Light Pollution Processing/Dark Sky Site/First Images

[JR1987]

OK so after 2 months of working it all out, I'm finally actually able to start shooting! 

I live in Kent so I naturally headed to Romney Marsh (around the area at least), which is regarded (as far as I'm aware) as a fairly good dark sky spot. But like something out of the Truman Show the northern sky light pollution seems to follow me around.. even down in the Bottom end of nowhere the light pollution in the north was washing everything out..i could *only just* see and attempt to align polaris in my polar scope.

I think the horrible light was from Ashford, which is like 10 miles away but still seemed to have a huge effect. its like you can't escape the LP! 

Anyway, Orions side of the sky was happily dark and Orion was blindingly obvious to the naked eye. so i thought that was what i would pick as my very first attempt at imaging. I went for 2 minutes at 800iso, and I found the subs to have what only can be a film of LP really taking over the photo.. Ill add the photo below. I also took some shorter exposures when testing and the LP wasn't as bad. 

If I'm going to dark sky sites and I'm STILL getting LP, is everyone having to deal with this and edit it out in post processing? does the processing of LP have a detrimental effect to the colours your trying to pull out? Im considering buying a decent LP filter to combat this rather annoying situation but I feel like I shouldn't have to if I'm travelling to darker skies.

(both images roughly cropped to keep them below 1mb to upload into post! Also, i know there is a bit of star trailing and blur etc, still getting used to precise alignment)

one raw 2 Min Sub at iso800 with horrible LP

This is from a 1:30 sub at iso800 with a about 15 minutes of messing around on photoshop to remove LP etc 

[pipnina]

Are you in the middle of a city? Going just 2/3 miles away from the source and the LP gets much weaker and isn't a horrible orangy colour.

[Marky1973]

Hi JR. Don't know what equipment you are using, but I got hold of a Skywatcher LP filter for £30. It's a 2" screw-in filter that fits to the end of my field flattener - I posted about in the post below which shows the difference in results with a very cheap filter - or at least compared to the clip filters!

http://stargazerslounge.com/topic/234757-skywatcher-light-pollution-filter-first-use/?hl=%2Bskywatcher+%2Blp#entry2541103

And it must be frustrating if the light is still getting to you in the depths of Romney Marsh!

Nice images regardless!

[Thalestris24]

Hi

You have to stack multiple subs, in DSS (Deep Sky Stacker), for example and post process. Have a look at some APT previews I just posted in another thread:

http://stargazerslounge.com/topic/236565-full-spectrum-camera-vs-h-a-filter-on-scope/page-7 (bottom of page). LP filters are very useful. I use them but being in a city I still get bad lp.

Louise

[JR1987]

Hi all, 

I took about 20 subs and dark frames/Bias frames. I was just astonished at how even a 2 minute sub can be so orange even when pointing into a dark sky. 

Ill stack them and process and see what happens. should LP be filtered pre or post stack?

[Thalestris24]

Hi

LP filters are attached within the camera e.g. Astronomik clip filters, or in the optical imaging train, either in a filter wheel or attached to a suitable adapter. I think, it's generally accepted that a filter should be fairly close to the camera sensor.

Louise

Edit: It often happens that the atmosphere isn't transparent and can reflect lp from many miles away

[JR1987]

Hi

LP filters are attached within the camera e.g. Astronomik clip filters, or in the optical imaging train, either in a filter wheel or attached to a suitable adapter. I think, it's generally accepted that a filter should be fairly close to the camera sensor.

Louise

Edit: It often happens that the atmosphere isn't transparent and can reflect lp from many miles away

sorry I wrote that badly, what i meant was should the LP be filtered out with photoshop of individual frames prior to using deep sky stacker or stacked first then processed out in photoshop

[Thalestris24]

Hi

You always stack prior to any post-processing. Filtering is done with a physical filter - anything else comes under the heading of processing including certain special functions such as gradient removal

Louise

[wxsatuser]

Just to give you an idea I have moderate to bad LP, don't let it stop you.

Yes a dark sky is most preferable but it's not the end with LP.

I can do upto 10minutes when using both my camera lenses and the Borg at around f/4.

The Canon 60Da always has the Astronomik CLS clip fitted and it certainly allows for longer exposures.

I try to get at least an hour of 5minute subs but look for 2hours if clouds allow.

Here is one of my light polluted images after some processing.

Still learning the processing side of things but I think you can see what can be achieved.

BTW most of my images have horrendous gradients as well.

Don't give up as a decent LP filter will increase exposure by 2 to 3 times.

[dph1nm]

I was just astonished at how even a 2 minute sub can be so orange even when pointing into a dark sky.

Be aware that you are looking at a camera (or software) -scaled jpeg - and these are designed for daytime shots, so naturally they think the background should be bright. If you look at an unscaled RAW image (which is the data you are really interested in) you will find they are pretty black in 2 mins even with lots of light pollution.

NigelM

[frugal]

An awful lot of light pollution can be edited out at the processing stage. Here is a single sub from the stack, along with the processed final image:

[frugal]

I hope you don't mind, but I had a quick go at your 2 minute sub to try to get rid of some of the light pollution and bring out some of the detail. It is a bit blocky as it is a JPEG, but the data is certainly there:

[happy-kat]

That has lots more depth.

I find it hard to keep the nice clear bright stars and smooth and lose the murk and almost made it stars from the background.

[rharrison]

Hello,

Very new to all this still not sure what a sub is.. anyway went to Romney Marsh too the weekend before last, here's a picture with my 1200d through my cheap and pretty nasty Bresser Messier 102mm 600mm fl.

It's 7 x 1 min unguided exposures stacked in Photoshop by just changing the opcacity of each layer to around 40%...

Horrible CA but Romney Marsh is great if you get right in there!

[frugal]

Hello,

Very new to all this still not sure what a sub is.. 

It is short for a "Sub-image" or "sub-frame". i.e. when you make a final image by stacking 30 images together, each of the 30 images is a "sub".

[JR1987]

Ah Frugal, that gives me a lot of hope haha, yes I have been reading the processing techniques in Steve Richards book. Its very helpful stuff as I'm basically new to photoshop. 

I tried stacking all my subs last night and once it had complete I got a bit lost, as what the final image came out as was all weird.. sort of lost my place a little so I'm going to try again and go through some more DSS tutorials.

Rharrision, you came all the way from essex, you must be south west essex surely! Should let me know when you head down threre next, it gets pretty spooky in those dark fields with your mind playing tricks on you, I'm sure you'd agree! 

[JR1987]

This is what I managed playing around a little more with the single sub. I was fairly pleased but it clearly is crying out for more subs to smoothen that grainy look.

[rharrison]

Ah Frugal, that gives me a lot of hope haha, yes I have been reading the processing techniques in Steve Richards book. Its very helpful stuff as I'm basically new to photoshop. 

I tried stacking all my subs last night and once it had complete I got a bit lost, as what the final image came out as was all weird.. sort of lost my place a little so I'm going to try again and go through some more DSS tutorials.

Rharrision, you came all the way from essex, you must be south west essex surely! Should let me know when you head down threre next, it gets pretty spooky in those dark fields with your mind playing tricks on you, I'm sure you'd agree! 

Haha yes it certainly does, I found a great spot though! Although around 2am someone rode past on a bike with no lights on chanting something very strange about being the creator or something which I couldn't quite understand as we were about 100ft back from the road sounded possibly extremist, given we were in the middle of nowhere, really strange!! Luckily I wasn't alone and he didn't see us but It still put me on edge for a while considering whether to use the whole tripod or just the counter weight shaft to beat off the murderers etcetera

The pictures looking better I just hate the over processed look in my images which I inevitably end up with trying to eek out more detail. It's an insanely complex task to get decent DSO images isn't it! but extremely interesting and rewarding. 

Thanks for the 'sub explanation.