The arrival of my Coronado PST Solar Telescope opened a new field for me, as Imaging and Postprocessing the Sun in Ha is quite different from what I had done so far.
So I experimented and made notes of what I did, and after a while decided to write this Tutorial, so that I would not forget what I learned and also share it with you.
1. Preparation and Prequisites
I assume you already know how to handle your PST for visual observation, that you are able to use the (web)camera and also that you are familiar with my Planetary Post Processing Tutorial.
To capture the image discussed in this Tutorial I used the following equipment:
And I used the following software:
2. Getting the Sun on your screen
This is the easy part: with the finder dot of the PST in the centre you will soon see the Sun on your screen.
Oh: I crawl under a dark bath towel so that I can see the laptop screen [warning: onlookers will enjoy this and make funny remarks].
Just do some coarse focusing [fine focusing comes a bit later] and we are off to the next step.
)
|
Imaging the sun [white light or with PST] is not easy, because it is hard to see the screen of the laptop. Therefore I use a dark blue bath towel and hide under it. While on holidays my wife could not resist the temptation and imaged ... me |
IMPORTANT: you CANNOT reach focus in PRIME FOCUS with a standard webcam such as the Philips ToUcam and the like, unless you do THIS !!
My rehoused Trust WB-5400 webcam focuses nicely with the eyepiece holder + spacer installed: no disassembly required.
However I prefer to use my Televue 2.5x Powermate which gives a better scale IMHO.
3. The actual Imaging
My demonstration image actually exists out of TWO images, which were combined during the post processing (see later).
One image holds the prominences and the other image contains the 'surface' of the Sun.
To reveal the prominences I recommend to start with an overexposure, whereas the filaments and granulation do require a more normal exposure, with the K3CCDTools Brightness Meter at values in the range 175-225.
To actually capture the prominences I recommend the following settings [but you should experiment yourself of course !]:
Now it is time for fine focusing, for which I use what I call "the granulation setting".
To capture the granulation or the filaments you can use the same setting as for the prominence, but with a much shorter exposure: just decrease the expsure time till the granulation nicely shows up and the K3CCDTools Brightness Meter is in the range of 175-225 or whereabouts.)
Habitually I use this 'granulation' setting for fine focusing: use BOTH the focuser and the etalon tuner ring and use the ZOOM function of K3CCDTools.
When you are happy with the focusing go back to the 'prominence settings' and start scanning the rim of the sun for prominences. Once you spot one try to improve the contrast by gently rotation the etalon tuner and/or by tweaking the brightness and gamma/gain settings of the webcam.
Oh: I almost forgot: make sure that you have North UP, which you can easily check by moving the PST up (=North) and down.
When moving the scope to the North the image should go down etc. This way you can can also adjust the East/West orientation of your camera.
With properly oriented images it will be easy to compare your images with those made by others.
Finally at last you are now ready to image; I recommend for prominences to use sequences of 30 seconds at 10 frames per second, as longer sequences will smear the details because prominences rapidly change. Other solar features can be imaged for 60 secs or more.
After imaging the prominence of course you also image the granulation (do not move the scope around during the imaging session !!)
4. Aligning, stacking and wavelets
After imaging it is time for post processing; I use Registax5 and this tutorial and after aligning/stacking/wavelets I have these 2 preliminary results:
Image 1: The prominences
Image 2: The granulation
Note: the above images are shown here as 8-bit jpg files, but in reality they are 16-bit FIT files.
The white borders are a by-product of Registax, where I did the wavelet processing. These borders will be cut off later.
5. Post processing [Photoshop]: colours and mosaic
To process the FIT file[s] I use the Photoshop Plugin FITS Liberator.
I highly recommend this plugin, which is freely downloadable; I also recommend the FITS Liberator Tutorial by Noel Carboni.
I save the output of the FITS Liberator processing as TIFF files, each with the suffix "fitslib", so that later I know that this is the result of the FITS Liberator processing.
Sometimes I wish to colourise my images, however this should be done with care as the finer details might get lost when colourising.
HINT: Save after each intermediate step, so that you can redo later.
The Variations Panel; to colourise I use 3x "More Yellow" and 3x "More Red", but that is something personal of course.
And here is the result of the Granulation image, now colourised:
And via Images|Adjustments|Brightness/Contrast you can use the Contrast slider to get a richer colour, like this:
As we only want the Prominences and not the overexposed Sun we now only select the'sky' part, which we do as follows:
We use the Magic Wand Tool to select the Sun [you can fine tune the selection with the Tolerance]:
and next Invert the selection so that only the 'sky' is selected:
Now you can manipulate just the 'sky' with the prominences; I tweaked a bit with Adjustments|Contrast-Brightness and Curves [Blue Channel] and Levels [Blue Channel] and am rather pleased with the result, but I am still searching for a way to colourize the prominence in a fiery yellow/red colour and the rest of the sky in very dark blue or black.
Via Edit|Copy I copied the 'sky-with-prominences' and pasted this part over the image of the Sun-with-Granulation.
Now use the Move Tool and the Arrow Keys to precisely position the sky over the granulation image, and here is the result:
All you need to do is to flatten this result via Layer|Flatten Image, Crop and save it.
Oh, the frame around the image is explained here.
5a. Post processing [Photoshop]: another colourisation method
The above scenario worked fine for my but recently I started to colourise in another way:
I stitch the b/w parts together as explained above and crop the edges off.
Then I colourise by converting to RGB 8 bits [via Mode] and apply the colours as follows [via Image|Adjustments|Colour Balance or Ctrl-B]:
And as I am lazy I have put the above into a Photoshop Action, which you could do yourself too.
Here is an example of using this colourisation:
6. Post processing [Photoshop]: resulting image in black and white [with a blackened sun]
Should you consider the colourisation too artificial you might prefer this version:
Here is what I did:
I loaded the 'Prominence' image into Photoshop and used the Wand Tool to select the Sun and then used the lower slider in Levels [Crtl-L] to make the Sun black.
Next I inverted the selection [Select|Invert] and used Curves [Crtl-C] to enhance the prominence a bit.
That's all.
7. Post processing: resulting image in negative, which sometimes brings out unexpected details
The following example nicely shows what an image in negative version brings:
){kind=spacer}
|
Filament with Prominences It is especially nice to see the fainter Prominences erupting from the Filament [best seen in the negative version]. September 22, 2009 09:48 UT. Imaging: Coronado PST [on Acuter Merlin Mount] with Televue Powermate 2.5x operating at f/25 [focal length 1000mm] and Philips Vesta SC3a B/W webcam, Baader Infrared Blocking Filter. Mouse in/out to hide/view the negative version. |
8. Measuring the size of a prominence.
With my PST + 2.5 Televue PowerMate + Vesta SC3a camera I once captured the pieces for a mosaic, so then I had the full width of the sun with this setup.
In Irfanview I cropped this solar mosaic 'from rim to rim' so that I had the width in pixels: 1223 pixels for my setup.
The Sun is 109x Earth, so 'one Earth at the Sun' is 1223/109 = 11.2 pixels for my setup.
After having imaged a prominence I measure (by cropping in Irfanview) the size of the prominence in pixels, divide this by 11.2 and I have an idea of the size of the prominence 'in Earthes'.
9. How to image and construct an animation of a prominence.
)
|
Animation of Prominence: approx. 4.8 x 10.3 Earth. [Click the thumbnail to see the full sized version of 700Kb] Please note the balls of fire going up and down. November 12, 2008 11:06 - 11:48 UT. Imaging: Coronado PST piggybacked on LX200 with Televue Powermate 2.5x and Philips Vesta SC3a B/W webcam, Baader Infrared Blocking Filter. |
Here is how I made the above animation:
I used the Interval Timer of K3CCDTools to automatically image during 15 seconds followed by an interval of 45 seconds.
Processing: the 41 AVIs were aligned and stacked + wavelets in Registax [in Auto mode]; the results were saved as TIFFs.
These TIFFs were imported in K3CCDTools and manually aligned using the Show Difference feature;
the results were upsampled 2x, the caption was added using the Text Output Filter and finally saved as GIF.
The final adjustment of the animation was done in Animagic.
10. Using the Trust WB-5400 webcam.
Here is how I use my Trust WB-5400 webcam
){kind=tracking}
|
A Big Blank Sun. March 13, 2009 08:49 UT. Imaging: Coronado PST piggybacked on LX200; prime focus with Trust WB-5400 webcam, no additional filters. |
Camera settings of the above image [as recorded by WcCtrl]:
K3CCDTools setting:
Please note the checkmark for Capture Startup Message box !
This means that K3CCDTools will start the actual imaging only AFTER you hit OK, which gives the WB-5400 time to obey your camera settings, though a bit slow ..
Well worth a visit: Paul Hyndman's Solar Primer.
|
|