Lightpolluted M81, m51, m27

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Decided to fight off some sleep and take the opportunity to try capture some fuzzies.

Equipment.

Scope: Nexstar 102 SLT

Camera: unmodded 1100D

ISO: 800

Exposure: 30s

Locaction: Malmö, Major city in Sweden

Still trying to learn post-processing...

First one is M51. This turned out really horrible. The lightpollution was to much for me to handle.

About 15 frames stacked

http://imageshack.us/photo/my-images/545/m51v1pub.png/

Next is M81

I am quite happy with M82 and that I managed to capture NGC 3077. But I´m not happy with M81

About 10 stacked

http://imageshack.us/photo/my-images/823/m81v11pub.png/

Last is M27. About 10 stacked.

http://imageshack.us/photo/my-images/836/m27v1pub.png/

//Peter

[malc-c]

Pete, once you've uploaded the images, right click on them and select the "copy image location" then insert that URL between the "[img}" tags by clicking on the small picture icon where you are entering the post to display the images in your post.

EG

Makes life easier, and stops stacks of popups for poker / dating etc !! that always plague image shack and other sites like them

Nice images by the way,

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Thanks.

Uploaded the files here instead.

[Gina]

Great And a great start - there's plenty of promise there The main benefit in the process will be Levels, appiled to the individual red, blue and green. That will both remove a lot of the light background and at the sam time remove the magenta colour cast. Mine look the same when I start (or worse). Then you can apply Curves to boost the fainter parts (lift the curve near the right hand side about a third of the way up until to get experience and can apply more complicated curves). After that there are all sorts of things you can do to correct the image. But I find I use Levels and Curves several times to bring out the detail.

It looks like you haven't used flats and some 20 or 30 of those will even out the variation in brightness. Darks will remove a lot of the noise that come up when you stretch the image to bring out the detail. And finally, to further reduce the noise a bit, bias frames.

Hope that helps - feel free to ask questions - we've all been learners and most of us still are

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Thanks alot Gina!

Actually I did use flats, darks and bias (20 flats, 20 bias and 10 darks). :/

Guess I need to retake the flats?

The original tiff I got from DSS looked quite OK with almost no gradient, but curves "fixed" that for me.

You can apply curves to the color channels aswell? Ohh, did not know that.

Will try that when I get home. I just tried some minor color replace to bring the red down on these.

Is there a max too how many "curves" you should apply?

I did it in small steps about 10-15 times in these images.

When I do the curves, eventually the histogram gets split in 2 (2 spikes).

Is this normal?

Cheers!

//Peter

[Gina]

Thanks alot Gina!

Actually I did use flats, darks and bias (20 flats, 20 bias and 10 darks). :/

Guess I need to retake the flats?

The original tiff I got from DSS looked quite OK with almost no gradient, but curves "fixed" that for me.

You can apply curves to the color channels aswell? Ohh, did not know that.

Will try that when I get home. I just tried some minor color replace to bring the red down on these.

Is there a max too how many "curves" you should apply?

I did it in small steps about 10-15 times in these images.

When I do the curves, eventually the histogram gets split in 2 (2 spikes).

Is this normal?

Cheers!

//Peter

Yes, if you overdo the curves you'll end up with too few brightness levels as you've noticed. You have to know when to stop I apply the curves to the whole image and levels to individual colours.

[Jessun]

Hello Peter! Your stars are nice and round so I'd try to take longer exposures. I'm not good with DSLR's (or any camera haha) but you should be able to do 2-3 minute exposures. Once you've established how long you can go you take PLENTY of them. You'll be amazed what difference it makes to the processing stage! With plenty I mean hours in total :-)

Nice work, keep them coming!

[AlexxxAA]

Great stuff Peter! Youre into a great start with the DSLR. Like Jesper above said, your stars are looking nice, so you can probably go for longer exposures. I also recommend getting a CLS clip for your camera. Check optcorp.com or whoever you buy your equipment from. Its a little pricey, but its well worth it if youre going to take pictures from like polluted areas. This will allow you to take longer exposures before the pollution starts becoming apparent. And even when you start taking 1, 2, or 5 minuted exposures... the image processing will wash away the pollution that start coming up on your filtered images once you stack them.

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Thanks Jessun and AlexxxAA.

I will try and push my exposure abit extra.

Does the CLS work with galaxies aswell?

Or is it just nebulue?

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Did some remakes. Funny kinda. Either I get it too red or too green.

Anyone know a good technique to reduce the grain?

[AlexxxAA]

The CLS clip works for both nebulas and galaxies. However I recommend dedicating a little more time into each individual picture. Maybe atleast an hour's worth of exposure. Especially for galaxies like m51 since they're surfaces are so dim.

Here is one I tried last year of m101. I know it's not great, but it's an example of using the CLS clip under severe light pollution.

[farunj]

The newer ones look good!!

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Thanks Farunj.

AlexxAA: I will see if I can get hold of one of these.

I do have a LPR filter. Abit reluctant to use that thou, since everything turnes very blue.

How many 30s exposures can you take before it amounts to more or less nothing?

Or is it more "the more the better"?

[AlexxxAA]

Actually with the CLS clip the images come out blue as well. You need not worry though. When you stack your images on DeepSkyStacker or whatever you're using, that color gets washed out and you get a perfectly dark image that you just need to fix the levels and curves in Photoshop. So you might want to give the LPR filter a try once and see how you like it.

In terms of exposure, the longer the better. If you can go up to 45sec or 1min without guiding that would be great. and the more the better. If you check other people here in these forums, they spend 3, 5, 10 or even more hours of exposure. Its just what you are willing to invest on a single object.

Unfortunately when you are using short exposures, in reality the combined exposure of the images is less than what it really is. There is an equation somewhere that someone here told me once. But for example, if you take 120 exposures of 30 seconds, that is 1hr worth of time, but image-wise, it is only worth about 20minutes of total exposure, maybe even 30 minutes. So it is a little better to take longer exposures because they add up better.

[Anweniel]

I think you have done very well and as others have said you could probably do with a lot more exposures if you want to eek out a bit more detail. Getting off to a good start though

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Thank you all for the kind words and all tips.

I did a new image run of M51.

This time I took 100 30s exposures (about 1 hour).

64 of those got stacked and here is the result.

I think (unless it is some odd artifacts) i got 2 fuzzies aswell.

[Anweniel]

Indeed you do and what a difference eh? good job

[Chris]

I think your doing very well considering your using a single arm alt/az mount and an Achromatic refractor, well done! I wonder if you can get away with 45-60 second subs before field rotation kicks in with your alt/az mount, or will this be pushing things too much?

[AlexxxAA]

Nicely done! As you can see the extra work and time has brought out much more detail on M51 and you did indeed capture some extra fuzzies.

Did you use the filter this time? Your background looks darker this time around.

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Thanks all.

No I didn´t use a filter. I have got my hands on a Astronomik CLS but haven´t recived it yet.

Perhaps was more the fact that I lowered the ISO to 400 and way more careful curves and levels.

I also aligned the RGB channels from start and not when they got out of hand.