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Views on aperture for combatting light pollution


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Hi folks

I have fairly bad light pollution to the South (Bortle 7 or 8 I would guess) and struggle to see anything other than the brightest DSOs with my Skywatcher Skymax 127 (I know that's not an ideal scope for DSOs) which I've had for several years.  I would just like to be able to see more of the Messier catalogue (to start with). 

Would a bigger aperture help with visual observation of DSOs? I was thinking of an 8 or 10 inch Dob. Or would I just be getting a brighter view of the sky fog?

If I went down the Dob route how do people find star hopping with it? I know that if I move my scope on 1 axis it's always E - W and N - S on the other axis. Doesn't Alt - Az get confusing when you are starhopping by reference to a chart, or Stellarium say, where the orientation changes all the time?
 
 

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In your case larger apertures alone would offer limited improvement for visual observation of DSOs. You will need some visual narrowband filters (UHC or better OIII). Your current mak makes getting larger exit pupil difficult but you need a decent size exit pupil for the filters to work at their best. So a fast 10" f/5 dob will be a good option. However these filters can only help you with certain type of targets mainly nebulae. Galaxies will be difficult to see.

Star hopping with a dob should be no different from your Skymax 127 assuming it's also mounted on an Alt-AZ.

Edited by KP82
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There's no substitute for dark skies. I have a 12" Dob in Bortle 6-7 skies and deep sky stuff is difficult at best. Filters are of no use as they just make things ever darker.

Travelling a short distance I can get Bortle 4 (a narrow band between the light domes of Sheffield and Manchester) and an 80mm scope shows more deep sky objects than the 12" at home :ohmy:

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In Bortle 7/8, visual observation of DSO's other than brighter gaseous nebulae will be rather a waste of time.  I suggest developing an interest in small bright things (double stars, planetary nebulae) or trying EVAA, which can be remarkably effective in showing up galaxies, even from an urban site. For the latter, you'll ideally want a small fast refractor rather than a big Dob.

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33 minutes ago, KP82 said:

In your case larger apertures alone would offer limited improvement for visual observation of DSOs. You will need some visual narrowband filters (UHC or better OIII). Your current mak makes getting larger exit pupil difficult but you need a decent size exit pupil for the filters to work at their best. So a fast 10" f/5 dob will be a good option. However these filters can only help you with certain type of targets mainly nebulae. Galaxies will be difficult to see.

Star hopping with a dob should be no different from your Skymax 127 assuming it's also mounted on an Alt-AZ.

Thanks. I should've said in my post that the Skymax is on an equatorial mount. 
I hadn't thought about exit pupil size before. Did some calculations and realised that even with my 32mm eyepiece my exit pupil is only 2.7mm which presumably will limit any value I can get from a filter?

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14 minutes ago, Mr Spock said:

There's no substitute for dark skies. I have a 12" Dob in Bortle 6-7 skies and deep sky stuff is difficult at best. Filters are of no use as they just make things ever darker.

Travelling a short distance I can get Bortle 4 (a narrow band between the light domes of Sheffield and Manchester) and an 80mm scope shows more deep sky objects than the 12" at home :ohmy:

Thanks - certainly gives me food for thought. I have pretty dark skies within say 45 mins - it's just the hassle of packing everything in to the car, finding a good site, setting up etc.  

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16 minutes ago, Cosmic Geoff said:

In Bortle 7/8, visual observation of DSO's other than brighter gaseous nebulae will be rather a waste of time.  I suggest developing an interest in small bright things (double stars, planetary nebulae) or trying EVAA, which can be remarkably effective in showing up galaxies, even from an urban site. For the latter, you'll ideally want a small fast refractor rather than a big Dob.

Thanks. Small bright things might be the way to go. 
I hadn't thought about EVAA - a whole new area to explore!

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4 minutes ago, Guy65 said:

Thanks - certainly gives me food for thought. I have pretty dark skies within say 45 mins - it's just the hassle of packing everything in to the car, finding a good site, setting up etc.  

Yeah, there's that.  I live in crazy LP (western suburbs of Chicago) and there's really no substitute for heading to darker skies.  I used to have a C8 on an equatorial mount and it was too much hassle to haul places, so I switched to smaller, grab-and-go refractors.  My small fracs have done surprisingly well in B2, 3, 4 skies.

Assuming you prefer to observe at home with your current scope, I'd suggest open star clusters, double stars, and the moon.  I can see a lot of nice clusters here and while I used to consider the moon as an annoyance, it can be quite fascinating if you spend some time studying it.  

I have a couple of nebular filters and they help some at home, but not a tremendous amount.  I am considering getting an H-beta filter for emission nebs as an experiment.

 

 

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I've always wondered this myself, if I ever got a 10-12 inch scope would my viewing be improved in bortle 7? I've dabbled in it a little from a 60mm refractor to a 130pds to a C6, and usually the target I test on is m13. You'd think a concentrated ball of stars would be easy to see, in my refractor forget it. I marginally was able to see a very very dim smudge of a blur with averted vision in the 130pds, and again in the C6. Nothing could be seen dead centre. So I don't think aperture increase in this situation will help at all, it's why I image more. A 10-30s exposure in any of the above scopes shows m13 easily.

Edited by Elp
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Star hopping in a Newtonian is pretty easy if you use a wide angle eyepiece.  I use a 32mm plossl which give a 2° fov.  I just find the nearest bright star on my chart/skysafari, line up on it with my quickfinder, then turn the chart upside down-ish.  That'll match the view from the Newtonian.

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2 hours ago, jjohnson3803 said:

I am considering getting an H-beta filter for emission nebs as an experiment.

You would be far better getting a good quality UHC filter. H beta whilst useful for certain targets is limited in its use.

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2 hours ago, jjohnson3803 said:

Thanks.  I have two UHC filters, but was thinking the H-beta might be a good adjunct.

 

Would certainly be interesting to see how it goes.  I think California and Horsehead are two notable examples, but no idea how they would cope with light pollution.

I found this on cloudy nights which has some good descriptions of how different filters affect (effect?) different targets:

https://www.cloudynights.com/articles/cat/user-reviews/accessories/astronomical-filters/filter-performance-comparisons-r1471

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I live in bortle 4 skies.  The difference between my 10 inch and 16 inch is noticeable.  If i put the light shields on to limit some of the light pollution from the security lights down the road it becomes even more noticeable.  The two filters i use the most are a regular UHC and a OIII, and they definitely help when when chasing the summer nebula in my southern skies.  As to a H Beta.....its good for such a limited number of things and we really have it to look at one thing, i dont know if I would even mess with one in your skies.  

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I wish larger would be better under light polluted skies but as those larger dobs gather more light from fuzzies the also swallow up that much more light pollution, leaving you back at the drawing board.

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On 02/03/2023 at 15:39, Guy65 said:

Hi folks

I have fairly bad light pollution to the South (Bortle 7 or 8 I would guess) and struggle to see anything other than the brightest DSOs with my Skywatcher Skymax 127 (I know that's not an ideal scope for DSOs) which I've had for several years.  I would just like to be able to see more of the Messier catalogue (to start with). 

Would a bigger aperture help with visual observation of DSOs? I was thinking of an 8 or 10 inch Dob. Or would I just be getting a brighter view of the sky fog?

If I went down the Dob route how do people find star hopping with it? I know that if I move my scope on 1 axis it's always E - W and N - S on the other axis. Doesn't Alt - Az get confusing when you are starhopping by reference to a chart, or Stellarium say, where the orientation changes all the time?
 
 

Good advice above. My only addition is that a zoom eyepiece can often help with finding the best magnification to make a DSO stand out - there’s usually a point at which you get maximum contrast between the object and the sky background, sometimes it’s a higher magnification than you’d expect. The downside of zooms is the limited FOV at the longer end of the focal length range (typically 40-50 degrees at 24mm). 

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If it's the Messier objects you're hoping to see, you might find that shielding your peripheral vision from even slight light intrusion, will help you get maximum dark adaption for your site. Doing this and patiently studying the object will give you the chance to reveal detail you'd otherwise miss. If you can't see the object but you know you're looking at the correct area of sky, maintaining your dark adaption using a dark blanket or hood over your head and eyepiece, then moving the scope just a little while using averted vision, can help you to eventually detect it. You may not need nebula filters at all for the Messiers as they are quite bright in the main, and your 127mm Mak should handle them all.

Edited by mikeDnight
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Star hopping is fine, its just a matter of learning and then it gradually becomes natural. Home skies are best for brighter DSO objects, such as the listings in 'Turn Left At Orion'. Aperture will make for improved viewing, as for example; open or globular clusters, planetary nebulae. Dark skies of course are 'where its at' and will make for a broad and significant gain in DSO potential at the eyepiece. An 8" or 10" dob will not be too much hassle to take out on a car trip.  

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I bought a 10" Dob so I could see Messiers from home sadly I have not had any improvement.  I am in the process of trying a couple of places with Bortle 3/4 within 45 mins of me, when I have really clear skies I will take the dob out. When I have not got really good skies I will sat at home Bortle7/8 and use my Tal 100rs and look at double and multiple star systems and clusters.

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Slightly related, but if you had a 10" scope and a 5" scope, both F5, if you picked the eyepiece so that you had the same magnification (say 32mm in the 10" and 16mm in the 5"), would the brightness of the sky look the same?

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On 02/03/2023 at 15:39, Guy65 said:

Hi folks

I have fairly bad light pollution to the South (Bortle 7 or 8 I would guess) and struggle to see anything other than the brightest DSOs with my Skywatcher Skymax 127 (I know that's not an ideal scope for DSOs) which I've had for several years.  I would just like to be able to see more of the Messier catalogue (to start with). 

Would a bigger aperture help with visual observation of DSOs? I was thinking of an 8 or 10 inch Dob. Or would I just be getting a brighter view of the sky fog?

If I went down the Dob route how do people find star hopping with it? I know that if I move my scope on 1 axis it's always E - W and N - S on the other axis. Doesn't Alt - Az get confusing when you are starhopping by reference to a chart, or Stellarium say, where the orientation changes all the time?
 
 

I observe in light polluted Bottle 7/8 skies. Starting with a 130mm newtonian to a 127mm refractor, 150mm & 204mm newtonians and 102mm refractor with a couple of small Maksutovs thrown in.

I found the 8" dob didn't help me observe significantly more objects however extra details were observed in the objects I can see. Globular clusters for instance resolved more peripheral stars. Open clusters looked brighter and more dense due to resolving some of the fainter stars & and the extra aperture gathering more light overall.

In the end I decided to downsize to a 102mm refractor as my main scope because I discovered I prefer observing with an easily managed mounted telescope while also managing my own expectations!

Aperture is king but personal preference and circumstances trump the generic ideal.

Hopefully that makes sense. I'm slightly distracted watching Liverpool stuff Manchester Utd.🥳🤣

 

Edited by ScouseSpaceCadet
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8 minutes ago, Ratlet said:

Slightly related, but if you had a 10" scope and a 5" scope, both F5, if you picked the eyepiece so that you had the same magnification (say 32mm in the 10" and 16mm in the 5"), would the brightness of the sky look the same?

No. The brightness depends on the exit pupil. So the 10" would be 32mm/5 = 6.4mm and the 5" 16mm/5 = 3.2mm. The brightness of extended objects, and therefore the background, is proportional to the square of the exit pupil. 

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