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Old 02-10-2010, 12:05 PM
dpastern (Dave Pastern)
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Basic question on multi sub processing

I've started using lightbuckets just to dip my feet into the astro imaging waters a bit more, starting out with an easy target, M42. I've done (so far):

L x 6 @ 120 seconds (1:1 bin)
R x 4 @ 120 seconds (2:2 bin)
G x 4 @ 120 seconds (2:2 bin)
B x 4 @ 120 seconds (2:2 bin)

The core is (as expected) blown with these images. I'm currently waiting on the scope being available to get some 6 second subs for the core, including some H alpha ones. Flats, bias and dark frames have all been provided too. I've got 2 sets of files to download - calibrated (where flats etc have already been applied), and RAW. I've d/l both sets, but I am using the calibrated shots.

Now - let me see if I'm working this all out right.

1) use deepskystacker to stack the subs for each type - should I output as .fits (not sure if it's available, should look)

2) digital development in Maxim DL 5 for each sub type (or use the stretch command?)

3) bring each sub type into photoshop for curves/levels

4) combine lrgb in photoshop and the rest of PP

Now, since I have Maxim DL5, I can stack in that (rather than deepskystacker), would you say that that is preferred? I've got Donald Waits DVD tutorial (slowly going through it), but so far, it hasn't really mentioned anything pre photoshop, it's all what to do when you've got it in photoshop.

I bought Maxim DL 5 with the user guide, so probably should read through that a bit more, but we all know what user guides for software are like (boring reads, generally little real world usage information).

references to good sites with tutorials on maxim dl 5 appreciated, or books, or both.

cheers,

Dave
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Old 02-10-2010, 02:11 PM
ericwbenson (Eric)
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Hi Dave,
Read the MaxIm help files, really, it won't take more than an hour to go over once., specifically:

http://www.cyanogen.com/help/maximdl...ing_Images.htm
http://www.cyanogen.com/help/maximdl...OC_COMBINE.htm

these online links provide exactly what is in the printed manual and the built-in help file, BTW click on the "Show" link to bring up the table of contents. Then try it with your images. If in doubt leave the default settings. Once your image is stacked, then stretch (Stretch dialog for gamma/log/linear or DDP dialog).

EB
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Old 11-10-2010, 09:03 AM
dpastern (Dave Pastern)
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Update: I'm having no luck at all, I just can't get things to work as I want them. I had a look at the help pages, they're uber technical and of no help to a newbie (typical of software help pages I might add).

I was able to stack the LRGB images OK (I think), but from there I'm getting lost. I used the digital development filter (tried the settings that Donald Waid recommends in his DVD tutorials), the result doesn't look great. From there I've adjusted the screen stretch, which looks more like I want, but the Black is clipped on the exported tiff file and no matter how low I go with the background (I went as low as 100 when using the digital development filter) it clips. I can see the Black is clipping the the screen stretch window before I even make any adjustments.

The image looks good enough exported as is, but I've always read not to clip things. Hence trying to be a good boy and avoid it.

I've also noticed that sometimes, the exported tiff is just a mess of white all over the image, like the stretch hasn't worked properly. I can't regularly repeat it, even when following the exact same steps.

Getting very frustrated. I'm an experienced photographer, and I'm quite competent in Photoshop, but processing astro images is completely alien and illogical imho.

Dave
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Old 11-10-2010, 12:12 PM
dpastern (Dave Pastern)
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Just to show what I mean:

http://www.ecn.net.au/%7Edpastern/images/maxim.jpg

Is it normal for the screen stretch window to look like that? Should I be even playing with it at all? I've read some tutorials that say you should, and others that say you shouldn't.

Any suggestions? I can make the combined LRGB stacked fit file available for download if you need to check it out in more detail.

Dave
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Old 11-10-2010, 04:02 PM
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OzRob (Rob)
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Quote:
Originally Posted by dpastern View Post
Just to show what I mean:



Is it normal for the screen stretch window to look like that? Should I be even playing with it at all? I've read some tutorials that say you should, and others that say you shouldn't.

Any suggestions? I can make the combined LRGB stacked fit file available for download if you need to check it out in more detail.

Dave
You need to remember that the screen stretch is only for the display of the image on your screen. Changing it does not change your data. If you want to see what your data looks like at any point manually change the minimum to 0 and the maximum to 65536 and hit update.

How the screen stretch works is that it makes anything below the minimum black and above the maximum white. It is a good tool to see how much detail is in your data.
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Old 11-10-2010, 07:24 PM
dpastern (Dave Pastern)
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Now I'm confused cos I used the screen stretch, and it looked better on screen, so I saved as tif and the tif now looks like the screen stretched version in maxim. Isn't that then changing the data?

Or should I have taken the non screen stretched version into Photoshop and worked that with levels, curves, etc?

Here's how the same data looks in maxim when I've done the screen stretch:

http://www.ecn.net.au/~dpastern/images/maxim1.jpg

I then did the save as ==> tif and when I open this tif in Photoshop, it looks like the screen stretch. See how though, in the screen stretch, it's clipped at both the min and max values? No matter what I tried, I couldn't avoid that (when using digital development filter).

Dave

edit: i've just done the stacking and digital development filter again and it now is completely different, shouldn't I be getting the same results if I'm using the same settings for both the stack and digital development filter?
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Old 20-10-2010, 03:14 PM
astrospotter (Mark)
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Stretch and high dynamic range fight each other

M42 is a begger due to it's extreme dynamic range. To get the really fine details you may have to experiment to get your stars really tight before you will see tons of detail in the nebula. M42 is extremely hot to extremely dim way out. Your histogram shows lots of pixels way to the right as you have mentioned you expect due to the 120 second exposures. For high range of intensities you may want to think seriously about something that is a bit complicated but works well, HDR combination at a close to final set of pre-final combined images.

You may wish to consider forming your close to final image using 120 sec exposures (or even more if you want real wispy stuff) then one at 20 sec and then one at 5 second exposures or whatever it takes so that trapezium is still a minimum of the 4 stars all showing (so you may need 3 sec, depends on aperture and focal ratio). I'll be trying that sometime in M42 season as it gets way up high (here in the north +35 DEC area).

After you get each one looking ok for the range of intensity that it is meant to cover then use a high dynamic range multi-exposure tool such as the fairly low cost Photomatrix Pro and your goal is to get a non-burned out center so you have to play with settings of Photomatrix.

You can see a B/W image of this sort of technique on this shot I took a few months back and see the very stretched to the very bright 'sort of ok' I am only learning but this gives you an idea.

http://astrospotter.zenfolio.com/p66...410a4#hd5410a4

Factor this in with the experts on this board as they are WAY WAY ahead of my curve as I am fairly new to this 'art/science' of astrophotograply.

Cheers,
Marko
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Old 20-10-2010, 03:46 PM
dpastern (Dave Pastern)
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Thanks Marko. This was my final effort (manual combine of shots from 2 different nights) - not perfect, but pretty happy with the result:

http://www.iceinspace.com.au/forum/s...ad.php?t=66913

Dave
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Old 20-10-2010, 08:03 PM
The_Cat (Jeremy)
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Hello Dave,

Yes, as said before the Orion Nebula (M42) can be really hard to get right.

Many many moons ago I experimented using HDR (before it became fashionable !!) onM42 and here is the result of combining 11 exposures using Photomatix (no stacking etc) the 11 exposure times were 1024 sec, 512 sec, 256 sec down to 1 sec and here is the result:


http://lh6.ggpht.com/_nmcM5hLJalE/TL...0/NGC_1976.jpg

What am I saying ? Have a go using HDR.

Jeremy.

Addition:

The camera is a Canon EoS 350D with a 6" refractor.

Last edited by The_Cat; 20-10-2010 at 08:05 PM. Reason: Change the image link and addition
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Old 21-10-2010, 03:50 AM
astrospotter (Mark)
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Very nice result

That link looks fantastic. I guess I read your original question too fast. I think your question was on stretch and misunderstood. Very nice image for that post-processed shot and a real keeper. Certainly better than my current efforts by a long shot.

Thanks for sharing,
Marko
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Old 21-10-2010, 01:03 PM
dpastern (Dave Pastern)
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Thanks Jeremy - I do need to get Photomatix one day, HDR is something I want to do some more of.

Marko - thanks for the comment! I'm a total newbie to imaging and processing, so I'm *sure* other experienced users could do even better than my effort.

Dave
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Old 30-10-2010, 03:38 PM
dpastern (Dave Pastern)
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Update: have purchased Photomatix, since the dollar is so strong. Haven't done anything with the image though (yet).

Dave
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