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Hi all,

I got a Lightbridge 10" dobsonian a few months ago and while I'm very impressed with what I can see with it, I can't help thinking it should be able to do better. I'm struggling to pick even Messier objects up with it. I'm just wondering if this can be all light pollution or if I'm missing something else completely.

With the naked eye (I consider my eye sight to be good) from where I am on the edge of a smallish town, the Milky Way is visible only at zenith and you have to really be looking for it, M31 is not a naked eye object (at least not as anything more than a point light), Ursa Minor is invisible save for Polaris and maybe a couple more stars (little plough cannot be seen in full). Orion Nebula M42 is visible just.

With the scope, I can get great results from star clusters, like the Messiers in Auriga. Outside M42 and M31 though I can't get any results from nebula or galaxies. M1 Crab Nebula, M78 in Orion and the Owl Nebula in Ursa Major come up as extremely faint smudges, almost needs averted vision. Other targets I've looked for don't show up at all. I have an Orion Ultrablock filter and this makes a noticable improvement on M42 which looks fantastic even without it, and it makes the background sky noticably darker, but it doesn't seem to improve the other objects or bring new objects into view.

Does this sound about right? I'm not expecting to get detailed views on anything and I'm not dissapointed; I'm happy to see a faint blur if I know what it is. But I thought I should be able to at least pick things up, especially Messiers. I'll admit I've only really had the chance to point at certain parts of the sky due to the almost permanent cloud cover in the UK:(, mostly around Orion and that general area as I know this part of the sky well. So there are probably many great targets for me I just haven't tried yet.

Can other factors limit what I can see? Collimation for example? I know the Moon hits the sky bad. I don't have a cover for the Lightbridge, its open at the moment, would this make a difference by blocking stray light? Or have I just vastly underestimated the light pollution on the edge of a town?

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Don't own a Dob/Newtonian but I would have expected you to have been able to see more then you describe.

I live in a town and M31 is just about a naked eye object. If you look in the right place you can tell something is there, through binoculars (8x42) you can see a smudge.

I would therefore guess, open to disagreement here, that there is something out in the set up. Collimation being the obvious one. Hate to say it but I would start checking out all possibilities and set it up as best as possible.

The other thing is have you got a finder scope and is it well aligned?

The "problem" of a dob is that you have to point the thing at the target, even if off by a little the target doesn't appear in the field of view, so you see nothing - just what you are describing. M42 and M31 are fairly big so easier to get in the field of view - so are clusters. M1 is little and faint.

I assume that you are looking initially with a nice long focal length EP? Have to ask as people can start off thinking "Fit the highest power EP I have and see everything BIG". It doesn't work like that.

Out of interest where about are you?

Helps to get some idea of the light polution you may be talking about.

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Don't expect too much - galaxies are always fuzzy blobs, and any detail needs to be teased out. M1, M78 and M97 are all at the less impressive end, certainly compared to M42. Give the Eskimo Nebula and M81 a try

If you can see Milky Way at zenith then your sky is better than most peoples' but could still be better. You've probably got a limiting mag of around 5. In a rural spot you could get a magnitude fainter, equivalent to increasing your effective aperture by over 50 per cent.

Collimation has no effect here, light grasp is everything. An open-tube scope won't suffer too much if there's fairly low light pollution, but your eyes can never get fully dark-adapted in those conditions and this affects what you can see.

Try putting a hood over your head to block out all stray light at the eyepiece. Avoid looking directly at any light source (except ones in the sky!). It takes quite a while for dark adaptation to become full, so be patient with the objects you look at.

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Smoore,

Is there any light pollution coming from not-so-obvious sources, such as lights streaming from your windows, neighbour's windows, etc?

If your house is the culprit, I can recommend black-out roller blinds...it seems your sky is relatively dark, but something may be affecting your viewing from lower down.

Are there any hallogen lights or external lighting?

Like the others have said here, check the scope's collimation. EDIT: disregard this sentence :)

Is your telescope a truss tube, and do you have a black shroud over the truss rods of the OTA? The shroud can aid in preventing stray photons from hitting your mirror!

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Thanks for the responses everyone.

I'm in Derbyshire, from what I've seen on maps not the best place in the UK for light pollution, but I myself am in a good spot.

Outside, my garden is long so I'm quite away from my house though theres some more at the other end, the brightest ligets to me are window lights, I know its not ideal but its probably better than nearby streetlights.

Without boring you as to why, its not always possible for me to set up outside, I sometimes poke it out of a window thats facing diagonally upwards and South (from an attick) instead. I know windows aren't ideal but its better than not doing it, and the only thing it seems to hurt is using high magnification which I'm only using on the Moon/planets anyway. When I use the scope like this the only light that reaches me is the sky so my eyes can probably adapt better if anything. I make sure to wait about half an hour before attempting very faint objects to give my eyes some time.

The eyepiece I use is a 2" Meade 26mm QX wide angle. I have another eyepiece for higher magnification but almost never use it outside Moon/planets. Is this eyepiece ideal for light gathering or is there room for improvement?

Yes my scope is open truss tubes and I have no cover, I'm imagining this is an area for improvement?

I'll keep an eye out for Eskimo and M81 thanks for that.

I've heard the more you look at things the better you get at it, and I'm finding this to be true with details on the Moon, I think one problem I've got is that I've had very little chance to use the scope at all, I can count the clear moonless nights I've had with one hand. My finder scope (red dot finder) is something I'm still getting used to using, again I think I need some time with that one.

Thanks for the input, much appreciated.

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You're doing all the right things and should be OK with that EP. Viewing from indoors is a no-no on planets as you realise, but for DSOs shouldn't be too bad if the sky is dark enough, and you've evidently being getting some good results. So I'd just say - lucky you, and stick at it. Wish I could see the Owl Nebula from indoors!

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Light pollution is most likely to be the issue. I am in the (unfortunate) position of being someone who has moved away from a rural spot with no LP to a place where my limiting Mag is at best 5.1 / 5.2. The difference is enormous with galaxies and nebula etc. because it is the darkness of the background that really brings DSOs to life.

There are some things you can try:

1 - If you have a truss style scope then get a light shroud. This really does boost contrast.

2 - Get a slightly higher mag widefield eyepiece. A 20mm EP will improve things over the 26mm QX

3 - Get an OIII filter for nebulae. This can make a huge difference for objects like M42 and planetary nebula

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Your viewing conditions sound similar to mine and the results you describe are about the same as the views I'm getting through my 10" scope on an average night. I get the occasional better night but these objects are faint - even with 10" of aperture. I you can see the Owl Nebula without a filter then you are doing OK believe me. The Ultrablock, other narrowbands and OIII filters are really effective on planetary nebulae, make some difference on other nebulae but no difference on galaxies and clusters. You will start to see other DSO's as you get used to picking out these even fainter objects - some of them only really hint at their presence, even on really good nights.

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This is exactly what I've noticed with indoors, planets are a no but DSO's are unaffected. If anything I'm staying warm and cozy and eliminating lights at the cost of only getting part of the sky (a good part at that). I got owl nebula outside, it might even have been the nearby galaxy, I just assumed the nebula is more likely.

What advantage would a 20mm eyepiece give me? Is the slightly higher mag (x~63) more useful? I've been wondering about my 2" 26mm eyepiece actually, if this is giving a wide view and the light exiting the eyepiece is wide then my eyes are probably picking up less light than if it was a narrow output that can all get through my pupil at once?

Am definatley going to look into a light shroud and OIII filter. Can OIII filter and Orion Ultrablock stack together too as neither are blocking the light from nebula? I've noticed Ultrablock darkens the sky a lot but not completely.

Thanks for the input again, its nice to hear what sort of results other people are getting as well.

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For viewing techniques in light polluted areas. Last year an excellent discussion of this topic was on one minute astronomer. Here are links to the interview with Rod Mollise on urban viewing with light pollution:

Urban Observer’s Survival Guide, Part I | One-Minute Astronomer

Urban Observer’s Survival Guide, Part II | One-Minute Astronomer

Urban Observer’s Survival Guide, Part III | One-Minute Astronomer

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I can just make out M31 as a smudge and thats pretty much it for my deep sky observing.

I have a pair of Celestrons 10x50's with LPR filters built in. Helps to darken the background glow. I may invest in a Baader filter for my ep's

Here is a good LP image.

Regards

Matt

post-18805-133877429774_thumb.jpg

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What advantage would a 20mm eyepiece give me? Is the slightly higher mag (x~63) more useful?

I sometimes find it hard to locate the fainter DSOs with the 26mm in light polluted skies. A 20mm or thereabouts can help in tracking those fainter objects down. I use a 17mm Baader Hyperion. My best views of many DSOs come at Mags of x140 to x215

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Best EP for DSOs really depends on the scope, and the sort of DSOs you're looking for. Most relevant factor is exit pupil (aperture divided by magnification). But there is no general agreement on what is the "right" exit pupil - this again depends on what you're looking at.

When I was doing Messiers etc with an 8-inch dob at a dark site I found a 20mm plossl my most useful eyepiece (mag x60, exit pupil 3.3mm). When I started using my 12-inch for run-of-the-mill Herschel galaxies, I found an 11mm plossl more useful (mag x136, exit pupil 2.2mm). At the moment I'm mainly doing galaxies which are very small and faint (Hickson groups, Abell clusters etc), and find the best EP to be a 6mm TMB (mag 250, exit pupil 1.2).

On the whole I'd say the smaller and fainter the DSO, the smaller the exit pupil you want; but in light-polluted skies you probably want to err on the side of small exit pupil to increase sky contrast. So there is certainly an argument for using a focal length shorter than 26mm, though Messiers are large, bright objects by usual DSO standards, and are eminently viewable at low power.

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Your naked eye view sounds spot on for a badly light polluted area. From our previous house i couldn't see Ursa Minor either and M45 was only visible on the rarest of nights. We lived at the house for 12 years and probably only saw M45 naked eye 6-7 times. I did see the Milkyway twice in that time. On both occasions it was due to a neighbourhood wide power failure.

Amazingly i still had some enjoyable observing sessions there, even DSO's. Using a higher power eyepiece really helped increase the contrast on the smaller objects. Low power just seemed to work against me.

Russ

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Whoo hoo its clear:hello2:

Have just seen Eskimo nebula, got some very good results from that, small but reasonably bright and could see that it was a bright core with a fainter surrounding, was well impressed. Looked a lot better than other targets I've picked up before, and this was with an almost full Moon just popping up.

I tried my 12.5mm (x102) eyepiece on it and it looked better on that, I can see now how higher mag can increase contrast, the sky was a lot darker on this eyepiece while the nebula and stars weren't any fainter, guess I need to find the right balance for different objects.

Looks like the "thing I've been missing" just might be how I've been selecting targets and how I've been looking at them too, and not with my setup. I know my RDF isn't perfectly alligned, I'm still getting my head around how to use it right anyway, guess this will come to me.

Well the Moon's really taking over the entire sky now, might stick to brighter things, want to see how far Vesta has moved since I last looked at it anyway.

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