2013 - 10:49 PM

Having said that, I've seen fellow club members say they could never find anything before they got a push-to. Now they say they spend more time viewing and less time searching.

To the OP, you mention you may be able to engage your kids more because you will spend less time searching. So it sounds like the go-to feature (or perhaps a push-to feature on a dob) is where your primary value is.


Just to add on here - for a newbie to find something can be an exercise in frustration. Even if the telescope is dead on an object, a newbie may not even see it. Getting the scope to the right place is difficult (at first) - craning your head to look through a finder scope, trying to figure which star is which (with light pollution) and then moving the telescope in the right direction. To add in complexity, once the object is found - it won't stay in the eyepiece for long.

The goto not only solves all these issues (finding and tracking) - it helps with the object identification. Just press the info button, and then page down for all the details.

It also trains a newbie what objects look like. Many times I have not been able to see the object at first, but I know it's there (if all the gotos are dead on with nearby stars). So I put a sweat shirt over my head and eyepiece, close my eyes for a couple of seconds - then open them. There it is. I can track that object for 30 minutes, and try to make it show up better (changing eyepieces, moving the object off center).

What's really cool is to sequence through dozens of objects - and come back to the ones that were no-shows earlier. Many times an object will be visible later on.

All I can say is I'll never go back to a non-goto. To observe so effortlessly is simply amazing - and with no neck muscle aches afterwards! :)






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