First deep sky images

[dark star]

I thought I would post my first attempts at deep sky imaging from the weekend. Not because they are good (they are terrible!) but because I need advice and this may be useful for other absolute beginners.

My main question is can I get any more detail out of these pictures? There is a drop box link at the bottom of the post, which links to two TIFF files. These were stacked in DSS and processed a little. If anyone can improve them given the numerous issues I will be amazed. The main thing is I need a lot more time for exposures as there is only around 8 minutes in total.

To be honest I am quite pleased as I don't have the faintest idea what I am doing and you can see stars in the images and possibly, very faintly, M81 and M82, plus M51 if you search really carefully!

Taken with my old Canon 20d DSLR, equinox 80ed refractor and HEQ5 mount. Camera controlled from my notebook computer using astrophotography tools (APT). 12 pictures stacked and processed a little in Deep Sky Stacker, for M51 and 6 for M81 and M82

The first issue is the black circles, I presume this is dust? I have now cleaned my camera sensor and seem to have got rid of it.

I am quite pleased the stars look reasonably sharp, I spent a long time taking photos of a bright star and adjusting focus by looking at the images on the computer screen. Using the APT focusing aid, FWHM.

The next issue is that if I took exposures of more than around 1 and a half minutes the image was washed out. I assume this is due to my bad light pollution on the outskirts of London and I need a light pollution filter?

I experimented with exposures ranging from 30 seconds to 90 seconds and ISO settings 400, 800 and 1600. How long exposure is needed, for example for M51?

I never intended to go down the slippery slope of astrophotography, as I guessed how hard it would be to take good pictures!

I was driven to it by not being able to see M51 despite a lot of searching. I think it is very hard to see visually under bad light pollution.

At least I have seen it now (I think!), if only in a photo I took and very faintly! Go to is very useful when you can't see the object you want to photograph!

Sorry for going on, but I had a lot of questions. I have more, but will save them for another post!

I quite enjoy taking photos, frustrating as it can be, and learning how to stack and process the images is also enjoyable. Any advice gratefully received.

David

https://dl.dropbox.com/u/82184859/M51stack.TIF

https://dl.dropbox.com/u/82184859/m81%20and%20m82%20stacked.TIF

[Shibby]

Hi David,

These are truly excellent first attempts at astroimaging! Your focus is bang on and you have sensibly limited your exposure time. A million times better than my first (or second... or third...) attempt!

The first issue is the black circles, I presume this is dust? I have now cleaned my camera sensor and seem to have got rid of it.

Yes, dust on the sensor. Flat calibration frames can remove these alltogether.

The next issue is that if I took exposures of more than around 1 and a half minutes the image was washed out. I assume this is due to my bad light pollution on the outskirts of London and I need a light pollution filter?

You definitely need an LP filter. As you say, there is no way to expose for longer without one - also, the LP will be washing out the fainter parts of the signal.

How long exposure is needed, for example for M51?

Well... as long as possible without over-exposing the galaxy core! How long is possible, though, will depend on your LP level and tracking accuracy. (Don't sacrifice star shapes for exposure length! You can recover a surprising amount of signal with stacking & resulting noise removal).

I've tweaked one of your images in Photoshop a bit. They are quite washed out as you realised, but the detail can still be seperated out using levels & curves. Lots more subs would mean this detail would be less noisy. The colourful spots are hot pixels - dark calibration frames will remove these, but with enough subs they would disappear anyway from the stacking algorithm.

[dark star]

Wow! Thanks a lot, I would not have believed it was possible to get that picture from the original picture of M51!

I will start learning about levels, curves and darks!

Also, it is possible to make M51 bigger without losing detail or the image getting a lot grainier, which is very interesting.

I have now got an Astronomik CLS CCD EOS clip light pollution filter (that is a mouthfull!) so I will try some longer single exposures and also longer exposure in total

Thanks for the encouragement!

David

[Jannis]

I gave m51 a quick go as well in PS from the tif file. It's quite noisy, but that's to be expected with that short total exposure time though. Normally for a target like this you'd need at least 1 hour of data to get out some good details without too much noise. Then again, the more the better. Nothing wrong tith 4-5 hours exposure either, lol...

But for 8 min, it's a nice capture i must say. Very good focus, and got some colours too

I'm not very too at this, so a much better result is to be expected from the same file from someone who is good at processing. I'm still in the erly learning process here..

I didn't focuse too much on the noise and fine details here though, only wanted to drag out the galaxy a little from the bright background to see what you've actually captured in that seemingly "useless and overexposed" picture.

Don't giv up at least, it's absolutely data in there, and it's only going to get better from here on!

[todd8137]

yes they look scary when they come out the stacking software once sorted with a few curves and levels and your away

[squeaky]

just tried with PSP X3...

Hmm... can do better

[dark star]

Thanks a lot to everybody for showing me that m51 is there and can be made much more visible with processing.

I have a 3 month trial version of PS which I am experimenting with, I also have RawTherapee which is free which I will try to get to grips with. I am slowly making progress with levels and curves in PS, but there is still a lot to learn! Non of my attempts at processing look as good as the above examples, but I have managed to improve the image a reasonable amount. Next I will have to learn about layers!

I haven't had chance to have another go at m51 due to almost continuous rain and cloud, but hopefully will have another try soon. Imaging is quite enjoyable and the processing gives me something to do when it is raining! I still hope to see m51 visually!

At some point I will try imaging m51 with my 250mm f/4.8 Orion Optics UK reflector as it will be interesting to see the difference in images.

At the moment it only comes to focus with the Canon DSLR with a Barlow, I will investigate a low profile adapter.

David

[Cloudwatcher]

If the dust bunnies and background are removed there is quite a nice widefield view of the stars and galaxy to be seen.

(Although I can't pull out much detail in the latter,I'm sorry to say.)

[Quatermass]

Getting that detail from light polluted London is an excellent result and with more subs dark flats and bias shots you should really be able to get a good shot. If you want some help with ps processing I have put together a series of tutorials covering just about everything you will use in processing your images with ps work your way through them and you will be well on your way. The processing side of imaging takes longer then taking the images them selfs a lot of the time but its fun learning it all.

here is the link to my tutorials.

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[c3po]

Some really nice images, although washed out the detail is there. It seems most had a go with pulling the details out on the M51 image, so i thought i'd be different and try the M81/M82 picture. Close up, it appears that maybe some of the stacking didn't go great as there are quite a few trails, but that didn't detract from teh final cleaned up image.

here's what 5 minutes or so in PS CS4 got me: