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Nexstar 4se and 8se


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At the same magnification both will give the same size, images in the 8SE might show a bit more detail though. The 4SE has a focal length of 1325mm and the 8SE 2032mm so for any given eyepiece the 8SE will give a bit more magnification. (telescope focal length / eyepiece focal length)

http://astronomy.tools/calculators/field_of_view/

 

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Owned both and enjoyed both. 4SE has max magnitude of 240x, whilst 8SE has max magnitude of 480x. So yes you will be able to see bigger images of the planets, however just remember that in the UK at least there are not many nights were you will get steady views that would hold going above 300x normally. Also, as with the different focal lengths of each scope you will get higher magnifications in EP’s in the 8SE due to this as Cornelius says. With the larger light grasp of the 8SE you will see better images of the planets, so images will be better in the 8SE.

 

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The 8se has twice the resolving power (ability to separate detail) and the image will be 4 times brighter (at same mag).

Resolving power is dependent on diameter of the mirror or lens. Double the diameter and you double the theoretical resolution.

Brightness is dependent on surface area. Double the diameter gives you 4x the surface area for catching light.

The 8se will bring significant improvements to your planetary viewing over the 4se. Only caveat is that the tube is a little heavier than the mount would like when used at typical magnifications for planets (say over x150). There’s a lot of wobble.  For this reason some users pop the tube onto a more substantial mount for planetary and at other times use the normal 8se mount for casual goto fun.

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  • 3 weeks later...
19 minutes ago, paulhummerman said:

What causes the "wobble"? Vibrations through the ground, wind, touching the scope? If you eliminate all these, could there be other sources of wobble?

The 8SE is at the weight limit of the mount. 

So at high magnification there will be some wobble after focusing for a couple of seconds.

 

I wouldn't let that turn you off to an otherwise great scope.

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4 hours ago, paulhummerman said:

What causes the "wobble"? Vibrations through the ground, wind, touching the scope? If you eliminate all these, could there be other sources of wobble?

There is also the visual 'wobble' caused by unsteady seeing, turbulence in the atmosphere disrupting the incoming beam of light from the object. There is nothing you can do about this other than come back another night. Generally the lower the object is in the sky the more likely it is that poor seeing will affect you.

The real question about magnification is this: at what point does it stop being worth increasing the magnification? If the seeing, the mount or the optics will only yet you increase the size of the projected image while not letting you detect any more detail in it, then is it worth it? Imagine using a telescope to read a distant sign. You cannot make out the individual letters. You increase the magnification and you still cannot make out the letters. So the increase in image size has produced no new information.

This is exactly what happens in planetary observation.

Olly

Edited by ollypenrice
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I've had both, the comments above are spot on but I would add the viewing experience is much better with the 8SE particularly with a low mag (30mm+) 2 inch eyepiece 

The wobble is quite noticeable when focusing and if it's windy, the goto mount is OK but really needs something more substantial if I'm honest, it's on my shopping list anyway.

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The C8 SE is one of the cheapest 8" SCT GoTo packages you can buy, and despite the price of over £1200 is entry level for this class of instrument. It is also intended as portable - you can pick up the whole package and carry it through a standard doorway. 

The CPC800 variant with the same optical tube is rock steady by comparison - and a lot heavier and more expensive.

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I moved my 8SE to a Celestron CG5 mount. A big difference and no issues with needing to worry about banging the diagonal on the original SE mount. As to the original mount, I always used vibration suppression pads, they help particularly on hard surfaces. I only changed from the 8SE because I started wanting to image and the focal length is too long for deepsky imaging.

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