first go at m27

[cal1985]

hi all, this is my first try at m27, it was 5min subs x 15 with 8 darks. taken throught a skywatcher 130/900 and canon 300d unmodified, guided with a skywatcher synguider through a celestrion 80 please can you comment on processing and any advice or tips you would make.. the more critism the better ! i want to learn more and have images that alot of you get... but need to learn first !

many thanks cal

[nmoushon]

Not bad for a first go. Flats would help tramendously with the noise as well as dust bunnies that you got going on. Other than that more lights and more darks will really help it.

[Spikey]

Very good for a first go Cal

Flats won't help with the noise much but they will help to get rid of the vignetting & the defects you can see.

Take loads of lights, as many as you can get and this will cut down your noise significantly. Taking darks will further improve the noise but it's diminishing returns and always debatable how many to take; 20 or so would do the trick.

[Gina]

I agree That's what you need to do. Great start

[RikM]

I think that's a great first effort. 5min guided subs on an EQ2 at 900mm focal length. Hat's off

As previous, lots more subs and darks and sets of flats and bias would help make the processing easier. The colour is good though and you can see some retained in the stars as well which not always easy with a DSLR. A Bhatinov mask would help nail the focus as well, although it looks pretty good already.

Keep at it

[Coco]

What a great start!! well done

[ollypenrice]

Yes, well done. More subs, darks and flats... The best tool for sorting the background is DBE in Pixinsight.

But if you use Photoshop there's the plug in called Gradient Xterminator which would help with your background sky.

Olly

[Mark72]

Well done for the first shot!

You definitely need flats to remove dough-nuts. I'd also suggest to work more on focus. Perhaps guiding 5 minutes is a bit too much for a start and for such a bright object.

For post-processing you may pay more attention to background. As Olly suggested PixInsight is a great friend of all beginners here. This may be you best AP investment along with Bahtinov mask.

As aside, there is a free application to make sure you get a critical focus - http://www.njnoordhoek.com/?p=325. Your stars will never look like melons after this.

Mark

[Gina]

As aside, there is a free application to make sure you get a critical focus - http://www.njnoordhoek.com/?p=325. Your stars will never look like melons after this.

Mark

Thanks for the link Mark I've been meaning to look that up and give it a go.

[cal1985]

thank you all for all the input this will all help me a great deal.. is there a avarge amount off lights i should be taking to get a good result or does this depend on condtions ie weather. and object? also i understand lights and darks and i belive flats are exposures of a very short time and through a white tshirt but i dont understand what this acturally does and have no idea what bias are?

[LDUNN1]

Hi Cal, you are well on the way down the slippery slope that is astro imaging :-)

The good news is that your tracking / guiding looks okay, so the data collection looks fine.

.....and data collection is only half the story though. The other half is how you process it. I'm still very much learning this art myself, so this seems to be a bit of the blind leading the blind. Lets go through the processing steps required to move this image forward.

You probably noticed some dark dots spread around the image - these will proably be dust somewhere on your optical path that is causing out of focus dark circles. You may want to check your optical path for dust. You can use the healing tool to process these out, but it takes time & it is all too easy to create new stars in the cloning process!

Next you probably noticed the uneven illumination - the dark corners relative to the centre, otherwise known as vignetting. You can process this out.

You may want to investigate taking light flats in future - without disturbing the camera relative to the optics, put the 300d on 'AV' mode, cover the front of your scope with a clean white piece of cotton, make it taught (an elastic band will hold in in place) & shine a bright white light steadily onto the cotton holding the light source a meter or so away from the white cotton / front of your scope. You are aiming for the white cotton to be evenly illuminated & the white cotton diffuses the light from the torch so that the optics & your camera see a uniform 'white wall' of light. These flat lights will record the vignetting & the out of focus dust spots as shades of gray & these can be used in the stacking calibration process to even things out a little.

Next is the general noise in the image - I'm guessing you have set the iso quite high 1600?? - you may want to turn this down a bit. In the summer months when its warmer you may want to drop to 400, in the colder nights you might get away with 800.

I've taken the liberty of having a very quick 5 min play with your image. More time spent on it would do it justice, but you can make some big steps in a short space of time.

I ran GradientxTerminator first, which others have recommended here - this deals with the uneven illumination. I drew a selection circle around the nebula & inverted the selection, then did 3 runs of GradientxTerminator at course, medium & fine with the medium aggressive setting.

Next I used Curves tool in Photoshop to tweak the background sky colour - I dropped the red & green a little relative to the blue as this gives a more pleasing inky blue black to the background sky. I put a eyedropper sample point in an area with no star of nebula (yours read around 35,35,35 for RGB), I then pulled up curves, selected the Red channel & used the 'finger' icon & clicked on the image at the eyedropper sample point - this put a dot on the curve line & I dragged it down until the red figure dropped to 25. I did the same for green. Normally I'd spend more time 'balancing' the rest of the image up - but this was a 'quickie'

Next up was to quickly deal with some of the noise. I used noise Ninja & booster the chromience sliders (too much - but this exaggerated teh effect for you to see).

If I spent more time & was careful, I could get it looking more natural, but I really wanted to give you a quick idea of how each of the above issues can be dealt with- - I hope it helps.

[steppenwolf]

This is an excellent start but I can't add any more to what has already be said about darks, flats and more subs!

[RikM]

There is no set number for how many subs to take. More is better up to a point. With my DSLR I try to take at least 30 but my best images were all using 60 - 70 lights. I normally used about 30 darks, 50 flats and 90 bias. Flats and bias are so quick that you can take loads.

LDUNN1 has explained flats nicely. What I tend to do is set the camera to AV and take a couple, then look on the screen to see what exposure time the camera used. Then I dial this value in in manual mode. This makes sure they are all the same exposure time. It seems to help with the stacking.

Bias are frames taken like darks, with the dust cap on, but at the shortest exposure you can. Mine are 1/4000sec. They deal with the readout noise of the camera sensor. If you just use lights and darks you don't need them, because the bias is included in the darks already but if you take flats, you need the separate bias frames for deep sky stacker to apply to the flats before stacking. Other stacking software does it differently though.

In DSS you can just load all the frames by clicking on the right name (don't worry about flat-darks or dark flats, can't remember which term is used). Make sure all the different frame types are using the same ISO.

If you want more info, get a copy of 'making every photon count' by Steve Richards (SGL's very own Steppenwolf). This is a great book and will point you in the right direction.

EDIT: must learn to type faster