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Hello from Germany + your input for a scope


uhb1966

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Hi everybody!

After tinkering about with two bad made entry level scopes from Meade, i am now considering starting this hobby in earnest, despite the often cloudy skies..

I am planning to get a allrounder telescope- a celestron 8'' Nexstar SE . I am planning to do mostly DSO imaging via an (unmodified) Canon EOS 550D directly connected to a laptop (liveview). I have already some experinece with processing and stacking the pictures taken, using my stock objectives for the camera. I think that the scop is a good allrounder and has a decent aperture while still being portable. I am planning to do most of the scoping from my backyard with occasional trips to a nearby dark place with decent elevation.

Your opinion on the scope / setup?

Regars, U.

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Hi and welcome to SGL - You say that you want to do DSO imaging, the mount of the 8SE is really not suitable for this. The mount with this scope is not a German Equitorial mount which means that you will not be able to achieve the long exposures that you will need for DSO imaging.

If DSO imaging is where you think your interest will lie, then get hold of a copy of 'Making Every Photon Count' available from the book section of the FLO website. Don't spend a penny until you've read this and understood what you need and why you need it. 

I hope that helps.

Look forward to seeing you around :smiley:

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Hello Dear swag 72,

I think he mount is not an issue as every single exposure will be releatively short, the picture i shared was even taken from a non-tracking, stationary mount. The trick i used so far was to keep every sinlge exposure below 15 seconds and than "stacking" several hundred photos. This does take an awful lot of computing time, but it helps tremendously against noise and suboptimal tracking. If i use a software that can adjust the angles of the pics, even the non-EQ mount is not an issue  ;)

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I would second Sara's advice, an 8" SCT really isnt suitable for DSLR imaging with short subs - especially with an unmodded camera. Too much focal length, and too high a focal ratio (f9)... its what some would call a "dark" telescope since the light has been diluted so much.

Use this calculation (it will be your most used) to compare the photographic speed of systems:

eg: the difference between f5 and f9:

9/5 = 1.8^2 (sqrt) = 3.24

Meaning f5 is 3.24 times faster, or to look at it another way - the data collected in one 15min sub from a C8 would take just 5min to collect with an f5 newtonian. The numbers get even more crazy the lower you go - f4 would be 5.06x faster than f9 :D

There is no room for skimping on the mount either (as already suggested), if youre getting into AP you might as well settle the job with one stroke with an NEQ6 and never upgrade again (you wont need to!).

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What would you think of the NEQ-5 Pro Goto mount? Its total weight is already 17kg...

Maybe combined with an TS Optics 254/1016 F4  Newtonian? I understand that moving from f10 to f4 would make the scope much faster?

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What would you think of the NEQ-5 Pro Goto mount? Its total weight is already 17kg...

Maybe combined with an TS Optics 254/1016 F4  Newtonian? I understand that moving from f10 to f4 would make the scope much faster?

Unfortunately that is too large a scope on too small a mount. For DSO imaging, forget about the size if the telescope, it isn't really important except as a side effect. The focal ratio (speed) is important, you want the fastest you can up to the mechanical limit of the equipment. Then focal length, as this sets the area of sky you will image. Bigger is not better, it is only different and definitely more difficult!

The standard kit recommendation for your budget is the Skywatcher ED80 plus flatner/reducer and an HEQ5 Pro Synscan mount. Ideally with an autoguider to get good long exposures.

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 Bigger is not better, it is only different and definitely more difficult!

Exactly! :)

Thats the thing that caught me out when I first started. I wrongly thought that to get a better photo, the image scale had to be larger (and fill the frame). It took me a while to realise that to make an object "appear" larger is to just crop the image to pixel scale.

Two figures you need to look into when choosing a camera or telescope is the resolution and the f-ratio - the former is measured in arcseconds per pixel. You can image anywhere between 1.0 and 3.5" p/p and get pretty good results (lower is better - especially for galaxies). To figure out the resolution and f ratio for any given combination of telescopes or camaeras - use this tool:

http://www.12dstring.me.uk/fov.htm

As for f-ratio, if you are using a DSLR then you need a fast(ish) telescope to get anywhere quickly. F5 is a good place to start, but its a speed thats only cheaply available to newtonian telescopes - to get the same speed from a refractor will cost an awful lot more money. But as soon as you go below f5, things start to get difficult (and/or expensive)

So for your budget your looking at something like a 150mm f5 newt on a HEQ5 mount - with your 550d it gives a more than healthy resolution of 1.18" p/p. But thats a big chip youve got in that camera - so to make any proper use of it you will need to factor in a coma corrector to the overall cost.

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Ok , Thanks a lot everybody!

Does anybody have experience with the "Celestron N 200/1000 advanced VX AS-VX 8" GoTo telescope"?

Not sure on the mount (its a bit new), but if you use the FOV calculator I posted the link to - you might find that with a 200mm scope youre below the 1" p/p level with your camera, which is usually the limit depending on the quality of the sky where you are.... not unless you are planning on imaging on top of a mountain somewhere, or sending it into space :D 

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Dear Uranium,

my house is on approx 1800 feet elevation, and my outpost (2miles distance) on 2700 feet elevation ;) there is some light pollution, but not too much.

Thanks A LOT everybody!

I will retreat now into my thinkers corner and start pondering ..... :/ Hopefully something meaningful will emerge ...

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I will retreat now into my thinkers corner and start pondering ..... :/ Hopefully something meaningful will emerge ...

Ahhh, we all have one of those (ie: a man cave...lol)

The key thing is to do your research first, tinker with the FOV calculators, have a look around in the imaging sub forums and make a note of what most people use (ie: anything not a Takahashi). And if you get stuck, dont be afraid to put a question out there. Remember - mistakes are expensive but questions are free  ;)

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A good starting point is an HEQ5 and an 80ED, such as this http://www.firstlightoptics.com/pro-series/skywatcher-evostar-80ed-pro-heq5-pro.html 

This sort of setup is the basis for many peoples set up and the 80ED is a good performer for the price. Strange as it may seem, you want a wider fov for DSO imaging, stuff tends to be pretty big!

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