Light Polution advice - Am I wasting my time or not?

[NeilFawcett]

So I'm looking into getting a telescope, maybe something along the lines of a Starwatcher 150PDS. One fundamental question I have is, is the light polution in my area going to impact on my ability to see/photograph any (major) deep sky objects? I'm not sure if people are able to give me advice on this, but in an attempt, last night I took some 15 second exposures (1600 iso) with a 50mm lens of Polaris and Deneb. First without any filter, then with a light polution filter.

I'm hoping people can look at the resultant images and give me an opinion if the quality of capture would indicate the 1 minutes exposures (stacked) required for photographing (the bigger) DSOs will be possible?

Deneb (Chose this as overhead so the least light polution)

Without filter - http://img694.images...7285normalc.jpg

With filter - http://img834.images...7291filterc.jpg

Polaris (Chose this as a reasonable amount from vertical so some light polution)

Without filter - http://img69.imagesh...7289normalc.jpg

With filter - http://img837.images...7293filterc.jpg

A random shot from directly overhead

With light filter - http://img268.images...7294filterc.jpg

So:-

1) Do these example in anyway help people advise if I will be able to photograph DSOs with my level of light polution? I'm thinking multiple 60-90 second exposures stacked?

2) Do light polution filters hinder capture of DSOs? You can cleary see less (faint) stars have been captured in the images with the filter. But I suspect another 5 seconds of exposure time might have resolved this? Yes?

3) Any other sort of tests I could do to maybe give a better indication?

Thanks for noob help as usual!

[robbieince]

Hi Neil

I dont think that looks bad at all - you should ber able to do AP and get reasonable results. Of course you'll need a driven mount to allow you to stop the trailing, this itself will let you get fainter stars and more detail.

A filter helps when the object brightness s close to the sky background - so wont really make that much difference on star fields but you will be able to push the faint stuff in post processing much more when a filter is used.

[glowjet]

Neil, rather than a general inquiry your question is loaded towards imaging, as you may have a better chance of response, I suggest we move it to Imaging Tips-Tricks and Techniques

John.

[ollypenrice]

Although I work from a very dark site and have never used an LP filter I would have said that many people on here are imaging under worse conditions than those which appear in your test shots. I stress that I'm no LP expert, I emigrated to avoid it! However, the gradient in the Polaris image (I guess you are at around Lat 51 or so?) is not all that great which is a good sign. You'd need to ask imagers local to you which photographic LP filter works best in your conditions.

Olly

[nytecam]

So I'm looking into getting a telescope, maybe something along the lines of a Starwatcher 150PDS. One fundamental question I have is, is the light polution in my area going to impact on my ability to see/photograph any (major) deep sky objects? I'm not sure if people are able to give me advice on this, but in an attempt, last night I took some 15 second exposures (1600 iso) with a 50mm lens of Polaris and Deneb. First without any filter, then with a light polution filter.

Thanks for noob help as usual!

Your LP can't be worse than mine eg 9 miles from Picaddilly Circus and I've >8M neighbours - I use a big 12" 'fast' f/3.7 equat mounted SCT and unfiltered OSC Lodestar-C in brief exposures and get down to mag 17/18 in 5m exp eg about my longest stacked exposure - check my sig;-)

[pete_l]

Your LP doesn't appear too bad - it's less than mine was when I started imaging.

One comment I would make. You talk about 60-90 second subs. If you can get longer exposures without trailing or saturating the sensor, go for it. The reason is that LP adds a constant background level to images, which your target adds on to. The longer you expose, the bigger the difference between the LP background (which is processed away) and the "good" light from your target object.

[NeilFawcett]

Your LP doesn't appear too bad - it's less than mine was when I started imaging.

One comment I would make. You talk about 60-90 second subs. If you can get longer exposures without trailing or saturating the sensor, go for it. The reason is that LP adds a constant background level to images, which your target adds on to. The longer you expose, the bigger the difference between the LP background (which is processed away) and the "good" light from your target object.

Well, I suggest 60-90 seconds, as I'm assuming worse case scenerio with an EQ5 pro mount only allowing that. If it can manage longer, fine, but I suspect from previous conversations with guidance, that's about as good as I'll get. And then I'd have to stack the images...!?

Would it worth while doing a 90 second exposure with my D90 DSLR (as in my original post) and seeing how those come out? Of course there will be trails without a mount, but would that show more clearly if light polution is an issue or not?

For such an exposure (90 seconds) would I stay with similar exposure settings. eg: F5.6, iso 1600?

[NeilFawcett]

the bigger the difference between the LP background (which is processed away)

Are you suggesting that post processing processes light polution away across the image(s)?

[pete_l]

Yes, there's no point exposing beyond the time when you get trailing, as then all that's happening is the light that should all be in 1 pixel is spread across many so you don't get any increase in depth.

A 90 seconds shot will give you a good idea of what the LP will look like on your final image, so it's something that's worth the effort. It'll also give you some example images to hone your LP removal techniques for when you get the 'scope. Though remember that the longer your focal length (whether with a DSLR + lens of camera + telescope) the darker the sky background appears, so the LP you get through your telescope will be less than what you get with your 50mm lens.

So far as processing away LP, yes - to a large extent it can be removed. That's one of the benefits of imaging for people who live in polluted areas. Even if you don't use narrow band imaging (another method for lessening the effects of LP) it's possib;e to draw out detail that you would otherwise think was lost in the background glow.

[NeilFawcett]

Yes, there's no point exposing beyond the time when you get trailing, as then all that's happening is the light that should all be in 1 pixel is spread across many so you don't get any increase in depth.

A 90 seconds shot will give you a good idea of what the LP will look like on your final image, so it's something that's worth the effort. It'll also give you some example images to hone your LP removal techniques for when you get the 'scope. Though remember that the longer your focal length (whether with a DSLR + lens of camera + telescope) the darker the sky background appears, so the LP you get through your telescope will be less than what you get with your 50mm lens.

So far as processing away LP, yes - to a large extent it can be removed. That's one of the benefits of imaging for people who live in polluted areas. Even if you don't use narrow band imaging (another method for lessening the effects of LP) it's possib;e to draw out detail that you would otherwise think was lost in the background glow.

You mention about doing away with LP in post-processing. But surely light polution filters are useful in the intial capture if only to reduce the problem in the first place?

I'll try and do a 90 second exposure and see how that looks. Thanks!

[pete_l]

If it's any consolation, here's a shot I took from my back garden in Marlow in 2004. It's a 60 second exposure from a Nikon CP5000 PnS. As you can see, the LP looks terrible but using a telescope and judicious photoshopping I could get images of stuff that was impossible to eyeball.

(in case you're wondering, the constellation in the photo is Scorpio)

[pete_l]

LP filters are less useful these days. The one I have (not used in the above ) was only really effective against the Sodium streetlights that you can see giving the yellow glow in the photo. Now we have broadband white lights instead. Also, LP filters do cut out a great deal of "good" light, so you need longer exposures to make up for that.

[NeilFawcett]

If it's any consolation, here's a shot I took from my back garden in Marlow in 2004. It's a 60 second exposure from a Nikon CP5000 PnS. As you can see, the LP looks terrible but using a telescope and judicious photoshopping I could get images of stuff that was impossible to eyeball.

(in case you're wondering, the constellation in the photo is Scorpio)

Mate! I'm just up in Flackwell Heath, a few miles away from Marlow

I'm surprised with a 60second shot you can't see trails? With those 15 second ones of mine you can see them. But maybe that's because I was a littme more 'zoomed in'?!

[NeilFawcett]

LP filters are less useful these days. The one I have (not used in the above ) was only really effective against the Sodium streetlights that you can see giving the yellow glow in the photo. Now we have broadband white lights instead. Also, LP filters do cut out a great deal of "good" light, so you need longer exposures to make up for that.

Well I was using a Starwatcher 50mm light polution filter. Comparing with/without it seems to help, although it does seem to reduce the overall exposure?

[pete_l]

There are trails in the original, but I resized this to squeeze onto the web page.

[Jessun]

Your LP looks to be a lot less than what I usually battle. All my images in my gallery is from a city centre of a large city (close to 500.000 inhabitants).

It's a pain to be honest - but in my limited experience a filter does more harm than good. Try processing the LP out. I use a colour camera and no narrow band stuff. Sadly.

[zakkhogan]

hi neil here are a few shots i took from my home.

2 shots taken of the sky we're 3sec exposures (one of which you can see the golden arch nebula)

and the other 2 (dumbbell\ring) are 40 x 15sec exposures

you can achieve a with processing

I hope this helps

[NeilFawcett]

hi neil here are a few shots i took from my home.

2 shots taken of the sky we're 3sec exposures (one of which you can see the golden arch nebula)

and the other 2 (dumbbell\ring) are 40 x 15sec exposures

you can achieve a with processing

I hope this helps

That's brilliant help thanks!

I was looking at those picks wondering where the golden arch nebula was though for a while

Regarding the latter two (dumbbell / ring) what equipment did you use? And why 15 second exposures and not longer?

[zakkhogan]

I used a Celestron CPC800 (SCT) with a f6.3 focal reducer and a canon eos.

I don’t own or use a LP filter

The reason i only do a 15sec exposure is my telescope is only set for altaz so any longer (with the focal reducer attached) I start to get star trails.

When im using the scope at F10 I can get up to 30sec.

If you are getting an equatorial mount you can get much longer exposures, provided it’s polar aligned correctly.

You will get the bleed from the street lights, but you can process it out to a degree, but the longer the exposure the more light you are getting overall, stars and street lights included

Dont let street lights spoil you fun or interest, we sadly cant get away from them completely but we make the best we can

[zakkhogan]

if i get time, when i get home i'll upload a copy of the Dumbbell with the LP included.

[Zakalwe]

*sigh* I wish I had skies with as little LP as the OP....

[zakkhogan]

as promised,

before and after processing shots of the dumbbell neb..

[laser_jock99]

Narrow band imaging works if the LP is bad- this photo was shot low down in the orange haze using a 7nm H-alpha filter. Not a great photo per se, but not considering there was nothing to see visually

M8 Lagoon Nebula Sagitarus 180s

[NeilFawcett]

as promised,

before and after processing shots of the dumbbell neb..

Jesus! What did the processing involve?

[zakkhogan]

when you stack in deep sky stacker it basically produces a black and white image, therefor a nice black sky, but a white nebula, (the colour information is still attached to the image just turned down)

when you move to your editing software ie gimp\photoshop you can reintroduce the colour.

I draw a mask round the nebula and the slowly introduce the colour of the selected area, tweeking with the burn\dodge tool as needed, leaving the background nearly in mono.

once happy with the main focus of the image you can do the same to the background, change the colour as necessary.

its not to hard to do, and there are some really good tutorials on youtube and in this forum