Author Topic: 50mm pics very blotchy  (Read 8444 times)

Offline oetie

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50mm pics very blotchy
« on: 2014 February 05 05:25:15 »
Hi there,

I was wondering if someone could help me with the following: I'm just starting out, both with astrophotography and with PixInsight. I'm experimenting with a 50mm lens with my unmodded EOS450D on an EQ-3 and though the results look very promising, I do tend to get really blotchy images. My most recent attempt was the constellation of Orion. I took lights, darks and flats (my first attempt at flat files, though). I tried several things, like playing with DBE settings, running multiple DBE sessions, colour correction, background neutralisation, but every time I hit the STF "auto" button, the picture turns into a red/green cow.

Here's an example:
http://www.astrobin.com/full/76709/0/

Is there something I can do to prevent this?

Offline NGC7789

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Re: 50mm pics very blotchy
« Reply #1 on: 2014 February 05 05:30:40 »
Actually to me this looks pretty good. These look typical to me for a DSLR (I shoot a modified 50D and started with an old Rebel 300D). You don't mention your exposure times? How many subs and how long are they. Usually the best way to deal with this is to increase total exposure time.

Another option might be to dither although I don't think your mount can do it and I'm not sure if the dither technique matters as such short focal lengths. I don't dither myself (yet) so maybe others can comment on that.

Offline oetie

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Re: 50mm pics very blotchy
« Reply #2 on: 2014 February 05 07:39:07 »
Hi Caroline's Rose, thanks for your reply!  I have 20 lights, 9 darks and 20 flat files. Per sub exposure time is 5 minutes, at least for the darks and lights. I was kind of hoping that would be enough.

I had to look up what dithering is and I'm afraid that my pictures are already slightly misaligned so I guess that means that they are dithered? :)

I guess I will just have to stretch a little bit more carefully than just hitting that auto button.

Offline NGC7789

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Re: 50mm pics very blotchy
« Reply #3 on: 2014 February 05 07:49:13 »
1 hour of integration time may not be enough. I usually go for at least 3 hours. Give that a try.

Yes, a slightly misaligned mount can give you a dither for "free". However, a true dither needs random offset. Depending on what is causing your drift it may not be random and that could lead to the noise becoming streaks making the background look "hairy".

It could also be that your image could benefit from improved post processing. If you have dropbox or something and you would like to upload your files I could take a whack at them. All your files would give the most flexibility but just the final integration without other processing would do too.

I also just noticed you mention darks and flats but not bias. In order to calibrate properly you must include bias frames. Fortunately you can make these easily after the fact because the optical system is not involved and the temp is not that important because the exposure is so short. With no lens on the body and the cap on take 100 or so shots at the shortest exposure the camera can do. Set it to the same ISO as the darks (which should also be the same ISO as the lights and flats!).




Offline Dimitris Platis

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Re: 50mm pics very blotchy
« Reply #4 on: 2014 February 05 08:15:53 »
Its not that bad....its not easy to use a 50mm lens...

Offline NGC7789

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Re: 50mm pics very blotchy
« Reply #5 on: 2014 February 05 08:26:56 »
Dimitris,

Since Oetie is new perhaps you could share some of your workflow. That's just from the astrobin post right? So I'm guessing even better results could be gotten from the real raw data.

Offline oetie

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Re: 50mm pics very blotchy
« Reply #6 on: 2014 February 05 08:31:20 »
Thanks Dimitris for your version! Which steps did you take to get that result?

Here's a link to the integrated file. I'm also uploading the separate files. I am afraid I will only be able to create bias files and re-pre-process them this weekend.

https://www.dropbox.com/s/7g4800pimnmk6dr/light-BINNING_1.fit

Offline Dimitris Platis

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Re: 50mm pics very blotchy
« Reply #7 on: 2014 February 05 08:32:08 »
Sure,
First of all I should point out that if I had the Raw image a lot more could be done...since a jpeg is practically useless but...can be used still to demonstrate some things.
So...what can u do...
1. U can use Morphological Transformation Tool to remove some Chrominance noise with a Luminance mask (inverted)
2. U can use SCNR to remove the awful greenish hue
3. U can use Morphological Transformation Tool (after u make a star mask) to reduce the size of the stars with morphological selection. That alone will increase the nebula bulk enormously.
4. U can u some of Rogelio's technique on multiscale processing (http://www.deepskycolors.com/archivo/2010/05/07/multi-scale-Processing--Revealing-very.html) to reveal more nebular detail
Also u can boost the color with Curves while keeping chrominance low

Offline NGC7789

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Re: 50mm pics very blotchy
« Reply #8 on: 2014 February 05 08:33:41 »
I will try my hand at your fit this evening once the kids are in bed. I'll bet Dimitris will do wonders too.

Offline oetie

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Re: 50mm pics very blotchy
« Reply #9 on: 2014 February 05 09:03:42 »
Here are the source files:

https://www.dropbox.com/s/9flvpy7os28rugo/orionwf.zip

Thanks very much for your help thus far! I'm looking forward to your versions and I will definitely look at the steps Dimitri suggested next weekend.

Offline Dimitris Platis

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Re: 50mm pics very blotchy
« Reply #10 on: 2014 February 05 12:32:40 »
Thats the best I could do for now for the single file you sent....
Unfortunately it need more integration time in order to bring forth all the nebulosity.....damn chrominance.
Thats the reason I switch to a CCD  ;)

Offline NGC7789

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Re: 50mm pics very blotchy
« Reply #11 on: 2014 February 05 14:43:10 »
Oetie, I don't think I can do better than Dimitris's work. I find this a very satisfying wide field image. You can see the Horsehead after all!

As Dimitris has said more integration time is the key. The good news is that more integration time does not cost money (unless you believe time is money).

Keep at it and I'd love to see more of your efforts.

Offline oetie

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Re: 50mm pics very blotchy
« Reply #12 on: 2014 February 05 22:53:52 »
Wow, that looks amazing! I see that you specified the steps in the file name but I'm afraid I don't follow exactly. You split the file into LRGB? And then? Did you execute the next steps with the separate colours and then recombine? And is CurveContrast something you do in Curves Transformation? Does HDR mean HDRComposition or HDRMultiscaleTransform? Whats MSP? And is that all the steps you took or did you also perform other steps such as colour calibration, DBE, etc.?

I believe you get the point :)

And yes, I do love this result already! You can also see traces of Barnards loop and Sharpless 2-264! I will try to shoot more data as soon as the moon is gone and the weather gets better.

Offline Dimitris Platis

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Re: 50mm pics very blotchy
« Reply #13 on: 2014 February 06 02:33:23 »
Actually Chris, the description in the photo in only the steps after LRGB combination. There are a number of steps for RGB construction and Luminance processing.....I will send u the process later today

Offline Dimitris Platis

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Re: 50mm pics very blotchy
« Reply #14 on: 2014 February 06 08:03:00 »
Here it is...
1. To begin with the Light pollution gradient is so enormous that u have a huge problem to start with. And that is due to the enormous field u have there because of the 50mm lens. So thefirst step is to remove the gradient with ABE and DBE (similar to this http://pixinsight.com/forum/index.php?topic=4385.0).
2. Then u can split the image and extract the Luminance to be used later on.
3. U treat the original image with Background Neutralization, Color Calibration and absolutely SCNR.
4. U can treat the Chrominance noise with ATWT at level 1 or ACDNR or TGVDenoise or anything u like.
5. U use MaskedStretch (I still like the script version) and set target 0.1 (100 iterations). Clip just slightly the shadows with HistogramTransformation and repeat 2 more times increasing the target to 0.2 and then 0.3.
6. U could possibly play with colors and a luminance mask but I found the image too noisy to do that and the color looked OK. Sometimes less is more.

Next stage to treat the Luminance.
1. U create a copy of the image and stretch it with HT as far as STF does it. Then u make a star mask from that (Binarize). Also u use the copy as an mask on the Luminance.
2. Use Dynamic PSF and sample 20-40 stars and make sure that they are not Lorentzian or Gaussian.
3. Use Deconvolution and play with the limits to sharpen stars. (U could avoid this step since star sharpening can be achieved in a far easier way)
4. Delete all masks
5. U use MaskedStretch (I still like the script version) and set target 0.1 (100 iterations). Clip just slightly the shadows with HistogramTransformation and repeat 2 more times increasing the target to 0.2 and then 0.3.
6. Use the LHE procedure (http://lightvortexastronomy.blogspot.gr/2013/02/tutorial-nebulae-pixinsight-workflow.html) described here with 256 and 64 kernel as well as the ATWTsharpen procedure.
7. Make a star mask and use convolution or ATWT (delete 3-4 first layers) on star mask to blur stars and apply that on image. Use Morphological Transformation to reduce star size (Morphological Selection). Play a lot to reduce stars a lot but not create artifacts. (http://www.deepskycolors.com/archive/2011/09/08/star-size-reduction-via-Morphological-.html)
8. Then use Multiscale processing (MSP) (http://www.deepskycolors.com/archivo/2010/05/07/multi-scale-Processing--Revealing-very.html)

Luminance is ready. Now u must combine. SO u have a Luminance image and an RGB image.
Extract Lab colors from RGB image and adjust the luminance of RGB with LinearFit to be equal to that of Luminance.
Channel Combination to combine L,a and b into RGB
LRGBCombination with Luminance and RGB
U can play with the contrast with HT and Curves reducing shadows and increasing highlights. Play around.
U can repeat MSP and finally reduce stars again.

Everything with moderation.
Notice that I HAVENT used Noise reduction at all except for chrominance.