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Dom543

Multispectral StarlightLive Captures Step-by-Step

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Paul Shears, creator of StarlightLive has built a unique feature into current versions of the software that allows to live-stack together color images from frames captured with different filters. This way one can also create color images with monochrome cameras while retaining their inherently higher resolution. Or one can live-synthesize images comprising only the few characteristic narrowband spectra of emission nebulae. Since every filter picks out a part of the light spectrum and several of these spectral components are pieced together, the technique is usually referred to as the multispectral capability of StarlightLive.

The many interesting uses of this technique would merit their own thread. Here I want to show only how to create such an image step-by-step on a very simple example. The purpose is not to demonstrate the full potential of this technique but to give a first hand-on experience for those, who want to try it out. I chose the Dumbbell Nebula M27 because it is bright,large and easily accessible during the entire summer for every amateur from the Northern hemisphere. It also has the advantage that most of its light is emitted in only two two narrow bands of H-alpha and O-III. Hence two filters are sufficient to create a nice colorful image.

Edited by Dom543
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Equipment Needed

 Apart from the usual mount, telescope and camera setup we will also need filters. And most importantly, we will need the capability to quickly change the filters during the live stacking process. To avoid the need for refocusing, the filters should be parfocal. This means that they need to be made of the same type and of same thickness of glass. Typically filters of the same size and from the same manufacturer are parfocal.

To quickly change filters during the stacking process one can use a filter wheel or a filter drawer system. StarlightLive v3.0 and higher can control Starlight Xpress motorized filter wheels from the software. I am not that high tech and use only a manual filter drawer system from Teleskop Service of Germany, than can also be bought fom OPT in the US. Other manual filter drawer systems are also sold by Hutech, Starizona and Gerd Neumann.

The following photo shows one of my setups that consists (from left to right) of a Meade 3.3 reducer, an SCT to T-tread adapter, the TS filter drawer holder (with a drawer halfway pulled out), a T-thread extension, a 1.25" eyepiece holder and a monochrome Lodestar x2 camera.

Reducer+Drawer_assbld.jpg

Another setup that my wife prefers consists of a Vixen flip mirror, the TS filter drawer system, T-threaded extension, eyepiece holder and the Lodestar camera. There is a Meade 6.3 reducer built into the nosepiece of the flip mirror, that is not visible on the photo.

FlipMirror+Drawer_assbld.jpg

For the current exercise I use a Meade 10" SCT on a CGEM mount with the flip mirror assembly of the second photo, Baader 7nm H-alpha and 8.5nm O-III  narrowband filters and a monochrome Lodestar X2 camera. The optical assembly yields an approximately f/4 focal ratio and a resulting focal length of about 1000mm.

Even though I am using a monochrome camera here, everything shown on this thread could also be done with an OSC color camera. The multispectral technique is NOT limited to monochrome cameras.

Edited by Dom543

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General Conditions 

The captures below were made from our attic level deck in the close-in Wallingford neighborhood of Seattle. To the South we have a direct triple view of all the lights of downtown Seattle with all its tall buildings, Space Needle and construction cranes about 2 miles away. One view straight through the air, a second one reflected on the surface of Lake Union that separates us from downtown and a third one reflected through the moisture droplets ever present in the skies of Seattle. So we are bathing in artificial light.

Due to its moisture content, the air here is never very transparent. Even on clear nights we see only the brightest stars with bare eyes. With camera assisted observing, we need longer exposures from here in Seattle than from locations with dryer air.

I am not listing all these hardships to make you feel pity for us. But so that you can properly appreciate the magic of the narrowband filters that help to overcome these handicaps.

O.k. It's time to aim the telescope and launch StarlightLive.

Before we begin the actual capturing, we set the "Display Processing" tab sliders to my favorite baseline values.
- Black Level to 30%
- Contrast to 50%
- All others left at default values.

We also set up the Stacking tab by
- Checking the  "Enable Live Stacking" box,
- Selecting "Mean" mode of stacking.
Below are the tabs from the StarlightLive v.3.0 window with these settings.
1.Proc+Stack_80%.jpg

 

Edited by Dom543

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The Dumbbell Nebula M27 emits most of its light in the O-III and H-alpha spectra. We will use the two corresponding narrowband filters and sythesize our image from these two emission lines.

Step 1: We put in our O-III filter and set the "Exposure Control" tab for capturing the Oxygen emission in the following way.
a.) Set "Exposure" to 30 sec or whatever fits your conditions.
b.) Check the "Green" and "Blue" checkboxes in the "Exposure Channel Mask" area. This is to make the captured Oxygen emission to be displayed in its natural Green+Blue= Cyan color.
c.) Uncheck the "All" checkbox in the "Exposure Channel Mask" area.

2.ExposSet.jpg

Now we hit the Start button. After stacking three frames for nice smooth image, we see the following screen.
4.BG_cap.jpg

 

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Step 2: We switch filters to H-alpha and modify the "Exposure Control" tab settings the following way.
a.) Check the "Red" checkbox in the "Exposure Channel Mask" area. 
b.) Uncheck the "Green" and "Blue" checkboxes.
c.) Keep the "All" checkbox unchecked.
These settings are shown below and they will make H-alpha emissions to be displayed in their natural red.

5.RedSet.jpg

Now we hit the Start button to resume capturing 30 second frames and stacking them on top of the Oxygen frames captured earlier. After adding three H-alpha frames to the stack, we see the following screen.6a.RGB_cap.jpg

We see that the red of the H-alpha has appeared but overall the image we got is somewhat disappointing. Fairly dark, the colors are dull and the red of the H-alpha is overwhelmed by cyan of the much stronger O-III. Had we known that Oxygen is so much stronger in this nebula, we could have taken 15 sec O-III exposures and stacked them together with 30 sec H-alpha frames.

This kind of imbalance of emissions, and hence of colors, is quite common in multispectral work. Establishing the right balance by differing exposure times requires repeated trial and error and spoils the real-time experience. For this reason I show in the next post how to correct the shortcomings of the above image using the selective channel control tools available in StarlightLive.

Edited by Dom543

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Step 3: We adjust display parameters using the sliders of the "Display Processing" tab in the following three steps.

A. We intensify red selectively by the following.
1. Uncheck the "Modify All" checkbox.
2. Select the "Red" radiobutton.
3. Incease Contrast (of red) substantially from its initial 0.50 value.

B. We tone down green and blue slightly to achieve the color balance that we like.
1. Keep the "Modify All" checkbox unchecked.
2. Select the "Blue" radiobutton.
3. Reduce contrast of blue slightly from its initial 0.50 level.
Repeat the same after selecting the "Green" radio button.

C. We liven up the image by making it brighter and more vibrant.
1. Stretch the image by lowering the "White Level" slider. This will make everything brighter.
2. Increase color saturation from its initial 1.00 to 1.50.

The three sets of slider adjustments are shown below.7.Adjust 80%.jpg

Here is the resulting final image.

M27.Dumbbell.Ha.Oiii_2016.6.6_00.28.54.jpg

As one can see, the effects of light pollution are totally eliminated by use of the narrowband filters and we still have natural colors. This is one of the important benefits of this technique for those of us operating from urban locations.

Save the image from the "Image Export" tab, if you are satisfied with it.

Edited by Dom543

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Important Final Note 

Before moving to another object make sure to hit the "Reset" button on the "Display Processing" tab. If you forget to do this, all future captures will be displayed with the skewed color channel balance that we crated in Step 3 to even out the playing field between strong Oxygen and relatively weaker Hydrogen. (It is NOT enough to re-check the "Modify All" checkbox.)

8.Reset_80%.jpg

Finally, I would like to thank to Paul Shears for developing StarlightLive and for incorporating this unique multispectral capability for all of us to enjoy it.

Clear Skies!
--Dom

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Very useful information , and timely as the season of intense astronomical colour is upon us -- always interesting to see the settings others use too.  Lots of experimentation is possible with the multispectral feature. Maybe this could be incorporated into the next version of Don's guide?

Martin

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Mods can we have this thread - "pinned" please so that it stays at the top for quick reference. Pretty Please :-)

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Fantastic guide Dom - the instructions are spot on and should prove immensely useful to people wanting to try the feature out! Nice work :-)

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Thank you very much, Dom. This is a great write-up. I just got an Ultrastar mono camera and am very glad to learn that I'll be able to use it to capture some color images once I obtain a filter wheel. I already have a NB Ha screw on filter. Looks like I should have purchased a filter wheel or drawer with the appropriate filters instead. Oh well, live and learn I guess.

 

Kim

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Great job, Dom.

Martin beat me to it, but I am in process of updating the user guide and would like to include this.  Once I complete the draft, I will send it to you for approval.

Don

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Thank you All!

I hope that this will encourage more users to experiment with and enjoy the real-time multispectral capability of Starlight Live, which is a unique feature not matched by any other software.

Clear Skies!  --Dom

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I thought that some of you might find the following comparison interesting.
After I was done with all the captures and screen shots for the above step-by-step demo, I also took a new capture consisting of only one O-III frame and one H-alpha frame. My original motivation was to be able to provide a comparison for those of you, who are involved in outreach. One possible argument against multispectral captures might be that the general public doesn't have patience for twice as many or three times as many exposures to be stacked as with an OSC camera. Here are the two images copied and pasted side by side.

M27.Dumbbell.Ha.Oiii_2016.6.6_dual.jpg

Left is the 3xOiii+3xHa stack from the first part of the thread and right is the 1xOiii+1xHa quick and dirty version. In my opinion, for purposes of public outreach, the quick version is just as suitable as the original one. When we stack frames captured with different filters, the resulting image still seems to benefit from a similar smoothing effect as when we are stacking frames obtained with the same optical path. At least as long as we are not investigating it with a magnifying glass or try to display it on a wall size monitor.

If we look at the two images closer, we notice that they differ the most, where the signal was the weakest. Several of the "islands" of red near the center of the nebula are missing or are smaller in the 1+1 stack image.This is logical.Stacking makes more difference, where the issue is whether a pixel is hit by one (random) photon or by no photons, than where the question is whether by five or by six photons.

When comparing the two captures, some might even say that the 1+1 image is nicer than its 3+3 counterpart. Due to its nice clean metallic blue-green core, as opposed to the wishy-washy greyish center of the 3+3 stack. What is causing this difference? It is that the weak red signal is missing around the center of the 1+1 stack. Cyan=green+blue. If red is also present, the we have red+green+blue, which is the full spectrum and is displayed as a shade of boring dirty grey. If the red is missing, then we have the beautiful clean cyan. Sometimes half truths are more pleasing than the full truth...

Clear Skies!  --Dom

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Not sure how I missed this post. Dom, many thanks for your commitment to the VA community. I am very much looking forward to experimenting with some gleanings from this guide on my next Dumbbell capture this evening, Blue/Green to OIII and Ha to Red with some of your tweaks in step 3 if needed.

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Hi Brandon,

I like your Hubble palette version of the Dumbbell very much. As S-II is weak, there is no full spectrum and that way it avoids the grayish-white areas discussed in the last paragraph of the post https://stargazerslounge.com/topic/271785-multispectral-starlightlive-captures-step-by-step/?do=findComment&comment=2978458. But more experimentation is always welcome and I am looking forward to your creative implementations of this object.

As for this tutorial thread, I tried to keep things as simple and straightforward as possible. So that first time users can repeat all steps and get comparable results. Or even better ones, if their skies are better, or if they come up with some of their own better tweaks.

Clear Skies!  --Dom

 

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Thanks for the tutorial Dom!  I just picked up a Lodestar X2 and the filters (Ha, OIII, & SII) to try out some multispectral with Starlight Live.  Is it possible to turn off a color channel in the stacked image to see what you're collecting in the other channels?

Edited by Robrj

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Hi Rob. That is always possible, with SLL you will usually be turning off 2 of the 3 RGB channels when doing multi-spectrum.

The control is on the Exposure Control tab, Exposure Channel Mask setting.

Grats on the filters, which did you pick up? Are you using a filter wheel?

 

Edited by Ain Soph Aur
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Hi Rob, If you already have a stack and want to see what the individual color channels contain, then go to the Channel Selection" area on the Display Processing tab and check the rightmost "Display Selected" checkbox. Then only the contents of the one channel will be displayed, whose radio button is checked in the second row of the "Channel Selection" area. It will be displayed in monochrome B&W. This feature can also be used to see what you are currently adding to an already existing stack, provided you are allocating the current capture to a single channel. (This trick is complementary to what Brandon said and for a different situation.)

The ultimate best triple channel NB target for this time of the year is M1, the Crab ( see my avatar also made with a LSx2m).

Clear Skies!  --Dom

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Starlight Live is so awesome. You can grab nice images with little to no experience, and use the built in tools to take your captures to the nest levels.

We have a saying here is the Southern US, "the best thing since sliced bread"

Aka Starlight Live ;)

Edited by Ain Soph Aur
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5 hours ago, Ain Soph Aur said:

Hi Rob. That is always possible, with SLL you will usually be turning off 2 of the 3 RGB channels when doing multi-spectrum.

The control is on the Exposure Control tab, Exposure Channel Mask setting.

Grats on the filters, which did you pick up? Are you using a filter wheel?

 

I bought the Orion Extra Narrowband Set (Ha, OIII & SII).  I don't have a filter wheel.  I'll just be doing it manually for now.  I have a newtonian so I don't think a filter wheel will work. 

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Hi Rob

I use a filter wheel with my Newt. Focus is a bit tight if I screw the Lodestar on to the FW directly, so instead I use an adaptor that allows me to slide the sensor as close as I can to the FW and it is now fine, with plenty of focus range, at least for this Newt.

fwheel.png

I started with a manual wheel but bought the 7-position SX wheel over the summer and haven't looked back. Manual is fine but the USB controlled wheel makes it much faster to gather data (and no chance of moving/vibrating the scope). If you do go in this direction I'd choose one with the largest number of filter slots you can as they all have their uses e.g. I use one covered with a piece of flocking (Don's suggestion) which allows me to take darks without getting up. 

Martin

 

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