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Imaging with an 8 inch newtonian.


oldfruit
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I do realise that i would probably be better off with a small refractor for imaging, plus a better mount but i am quite attatched to my Helios newt and was just wondering?


 


What would i need to acheive better results with the set up that i have? A skywatcher coma corrector? Or does it get more expensive than this in which case i would consider a small ed refractor.


 


Just to be clear, i am after nice results, not perfect results.


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Hi Mark


I also have the 200 Helios Newt.


What issues are you having with yours that are causing concerns.


I ask as I do not have any probs with mine.


Like you I only want to get photos I am happy with.


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Hi Mark

I also have the 200 Helios Newt.

What issues are you having with yours that are causing concerns.

I ask as I do not have any probs with mine.

Like you I only want to get photos I am happy with.

It is just the stars toward the edges of the image Graham.They do show obvious coma and I would like to improve those but do not want to spend an arm and a leg to do so.

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It is just the stars toward the edges of the image Graham.They do show obvious coma and I would like to improve those but do not want to spend an arm and a leg to do so.

 

Oh I get that as well Mark.

Simple answer and the cheapest I have found is to use the crop function in photo shop ;):lol:

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Just make sure you keep the collimation as good as possible, that will help to a degree. Then as Graham says, use the crop function, failing that you can use photoshop to get rid of the star shape error.


 



 


I've used it and it works quite well.


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The problem is Mark you could end up spending a small fortune trying to correct it.


So instead you buy a small frac, then you end up spending a small fortune on field flatteners /reducers CA correctors and the list goes on.


Either way I figure we are on a hiding to nothing. :lol: :lol: :lol:


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Crop all the way, at the end of the day most subjects come up quite small with the 200p and Canon combo so cropping the edges doesn't really effect the subject.


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I crop virtually all my images as part of my processing routine. I find it helps get rid of the most mis-snapped stars, centres your subject and also gets rid of any overlapping borders from the stacking process.

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Question. Why are small refractors better for imaging?

 

From what I have gleened so far :-

 

wider field of view.

no obstructions to create star spikes.

ED frac has better optics than a newt.

less weight so better for guiding.

 

I dare say there are better reasons but you will have to wait for some one better than me to advise.

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From what I have gleened so far :-

 

wider field of view.

no obstructions to create star spikes.

ED frac has better optics than a newt.

less weight so better for guiding.

 

I dare say there are better reasons but you will have to wait for some one better than me to advise.

Short focal length = less critical guiding

Less weight = easier on the mount

 

I like the spikes produced by a Newt

Resolution increases with aperture which is where a Newt wins

I don't think a refractor has better optics, a good finished mirror with good coatings is better

Top astrographs are RC's 

 

At the end of the day its personal choice....

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From what I have gleened so far :-

 

 

ED frac has better optics than a newt.

.

Sharp intake of breath :D

 

Im afraid "ED" optics arent necessarily better than a Newt.

An 8" reflector with good figuring and excellent relectivity, properly collimated at the right temperature and in the right atmospheric conditions will blow all but the very pricey Apo refractors out of the water. BUT getting the right conditions and everything else is not an easy thing to do thats why refractors are more predictable, (mostly :D )

Another BUT, a refractor (apo or not) doesnt have a central obstruction therefore will tend to give more contrasty images size for size than a newt. Example, take a look side by side at Jupiter through my 8" Newt then through my 4" F15 achro, far more contrast in the 4". Thats just physics

 

My 5" refractor is approx the same weight as my 8" F6 newt so beware about refractors weighing less than reflectors. The modern trend for CNC machined tubes and everything else means you need muscles like Hercules to lift some of the modern refractors. Ok a small ZS66 will weigh less than an 8" newt but an 8" refractor wont :)

 

A small Apo, say F6 will give a wider field of view compared to a longer fl newt but unless you spend a heck of alot on the scope then you will still need a reducer / field flattener if you going to put a large chip camera on it (say DSLR). I have a WO Flourite Triplet 80mm Apo with stunning optics but its still needs a flattener to flatten stars at the edge of field with my 1000d

 

Short fl does indeed make less critical guiding and they are faster so suck the photons in quicker therefore shorter exposure times but thats the case with any scope be it refractor or reflector

 

BUT, theres always a but, it all depends on what you want to image. If you want swathes of nebula over several degrees of sky then you really need a short focal length scope (or very very big chip camera and short FL scope, F2) but if your after detail in a galaxy or planet then perhaps a coma corrector for your scope would be the cheapest option.

 

Sorry about the ramble but its a big topic and theres alot of variables in this lark :D

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