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astromartian

First serious attempt DSLR single exposures of Deep Sky objects.

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I got some cracking single exposure shots of Deep Sky objects today after a decent polar alignment. The culmination of everything I’ve learnt so far; a lot of reading and practice. I was totally blown away by the colours in the Orion Nebula which looks like a grey whisp in the eyepiece. 30 seconds of the DSLR sensor sucking in photons made a big difference. All taken using ISO 200 (apart from the double cluster) and 30 second exposures.

My questions:

  • Most of the stars are smudged, I tried my best with alignment, is there anything else I can do to minimise this?
  • Are the settings ok? I noticed more detail but also more light pollution using ISO 400 in the double cluster.
  • Will the shots get better and less smudged when I start stacking?

Thanks in advance.

P.S. The full size shots can be found on my blog - http://astromartian.wordpress.com/

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post-21891-0-98438100-1390529878_thumb.j

post-21891-0-88955300-1390529886_thumb.j

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Also... the images look grainy and low quality. I'm not sure how they compare to the RAW files but could this be due to conversion to JPEG or perhaps low resolution of my DSLR sensor or is it just a feature of low light photography?

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You could try ISO800 or 1600 and cut the time to 20 secs to see what kind of trailing you get.

Stacking can hel, but not cure mislagnment

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nice work! About to make my first attempt at prime focus too, as soon as the skies clear!

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I got some cracking single exposure shots of Deep Sky objects today after a decent polar alignment. The culmination of everything I’ve learnt so far; a lot of reading and practice. I was totally blown away by the colours in the Orion Nebula which looks like a grey whisp in the eyepiece. 30 seconds of the DSLR sensor sucking in photons made a big difference. All taken using ISO 200 (apart from the double cluster) and 30 second exposures.

My questions:

  • Most of the stars are smudged, I tried my best with alignment, is there anything else I can do to minimise this?
  • Are the settings ok? I noticed more detail but also more light pollution using ISO 400 in the double cluster.
  • Will the shots get better and less smudged when I start stacking?

Thanks in advance.

P.S. The full size shots can be found on my blog - http://astromartian.wordpress.com/

attachicon.gifPleiades.JPG

attachicon.gifOrion Nebula 30s.JPG

attachicon.gifDouble Cluster ISO 400.JPG

attachicon.gifbeehive cluster.JPG

attachicon.gifthe christmas tree cluster.JPG

A quick look seems to suggest the "smudges" are around the edges..suggesting this is Coma..your using a newtonian? If its trailing due to poor alignment then all the stars trail the same and in the same direction. Coma makes stars around the outer look like little comets that point towards the centre.

ISO 800 is usually around the optimum..sens increases as does noise but signal/noise is abt the same. Higher ISO tend to increase the noise more than the signal (in proportion)

The aim of "stacking" is to reduce the noise (by around sq root of number of stacked images). It should not affect anything else, but you do have to select the good images and reject the poor ones (the s/w usually does this for you but dep on what s/w you use)

LP can be taken out in post processing to a large degree and/or you can use a LP filter in the optics. The LP filter lets you take longer exp (up to limit of where trailing comes in) without the sensor becoming saturated.

Good pics!!

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A quick look seems to suggest the "smudges" are around the edges..suggesting this is Coma..your using a newtonian? If its trailing due to poor alignment then all the stars trail the same and in the same direction. Coma makes stars around the outer look like little comets that point towards the centre.

Firstly, thank you for the kind words and all your advice, it's very constructive.

I just wanted to ask (being lazy and not looking it up) what is Coma and how do I correct this?

Yes, I am using a Newtonian.

Aside from the above I'll try ISO 800 and see how that works out next time we get a clear night.

I'm sort of hooked now!

Thank you again.

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Have a look for coma correctors, it's basically a lens - between camera and telescope, to cure coma which is what causes elongated stars towards the edges of the image.

I tried mine for the first time last night - definitely helps. If blurred stars are only away from the centre and they are sharp in the middle your alignment is good enough for your exposure length and the corrector will cure the rest.

You should be able to crank up the ISO, take a bunch of images and stack - but how high you want to go depends how good your camera is at noise.

The other thing, I think (I'm learning too) you can crank up the exposure to the point of some light pollution being captured, don't worry about that - as it can be corrected when you process the RGB levels and curves.

Good luck. It's very addictive (aka expensive) once you get started...

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At similar focal length, I get about 75% useable shots at 30sec with an HEQ5 (although you have larger pixels on the D40, so you should do slightly better). Periodic error kills the rest. To overcome that you really need to guide.

NigelM

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I did some shots of the supernova in M82 last night, due to having minutes before clouds came along I did them unguided.

I pushed it up to 45s (using a 1000mm focal length 200mm tube) and it seemed ok. I pushed the ISO up, even saw M82 quite visibly with a 10s exposure at much higher ISO. Not all cameras are equal though for noise, some much better than others - you'll need to find a good compromise which depends how many subs you can get etc. 

I'd start around ISO 800-1600 and about 30-40s and get say at least 10 good subs, stack them and process the result - see what you can get.

For my best M42 I took about 10 x 3-4min subs and that really starts to bring out all the detail, but then you really need guiding - or you could try drift alignment, but it's going to be a challenge and time consuming! I'm not that skilled so never tried it myself, it sounds difficult.

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I did some shots of the supernova in M82 last night, due to having minutes before clouds came along I did them unguided.

I pushed it up to 45s (using a 1000mm focal length 200mm tube) and it seemed ok. I pushed the ISO up, even saw M82 quite visibly with a 10s exposure at much higher ISO. Not all cameras are equal though for noise, some much better than others - you'll need to find a good compromise which depends how many subs you can get etc. 

I'd start around ISO 800-1600 and about 30-40s and get say at least 10 good subs, stack them and process the result - see what you can get.

For my best M42 I took about 10 x 3-4min subs and that really starts to bring out all the detail, but then you really need guiding - or you could try drift alignment, but it's going to be a challenge and time consuming! I'm not that skilled so never tried it myself, it sounds difficult.

Thank you for your reply.

Have you got a pic of M82? I'd like to see it.

Well I'll push ISO up next time as you suggest and see what I get. I'll try to get multiple shots and give stacking a go; it is the next thing to try. From what people above have said it seems that alignment is fine and it is Coma correction which is needed so that's good news. I think 3-4 minutes will be pushing it definitely unguided but I'll test that too.

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The other thing, I think (I'm learning too) you can crank up the exposure to the point of some light pollution being captured, don't worry about that - as it can be corrected when you process the RGB levels and curves.

Good luck. It's very addictive (aka expensive) once you get started...

I'll bare that in mind, I was definitely paranoid about getting too much light pollution into the shot and after taking a shot with higher ISO I decided it was too much. Now I know not to worry about it too much. I'll invest in a light pollution filter at some point.

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Thank you for your reply.

Have you got a pic of M82? I'd like to see it.

Well I'll push ISO up next time as you suggest and see what I get. I'll try to get multiple shots and give stacking a go; it is the next thing to try. From what people above have said it seems that alignment is fine and it is Coma correction which is needed so that's good news. I think 3-4 minutes will be pushing it definitely unguided but I'll test that too.

Only this, which I took to really to see the new supernova in M82. It was a stack of about 9 x 40s, at maybe ISO1600 I think. All I did was a quick polar align, no guiding or anything more. Subs then through DSS and tweaked levels in PS.

I think to image this nicely you'd really want 20 or more 5 min exposures etc, but just as I got guiding working the clouds appeared for good, game over!

So, this might give you an example anyway for what you might end up with using M82 as a target and unguided short-subs. On a DSLR at 1000mm FL tube M82 is quite small, hence it can be a bit pixellated when blown up. It's a trade-off though, trying to get alignment or guide a much longer FL tube is going to be increasingly difficult and eat into your max sub time.

12108857563_102d4c364e_c.jpg

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I'll bare that in mind, I was definitely paranoid about getting too much light pollution into the shot and after taking a shot with higher ISO I decided it was too much. Now I know not to worry about it too much. I'll invest in a light pollution filter at some point.

I have had subs that are very bright orange and still managed to pull lots of data off them.

Like this before and processed.

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post-32578-0-70125700-1390564310_thumb.p

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All this advice will serve me well when I get around to using my new camera (whatever that will be ) once I have purchased it.

Looking forward to doing some stacking.

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Like Alien 13 says, but ALL my subs looked that colour! I was horrified but it processes out surprisingly easily.

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It really does look too good to be true. I have to wait until I make my own to believe it.

Sent from my HTC One X using Tapatalk

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My first go at stacking based on all your valuable advice! I had a go at Orion Nebula.

Well it took me 5 months to get the telescope out again but I really went for it; stayed up till 1:30 am taking 10 lights and 10 darks.

The setting I used were as follows (I included lots because I have no idea if anything I set is wrong):

ISO 1600

30 sec exposures 

Long exp. NR off

Hight ISO NR Norm

RAW

Color space sRGB

Non-CPU lens data set to Focal length 1000mmm

Maximum aperatre F6.3 

Spend further 4 hours trying to stack and edit and finally came up with this today. Can't think how much time I've spent on this in total and after that epic I think I need another 5 months to recover.

Stacked in DeepSkyStacker and clicked around frantically in Photoshop to try and make it look decent

There is too much red which I couldn't get rid of and I think I need many more shots.

Let me know what you think and what I did wrong.

post-21891-0-29056500-1416071204_thumb.g

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I think I've become slightly addicted after creating this picture; I'm almost contemplating skipping a party to get the scope out.

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and clicked around frantically in Photoshop to try and make it look decent

I see you have truly mastered this dark art. LOL ;)

Great improvement.

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That's very good. Stacking is definitely the way to go.

I can see you've used Lights and Darks, but not Bias or Flats frames.

Bias frames are easy to get, so I'd suggest you include them in your next project.

Flats are a bit more tricky to get but they will improve your pictures significantly and make your post-processing easier (less need to get rid of vignetting or dust bunnies)

Nice work. Keep it up :)

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