The more I do this astrophotography thing, the worse I seem to get.
I've collected about 30 minutes of subs of M42 with about 20 darks and 50 bias. Most of the subs are taken at ISO 1600 and 30 seconds, with about 1/3 at iso 400 and 30 secs, and 5 at iso 1600 and 90 secs.
Ive posted screen shots of the stacked files, tweaking of the RGB, then luminance & the saturation (histogram and settings included), and you can see the appalling results before your eyes. Firstly, there is an obvious stacking artefact - linear bands across the stacked photo which I assume is the different camera frame angles at the time of image acquisition. Then its impossible to get the blue and red without a green cast across the whole image.
Ive included a single sub (Iso 1600, 30 secs) which looks much better without doing any stacking or processing.
Should I have stacked the subs at ISO 1600 separately from the other ISO subs? How to I improve the colour balance?
Should I just give up and go back to visual only?
The images look fine to me Luke.
I don't do any fiddling in DSS simply stack and save the final TIFF file and then tweak in in Photoshop. 30 mins should give you a fair amount of data to play with.
There are quite a few on line videos on how to process M42.
Keep up the good work.
Bo
DSS has 3 options for stacking: "standard", "mosaic" and "intersection". If you want to get rid of the stuff that's not overlapped by everything, change it to "intersection".
You'll just have to crop out the other stuff in Photoshop first, then do your stretching and colour correction.
Hi Luke, Why is the single frame orientated differently from the other
examples? In the third example I see the luminance sliders are all over the place. The upper slider of each pair should remain on zero. The lower slider of each pair should not end up far from the default settings. Only relatively minor adjustments should be needed. The top slider can be increased from it's default 80 to maybe 90 if you want to darken the background a little. The middle one can be moved a little from it's default
33 if you want to show a bit more or less nebulosity. The bottom one
can be reduced from it's default 50 if you want to quieten down the bright core of M 42 a bit. The straight diagonal line from bottom left to top right
should be a curve when the stacking is complete. The RGB dotted lines
should intersect with the aforementioned curve around a fifth to a quarter of the way up the histogram. Try that for a start.
raymo
The images look fine to me Luke.
I don't do any fiddling in DSS simply stack and save the final TIFF file and then tweak in in Photoshop. 30 mins should give you a fair amount of data to play with.
There are quite a few on line videos on how to process M42.
Keep up the good work.
Bo
Hi Bo,
Thanks for the encouragement. I haven't got photoshop but I can try the GIMP software - it looks extremely complicated with a very unfriendly user interface - but I'll give it a go.
DSS has 3 options for stacking: "standard", "mosaic" and "intersection". If you want to get rid of the stuff that's not overlapped by everything, change it to "intersection".
You'll just have to crop out the other stuff in Photoshop first, then do your stretching and colour correction.
I do use intersection, thats why I'm a little bemused by those linear artefacts. It seems very odd to me. Is it possible that its light from my house, which is 30 metres away from my site? Someone turned a light on during on of the sessions gathering data.
Hi Luke, Why is the single frame orientated differently from the other
examples? In the third example I see the luminance sliders are all over the place. The upper slider of each pair should remain on zero. The lower slider of each pair should not end up far from the default settings. Only relatively minor adjustments should be needed. The top slider can be increased from it's default 80 to maybe 90 if you want to darken the background a little. The middle one can be moved a little from it's default
33 if you want to show a bit more or less nebulosity. The bottom one
can be reduced from it's default 50 if you want to quieten down the bright core of M 42 a bit. The straight diagonal line from bottom left to top right
should be a curve when the stacking is complete. The RGB dotted lines
should intersect with the aforementioned curve around a fifth to a quarter of the way up the histogram. Try that for a start.
raymo
Thanks Raymo - practical advice as usual. I fiddled with the luminance because if I did wild swings and they made little or no difference to the image. Perhaps my expectations are set a little high?
The single frame is oriented differently because I took a lot of the data about 4 weeks ago, and I assume the camera was in a more vertical orientation for those subs.
The diagonal dotted line on the histogram always remains diagonal, with only very slight variation when I adjust the saturation and luminance. I noticed on the youtube clips by Forest Tanaka, his histogram is a sigmoid shape. In every instance that I've stacked, its always linear to start with, then slight bumps appear with the adjustments. As I said, I'm just blundering around in the dark.
Sounds like something is seriously amiss. The line is always a curve when
my laptop finishes stacking. The user manual for DSS [ the help tab at the bottom of the DSS screen] is quite comprehensive; have you read it?
raymo
Sounds like something is seriously amiss. The line is always a curve when
my laptop finishes stacking. The user manual for DSS [ the help tab at the bottom of the DSS screen] is quite comprehensive; have you read it?
raymo
Because I'm using DSS through wine skin (I'm a Mac user) the help menu doesn't work.
I'm beginning to see that macs and astrophotography are not easy companions!
Thanks for the encouragement. I haven't got photoshop but I can try the GIMP software - it looks extremely complicated with a very unfriendly user interface - but I'll give it a go.
Luke
I downloaded GIMP a couple of weeks ago and the learning curve was surprisingly shallow. With the help of google, I was able to find the answers to most of my questions on the programs functions.
The multi-window user interface was confusing at first but quickly learnt.
Ralph
Because I'm using DSS through wine skin (I'm a Mac user) the help menu doesn't work.
I'm beginning to see that macs and astrophotography are not easy companions!
I use a mac for everything in my AP. You'll be surprixed how many of us are out there
Try Nebulosity from stark labs - same crew that releases pHD. Works well, even has some photoshop like functions built in.
Look at Sky Safari for planetarium software as well, it's a very cool app on OSX.
Another Mac user here...Pixelmator is another option that is relatively inexpensive and near-Photoshop functionality.
I can't explain the funny overlapping. What I usually try to do is make sure that when I take multiple sets of subs that the camera orientation is more or less the same. A couple of degrees doesn't matter all that much, as DSS will happily stack em all but the more they don't match the more it crops out in intersection mode.
there may be more tutorials available than other programs anyway its another option for you to consider.
also have you tried stacking without the bias files? I was fairly sure DSLR imaging doesn't require bias frames.
cheers
"Mac running OS X 10.4 through 10.6 with the necessary translator installed."
I'm running mavericks, so this isn't available to me.
I thought bias frames detect hot pixels on the DSLR sensor, and darks are for noise.
I'll give pixellater and nebulosity a go.
Thanks for the tips everyone - hope to make some progress but I'm sure I'll be back for more advice.
I use Nebulosity, StarTools and Aperture for all my processing on my Mac. Nebulosity is great for all your stacking and rough work and Aperture is fantastic for finishing off your images. StarTools has a lot of advanced features and I am only just starting to get the hang of it and using it more and more.
Have fun! I think Nebulosity will be a breath of fresh air after using DSS.
I use Nebulosity, StarTools and Aperture for all my processing on my Mac. Nebulosity is great for all your stacking and rough work and Aperture is fantastic for finishing off your images. StarTools has a lot of advanced features and I am only just starting to get the hang of it and using it more and more.
Have fun! I think Nebulosity will be a breath of fresh air after using DSS.
Cheers
Jo
Thanks Jo. It's reassuring to know there are plenty of Mac users who can do astrophotography successfully, but slightly disconcerting to realise that the problem clearly lies with me. A bad worker always blames their tools, as they say.
Histograms after stacking [1], and after the basic DSS adjustments.[2]
Please ignore the irregular image frame in no.1, my laptop is very short of memory.
raymo
Histograms after stacking [1], and after the basic DSS adjustments.[2]
Please ignore the irregular image frame in no.1, my laptop is very short of memory.
raymo
Thanks for posting that Raymo- intriguing to say The least. So, I have never had that sigmoid shape of the dotted line, it's always a straight diagonal line. It must be either my camera, or the settings on DSS.
I should look at the histograms on the subs on the camera to compare.
Any other suggestions?
