SCT versus Dob (was David Hinds Great Service)

[leehawkins]

Total newbie here,

why is it the scope (CPC 1100 GPS XLT) that Trever got , only a 3rd of the size of a dobsonian sky-watcher 300P, what sets them apart, power, technology, what is it , price wise, what are you gaining and what are you losing, but spending more cash for, paying for, elaborate mounts, Each time more technology comes in on the Mount's/tripods are you diminishing actual seeing power of the scope, to keep in the same price range?

You mount a sky-watcher 300P on a nice technologically advanced mount, the price double/treble, is this the case, what are you paying the price for ?

You got lots of configurations of telescope, but what can you see more out of when you plonk it on the ground and point it to the night sky

Very confusing i recon :? a short ass CPC 1100 GPS XLT or a giant Sky-watcher 300p what one would give the best view

[Kaptain Klevtsov]

The Dob. is a large aperture small technology 'scope, the CPC1100 is a large aperture big technology 'scope.

The main difference is, you take both outside, plonk them down and look through them. One shows you random stars, the other shows you what you want to look at. The Dob. then allows all the stuff you are looking at to drift away, so when you go get your wife to see Saturn, its disppeared by the time she looks through the 'scope. The CPC will track things, making life easy.

Kaptain Klevtsov

[SteveL]

(Message thread split to keep the David Hinds thread on topic)

[Milamber]

The Dob. is a large aperture small technology 'scope, the CPC1100 is a large aperture big technology 'scope.

The main difference is, you take both outside, plonk them down and look through them. One shows you random stars, the other shows you what you want to look at. The Dob. then allows all the stuff you are looking at to drift away, so when you go get your wife to see Saturn, its disppeared by the time she looks through the 'scope. The CPC will track things, making life easy.

Kaptain Klevtsov

Ahem ... ahem, ahem :nono: *Most* dobs...

Arthur

[SteveL]

LOL! when i split the topic I wondered how long it would be before you noticed this

[Kaptain Klevtsov]

I was specifically answering the question relating to the SkyWatcher 300P. Good point though, and you could add a motorised platform to the 300P.

Pedantically, when does the Dobsonian mount become an Alt. Az. motorised mount, and is the addition of motors enough to make it no longer a Dobsonian? I suspect that "Deep Blue", or whatever its called now, would be even more expensive than the CPC11 Arthur , so the comparison wouldn't work anyway.

Kaptain Klevtsov

[Milamber]

Well, it's still a Dobsonian-mounted telescope - and it has goto and tracking as well. Anyway, you talked about the dob and the cpc...

So there

[dogfish]

why is it the scope (CPC 1100 GPS XLT) that Trever got , only a 3rd of the size of a dobsonian sky-watcher 300P,

One of the reasons the CPC is more expensive might be because it is more portable. SCT's fold the light path all the way back down the telescope tube so that the cone of light emerges at the back of the telescope. This means that despite it being much shorter, it actually has a longer focal length than the Dob. I'm presuming it's more expensive to make SCT's than it is to make the simpler Newtonian tubes as even as an OTA (leaving aside all the fancy mounts and stuff) SCT's are more expensive to buy than are Newt's. Like the others have said, it's also more expensive because of the computer wizardry, motors, and GPS satellite technology.

Cheers, Martin

[leehawkins]

The Dob. is a large aperture small technology 'scope, the CPC1100 is a large aperture big technology 'scope

But the the bit i struggle with, is the CPC 1100 and lots of other brands/make/models same design , put up against a dob 300P in size, no technology or hardly eny on the dob, the cpc1100 with lots of tech stuff on it, but half the size, but costing an arm & a leg, how i would see it, you should only have half the actual seeing power on the cpc1100, the big part is the tech stuff on it,

sort of finding it hard to get over what i mean.

[GordonCopestake]

The reason the Dob is physically larger than the SCT is because the SCT uses both lenses and mirrors to fold the light path meaning the tube can be twice as short as a dob (newt). The extra bits of glass in the SCT is one thing that makes it more expensive (you DONT need to have all the fancy GOTO and electronics with the SCT design, but most are sold this way).

Wikipedia has some nice info on both types of 'scope:

http://en.wikipedia.org/wiki/Schmidt-Cassegrain_telescope

http://en.wikipedia.org/wiki/Newtonian_telescope

[Kaptain Klevtsov]

The "what you can see" bit relates almost entirely to the aperture. The Dob. is 300mm, or 12", the SCT is 11", so the Dob. would let you see slightly more due to the larger aperture. As to actually finding stuff, that's where the wizardry comes in.

Kaptain Klevtsov

[barkis]

I perceive the Dobsonian, and let's not forget why it is called that, to be the very basic wooden contraption, that serves very well to support the optical configuration we all know as the Newtonian. I also think it's time that the term Dobsonian ceased to be applied to instruments that are far too sophisticated in their design which is far removed from the Initial Dobsonian concept.

The man built the support for the mirrors that way, in order that the not so well off would have a chance at an economic telescope.

Dobson will be more than delighted that his name is synonymous with sidewalk astronomy, that is what he intended. I think he would baulk that his name is also given to some of the sophisticated light buckets, that are computer enhanced , technological marvels that are commonplace now.

Ron.

[Milamber]

Likely true Ron - but things evolve and move on... I doubt if Logi-Baird would approve of hdtv but still...

The original point though is well answered in your last post. Dobsonian mounts are by definition the cheapest way to get a couple of bits of mirror pointing in the right direction to see the stars. Anything else is just window dressing and adds to the cost - hence why EQ or fork mounts are expensive.

Arthur

[Adam Hinds2]

Total newbie here,

why is it the scope (CPC 1100 GPS XLT) that Trever got , only a 3rd of the size of a dobsonian sky-watcher 300P, what sets them apart, power, technology, what is it , price wise, what are you gaining and what are you losing, but spending more cash for, paying for, elaborate mounts, Each time more technology comes in on the Mount's/tripods are you diminishing actual seeing power of the scope, to keep in the same price range?

You mount a sky-watcher 300P on a nice technologically advanced mount, the price double/treble, is this the case, what are you paying the price for ?

You got lots of configurations of telescope, but what can you see more out of when you plonk it on the ground and point it to the night sky

Very confusing i recon :? a short *beep* CPC 1100 GPS XLT or a giant Sky-watcher 300p what one would give the best view

Erm, its not a 3rd the size the CPC is 280mm or 11" and the dob is 300mm or 12" so there's not much in it. The CPC is packed with technology whereas the dob is a simple nudge to design. the XLT coatings will make up for a little, but not all, of the smaller aperture.

All the CPC's are available on a special offer at the moment from most UK dealers.

[leehawkins]

Put a ruler on them, measure end to end, i think you'll find one of them is alot longer!

[GordonCopestake]

Adam is talking about the aperture, which is the most important figure

[Adam Hinds2]

Put a ruler on them, measure end to end, i think you'll find one of them is alot longer!

usually, but not always, when the size of a telescope is quoted it is the aperture (diameter of the optics) that is being referred to not the focal length.

Although as standard the length of the CPC is 1/3 or close to 1/3 of the dob, it is actually nearly 2X the focal length optically, so the CPC will give nearly 2x the magnification and nearly 0.5 the field of view. HTH.

[Kai]

If i could i would have both of these scopes as they are as different as chalk and cheese but both give fantastic views,Its just that they excel in different areas.

I have looked through both scopes and i have to say that M13 in the Celestron is unforgettable where as M51 in the 300p is spectacular.

Horses for courses i re con

[GordonCopestake]

My ideal 'scope is a 16" f/2 SCT with no aberation, no central obstruction and a few barlows

[supernova]

I would like to add my bit if I may. The reason I have chosen a dob is because if I am going to buy a scope for say £2500 I would like the biggest apeture! so for that price I can have top optics with no frills, electronics can fail and so can motors, I dont knock goto its excellent, but not for me, after all a scope is for looking through innit, add ons can come later but for now I will have to use my sky map.

The only problem I can see coming up for me is humping the thing outside every clear night

Just one more thing my wife aint intrested so I can follow my chosen object and I can keep it all to myself

This is just my opinion. hope you dont mind

[Andrew*]

after all a scope is for looking through innit

AND imaging through! But you're right - if I wouldn't be into imaging I would have gone down the dob route. Dobs are for observers. EQs are for imagers. That's how I see it anyway...

[Milamber]

Dobs are for observers. EQs are for imagers.

How does it go? "We few, we happy few, we band of brothers..."

Arthur

[leehawkins]

usually, but not always, when the size of a telescope is quoted it is the aperture (diameter of the optics) that is being referred to not the focal length.

Although as standard the length of the CPC is 1/3 or close to 1/3 of the dob, it is actually nearly 2X the focal length optically, so the CPC will give nearly 2x the magnification and nearly 0.5 the field of view. HTH.

If this is right what Adam has stated, to me there should be no need for a 12'' dob to be so large, or for that matter any telescope, that is measuring buy size/bulk, not aperture/mirror size.

[themos]

Shorter focal lengths make for shorter telescopes in the same design class.

The Dobsonian is in a different design class than the CPC.

Shorter Dobsonians are possible but the downside is the expense of making a good short-focal-length mirror in 12" aperture. They will have to look like umbrellas instead of almost flat pieces of glass.

[leehawkins]

Although as standard the length of the CPC is 1/3 or close to 1/3 of the dob, it is actually nearly 2X the focal length optically, so the CPC will give nearly 2x the magnification and nearly 0.5 the field of view. HTH. usually,

The CPC 1100 GPS XLT could be stripped of all the technology, to leave a scope of half/3rd of the size of 300P dob, but with twice the focal length & twice the magnification over the 300P.

That's if i am understanding this properly