Below are sample histograms using the DMK 41 camera and IC Capture software. They give an idea of the sort of histograms I am aiming for when imaging various solar phenomena in Hydrogen Alpha
Full Disk with Lunt 100/Coronado 90 .5A (Doublestacked)
Ha Solar Full Disk Image Capture
Although I never seem to do any two images exactly the same way, I will attempt to describe at least my general approach to full disk solar imaging in Ha. Things are a bit different for higher res "close-ups" but I will leave that for another time.
I image full disks with my DMK 41 USB camera. To achieve a full disk without having to resort to mosaics I use an Antares .5x reducer, threaded to the DMK's nosepiece. The nosepiece I use is about .25" shorter than the stock nosepiece that came with the camera, and this allows me to just fit the full disk onto the camera's chip. The fit is tighter along the "N-S"axis than it is along the "E-W" axis which is advantageous for my setup for reasons I will give below. To achieve focus with the reducer with both my Lunt 100 with feather touch focuser and Coronado 90 with a Moonlite focuser I require a 2" long as well as a 1.5" long 2" diameter extension. In the case of the Coronado 90 the BF30 straight thru blocking filter is placed at the end of the two extension and the camera with reducer is inserted into the blocking filter. The Lunt has an internal 34mm blocking filter mounted into the feather touch focuser, so the camera with reducer is inserted directly after the two extensions. For the most part I use the Lunt for my full disk shots as it is also the base instrument I use for double-stacking in the "Luntanado" mode for imaging at .5A.
It is important to have close (not exact) polar alignment. I typically capture 2 or 3 minutes of Avi's at a time so I image from a "semi-permanent" mount that is fairly well polar aligned. It allows me to capture the avi's with the full disk or region of interest staying fairly stationary on the camera's chip. It is also important to have enough shade available for your computer screen. I image from a skyshed POD with a rotating dome. I also have a lightweight scope cover that is silver on the outside and dark blue on the inside that I wear over my head and shoulders as needed to cut any glare. The quality of the image is going to be directly related to your ability to see the screen and adjust your settings based on what's really there, and not have the results affected by glare or some other factor that made the viewing of the live screen uncomfortable or inaccurate.
I use the Image Capture software that came with my DMK camera for capturing my avi's. I have found it simple and reliable. For full disk Avi's I choose to always keep the gain setting at its lowest. The exposure setting and gamma settings are in some combination that I set while watching the on screen image such that I can see maximum disk detail and while trying to keep flaring active regions from over exposing. Sometimes this is possible, sometimes not. My settings are determined at "game-time" according to the conditions on the sun. The full disk gamma settings for single etalon Avi's might be 45-65, and for double stack images they might be 85-110. I generally will see some proms when double stacked but I adjust my settings for maximum detail and contrast on the disk. Any proms that are recorded are icing on the cake. If I want to capture maximum prom activity I will capture a separate avi and combine it with the full disk avi in the post processing stage. Higher Res gamma settings are generally lower (40-50 range).
Once I have decided on my settings for the avi I do one last bit of focusing at 250-300x on the screen, focusing in on an active region and using the 10 to 1 focus knob to eyeball what I think is best focus.
One thing I do before the capture begins is I evaluate how evenly illuminated the solar disk is on my screen. For my Single etalon Lunt 100 shots it's always very evenly illuminated when the solar disk is positioned dead center on the camera's chip. When doublestacked however I have found that the lower right of the solar disk is a bit darker so if if I position the solar disk more to the "left" on the chip (along the "E-W" axis I get a more evenly illuminated disk. Having more "E-W" space on the chip helps. I have tried "clocking" the external filter but the darkening is still an issue. During post processing I can always paste the image into the center of a new canvas so it is once again aesthetically pleasing.
Finally I start the avi. For full disk shots I typically take between 1700-2200 frames.
After gathering all my Avi's for the session I save them on a portable drive and then import them onto my main home office computer. I import the full disk avi into Avistack 2.0. For the most part I use all the settings on full automatic with a couple of exceptions. I manually choose what percentage of the best frames for the program to use. Generally speaking, I have it use the best 180-200 frames from a typical 2000 frame avi. I save the final result as a fits file without using any of avistack's wavelets.
I next import the fits file into Registax 5 and use the wavelets function. I find wavelets easier to use in Registax than in Avistack as far as getting the results I like personally.
In wavelets I use Level 2 and Level 6 only. The setting vary but they are generally close to the same setting for each, around 10-20, depending on the individual image. I then save the final result again as a fits file.
Finally, I import the fits file into Photoshop CS2. For the most part all my full disk images get some treatment with levels, contrast adjustment, and curves. I like to adjust the midpoint in levels to ensure that the limb darkening of the solar disk is preserved and slightly enhanced to present a more spherical 3D look to the sun. Just my personal preference. Many solar images out there today have a flattened "pancake look" and I try to avoid that. I save the result as a jpg for my website and then create a color version as well. For color I will use the levels function, reduce the blue channel to zero, cut the green channel by about half and adjust the red channel slightly to taste. I would then use the color adjustment and saturation features to adjust to taste a bit more. I do not try to achieve exactly the same color every time---each image is to taste.
Prominances (full disk) with Lunt 100 THa single etalon
Active region using a 2.5x TeleVue Powermate and the LS 100THa
Processing AVI's with Avistack 2.0
(AVI stacking and aligning process - settings and a sample workflow)
I use Avistack 2.0 for processing my solar imaging avi's. I have found it gives me good of control over what frames I use. It is very flexible and fast. I currently run it on a Windows 7 64 bit machine.
Its important to set a few parameters first, before beginning your processing.
First go to settings at top of screen>update display>choose "none". This will speed processing time up immensely.
On the parameters and settings "tree" at the right of screen:
Click on the + by frame selection
Under frame selection change from automatic to manual (just click on the word automatic and it will change to manual)
Leave frame alignment at automatic
Area radius to 128
Search radius to 64
Use flat/dark no
Make sure it says "continue processing" under "frame aligned movie"
Leave ROI selection automatic
Leave set reference points automatic
Leave quality analysis automatic
I have noise reduction at 1
Quality size area 84
Make sure it says continue processing under quality diagram
Make sure it says continue processing under quality sorted movie
Reference point alignment automatic
Area radius 24
Search radius 1
Make sure it says continue processing under reference point alignment diagram
Frame stacking automatic
Saved stacked image automatic
File type fits or tiff ( your choice)
Bit depth 32
Post processing manual
Here you can choose which post processin tools you want it to show you. I don't use any of these in avi stack. I do all in photoshop cs2. If I use wavelets I prefer registax wavelets.
Save processed image manual
Extract minimum area
File type I use fits
Bit depth 32
File: I use _pp so I know it's a pre-processes version
Directory. Pick a path to save your processed files in
Save parameters yes
Anything I didn't change remains at default but you can play with those parameters as you get more comfortable. There is probably some setting I need to change but haven't due to ignorance lol.
Ok so once the parameters are ready set you are ready to go. Here is what I do:
Open an avi. Then hit the "process" button on bottom left of the screen. It doesn't really process the file it just reads it by detecting the frames. When it finishes you will see a pic open up and a movie player slider at top right. You can slide it back and forth to see your avi frame by frame.
You should also see a frame selection dialog open. Don't worry about the settings quite yet. Just hit the "calculate" button. It will calculate and rank the quality of eac frame. On my computer it takes about 48 seconds on a 1000 frame avi..
When it finishes you will see a list of your frames in a vertical volume with either a green checkmark or a red x by each frame number. If you left click on a frame number you will see that frame in the picture. If it's been red x'ed it will also have an x through the picture. This means that under the current settings it won't be used in your stack. Ok, what I do next is decide what percentage of all the frames do I want it to use. I generally use a quality cut off of around 5% on full disk shots and maybe 3-5% on closeups. On prom closeups I might go as high as 10%. The nice thing about avistack is you can change this based on your seeing, and overall quality of the raw shots. I look at some of the green checked ones and if I think they are still bad I lower the quality cut off percent to use fewer but better quality frames.
I leave brightness cut-off at 0 but have used it in some special cases).. I leave the frame cut off box unchecked.
Now for full disks I usually shoot 1700-2200 frames so a 5% cutoff will leave me from 85 to 110 frames to stack. I rarely make a selection that leaves me less than 50 or 60. On close up shots with the powermate I shoot 2500-3500 frames. I usually try to stack 125-180 frames, but many times I stick wtih 60-70, or in that range. There's no hard and fast rule so play with it.
Remember that after you select your quality cut off on the slider you must hit the apply button so the settings change is accepted. If you look at the parameters and settings tree you will see under the frame selection section a line that says active frames. That tells you how many frames you have selected. Each time you change the quality cut off slider and click apply it will update.
After you decide on the number of frames you want hit "ok" at the top of the frame selection box. It should then continue the processing and stacking under auto mode. Your work is almost done :)
At the end of the processing you should see a final stacked image. Click ok in the post processing workflow dialogue box that opened and a save processed image dialogue will open.
Here you can choose the output file type, add any suffix to the file name and you can choose or change the output directory to save the file in..
Then click save.
I then open the stacked image in registax for wavelets then to photoshop for the rest of any processing. I use wavelets on my full disk images but on my closeups with the powermate I use iterative unsharpmasking for most of my sharpening.
I hope I didn't mess any of this up lol. Just let me know if I can help with any follow-up questions---you can email me at email@example.com
The frame selection phase really is key and gives you much more control over what frames you use without having to select them one by one. Of course you could do that if you wanted..but too much work for me lol.
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