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Light Pollution... Should I upgrade?


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Hey,

I live in an area with pretty bad light pollution.

I currently have a 5" reflector (Celestron Astromaster 130EQ) and the views of DSOs are pretty poor (I have a light pollution filter, but it didn't make any difference).

If I were to upgrade to, say, an 8" reflector, would this make much difference?

It's obviously quite a lot of money, so I don't want to waste it on a lost cause.

Thanks

Matt

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In my experience it doesn't make much difference. I was out last night cursing the orange sky. I can comfortably pick up some DSOs but others evade me despite having a goto scope. LP filters don't really make much difference.

Upgrade to a house in a darker place? Or... focus on planets. I saw Saturn in my new scope for the first time last night and ended up dancing around the garden with excitement. Brilliant!

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I wish you had not said that about LPF's as I bought the Skywatcher one and am still waiting for it to arrive :-( Not so excited about it now.

Lol I remember that feeling.

I thought it would solve all my problems, but unfortunately it didn't really have any affect.

But maybe you will have a bit more luck than me

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there's no doubt that darker skies are better but assuming you are like most and live near or in a city then it's just something you have to deal with unfortunately.

personally I have no doubt that a larger scope will improve things but manage your expectations about what you'll see of course as even with very large scopes, most galaxies are grey smudges and most nebulae small and uninspiring - it's what they are and that you can see them at all that's amazing to me.

you have a decent scope but it won't give photo quality images of galaxies etc and some will not be visible even with a larger scope from home. BUT an 8" scope will be a world apart from your current scope on most objects. you can adopt the following approaches to combat it somewhat:

  • I personally am not keen on filters other than an Oiii and a UHC which both make a big difference - even in LP they help pick things out well. Some targets respond better than others.
  • Find the target and then increase the magnification - more magnification means darker skies but don't overdo it
  • Get your eyes really dark adapted as much as you can
  • Wear something over your head like a black sheet which really helps to reduce the impact of local lights etc
  • A dew shield is really a light scatter shield in most cases - make one from a camping mat - same impact as the last point
  • Get to a darker site if poss of course
  • More aperture will often help as it equates to more focal length and more magnification with your EPs.
  • When the sky is not that transparent and there's any mist/dew in the air, light pollution is always worse - concentrate on brighter things like open clusters, double stars, moon and planets in these conditions.
  • When the skies are transparent and look dark then make the most of them concentrating on things you cannot see when the sky is worse.

the problem with aperture is that you can always get more and it's important to get the most out of the gear you have until you 'grow out of it'. with practice you'll see a lot with your current aperture and it's small enough to put in the car etc when you get a chance.

hope this rambling answer helps a bit and shows you don't really need to spend loads of cash to improve things a little.

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Once an object becomes overwhelmed by background sky-glow then it will not visible in any aperture. Galaxies suffer particularly badly as they're dim and don't respond well to light pollution filters. That said, if an object is visible then larger aperture will always show you more. So, yes, you will see more with an 8" or 10". However, going to darker skies will make even more difference.

The best thing, of course, is to take a >10" scope to dark skies. Let's put it this way: my club owns a 25" Dob in about mag 5.5 skies. When I take my 12" to ~mag 6.25 skies I get better views for most objects. The 25" gathers over 4 times as much light as my 12". Skies matter. Under the same skies, the 25" performs better. e.g. dust lanes in M31 are more salient.

Finally, light pollution filters cut out a lot of light. As a consequence, they work better with larger scopes. With smaller scopes you can only use very low magnifications with these filters (5x to 10x per inch). This is obviously frustrating since some of the objects on which they work best are planetary nebulae, and these need higher powers. They also work well on extended nebulae such as M42 and the Veil, however.

So, no, upgrading isn't a lost cause but no telescope will show its true potential unless you take it somewhere dark. My advice is first to take your current scope somewhere darker then see if you still want to upgrade.

Edited by umadog
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Thanks for the great responses guys :)

Maybe this is a bit of a stupid question... but what actually are the advantages of upgrading?

How would the view of, say, Saturn differ between a 5" and an 8" scope?

And what about something like M13?

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generally speaking more aperture gives you two benefits - more potential resolution and more light gathering. it also gives you more cost and weight of course and they take a little longer to cool - 5 minutes per inch of aperture I have heard a few times. there can apparently be issues with seeing through a larger column of air but I tend to ignore these at the apertures we tend to use as amateurs and I have never really seen this effect to my knowledge.

so Saturn will be brighter and should show more detail with the 8" as the maximum mag (I use 1.5x mm of aperture) is about 300x whereas with the 5" it's 187x approx. so the 8" scope is less 'strained' at say 180x than the 5" which is really pushing its limit then - subject to seeing etc of course. all that said, as my 6" f11 has more contrast than my 12" f5, I tend to prefer the 6" for planets which is why I bought that.

hope this helps a bit.

in terms of light gathering the 8" gives about 50 square inches of light gathering area where the 5" has around 20. eg M13 will be a lot brighter and with more stars being resolved.

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I'm going to be the opposition party here and say that i have a bog standard 1.25" SkyWatcher LPF and i can honestly say that it makes a difference in my observing.

My main scope is also a 5" reflector and with the LPF attached it really does give greater contrast and allows me to see DSO's mush easier then without the filter.

I live about 20 miles from Dublin city and a mile from from the coast. I wouldnt say the LP level where i live is BAD.............but its enough.

As for the difference between a 5" and an 8" scope................

I can only imagine the views are like chalk and cheese. LP is still a factor though.

P.S.~~M13 in my 5" scope is SPECTACULAR.

Edited by LukeSkywatcher
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Keeping it simple, larger aperture grabs more light (information/resolution of detail) and the length of the tube determines potential magnification for a given eyepiece. If you want to magnify an object using a particular eyepiece, what you are doing in fact, is stretching the light and explains why the image gets darker as the magnification goes up. If however you have more light to start with then you've got more to 'spend' when you stretch or magnify this light WITHOUT losing quite as much detail. Think of light as a vehicle that carries information. The more of it you can get hold of regarding a target, the more information (resolution) you will be able to read or see. The longer the tube the more narrow the light cone that arrives at the eyepiece which ultimately means that the eyepiece has less work to do than say with a scope that is much shorter and which will produce a wider light cone that then has to be brought to focus - and the need for better (expensive) eyepieces.

All this comes at a price, a weight and so the logistics of setting up and the time it takes is more of a consideration - especially if you are travelling to a dark site.

Hope that helps a bit!

James

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Yes, the LP filter does make a difference. A big difference, potentially. Under moderate light pollution an OIII filter makes the The Veil visible, when it would be invisible without. Under darker skies, it brings out loads of filamentary detail that wouldn't be visible otherwise. Personally, however, I find myself using my UHC filter much more with my 12" than I ever did with the 8". The image darkened too much in the 8" for my liking.

A filter isn't a bad investment even with a smaller scope, since you can always use it in future scopes. I buy only 2" filters and use a threaded 2" -> 1.25" adapter for the smaller eyepieces. Very convenient.

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Well here we are once again.. the $65,000 question. the guys here have answered this well. I in the most part right. One of the biggest issues we have is sky quality. I've used a few... err lots of scopes. And when all said and done, from the back yard the 8" Newt is near perfect for UK skies.

Large apature offers a lot, but it does increase seeing issues also. The 8" tends to cut through this nicely.. the LPR does make a slight difference in visual.. and stacks in Astrophotography.

Rob

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my understanding is that you are looking through a wider column of air so looking through more turbulence, but to be honest I have never seen the effect myself. maybe I need a bigger scope!

Edited by Moonshane
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I think that's a myth:

SkyandTelescope.com - Visual Observing - Four Infamous Telescope Myths

Two things are true, however, which could explain how the myth came to be:

1. Larger mirrors take longer to cool. I can well believe that an uncooled 12" would be beaten by a cooled 8". In addition, scopes with larger mirrors are more likely to be truss Dobs. These suffer from more thermal issues than solid tube Dob. An equatorially mounted scope is said to be better still since the mirror is further up from the ground.

For planets it may well be that an 8" is adequate on most nights. However, a bigger scope pulls more light and that has obvious advantages for DSOs. The OP was asking about DSOs and he will definitely see more detail with a larger scope and darker skies. In principle, the larger the better.

2. A larger telescope has a greater potential angular resolution. The higher this potential resolution, the more stable the atmosphere needs to be to support it. That doesn't mean the view will be worse in the larger scope. Simply means that the limiting factor is more likely to be the atmosphere than the optics. For example, one might never push a 3" scope past, say, 150x. If the atmosphere limits the views to, say, 300x on a particular night then the 3" isn't limited by seeing. A 12", on the other hand, could theoretically dish out over 500x. However, it won't be able to do that due to seeing. In this sense the larger scope is more affected by seeing.

Edited by umadog
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nice one Umadog - another myth I can forget then!

I completely agree with your points made too and they are certainly borne out by my observations although I do still feel my 6" f11 gives a much better view of planets. I'll have to do a proper assessment with someone more experience sometime soon.

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That might be because the mirror is better. It might also be because it's F11. There'll be way less coma then at F5.3 (coma depends on the square of the focal ratio) and also, of course, a proportionally smaller secondary obstruction.

The best test is stop your 12" down to 6" and see if that makes the view better. I bet it doesn't.

Edited by umadog
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my understanding is that you are looking through a wider column of air so looking through more turbulence, but to be honest I have never seen the effect myself. maybe I need a bigger scope!

Your quite right.. I have experienced this a few times and had to drop back in apature to acheive better contrast.

To be fair in the most cases your fine. I live near the coast so receive funny seeing conditions at times through the year.

Rob

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