Narrow-band solar imaging is both
challenging and rewarding. Looking through one of these marvels is
amazing but, taking a picture to show others is beyond cool.
Many (like myself) start with the
family camera and then, after a little success, move on to dedicated
astronomical instruments. Either way it will come down to try and
try again. No matter which way you choose to share the sun, remember my
motto - it's a hobby, keep it fun!
Imaging
CCD
The
main advantage of astronomical CCD cameras is that they offer the
ability to image the entire disk of the sun with just one shot. Large
chip sizes are available and high dynamic range allow you to capture
both disk detail and prominences with one click.
After adjusting for focus, I usually take
(called "grab") around 10 monochromatic images with the SBIG ST-2000 at shutter speeds between .001 and
.040 seconds without a neutral density filter or at .04 and .08 with one.
I save as a .fits file. Pick the one that has the sharpest focus
and open it in PhotoShop.
Video
Despite
the small chip sizes, video and webcams offer you the ability to capture
many frames over a short period of time and stack them together to
reduce the effects of the atmosphere. Real time viewing is a major plus.
You simply align the feature of the sun you're interested in and click
the capture button. Once saved, RegiStax will align, stack and sharpen
your image for you. Next stop PhotoShop.
Processing
the sun in Adobe PhotoShop
For the disk, I’ll first
process it with Filter | Sharpen | Unsharp Mask and get it as clear as
possible without causing artifacts to appear. The radius is set to 1.0 pixel and the
threshold to zero. It's pretty simple, open Unsharp Mask and move the
slider.
Next, under Image |
Adjustments | Levels, I’ll adjust the mid-tone point slider to darken
the disk detail and then the white point slider to brighten any active
regions. Don’t worry about the prominences at this point.
Once you’ve got
it where you like it, use the wand tool (press W) to select the disk and
copy the image. Click directly on the edge (limb) of the Sun. Right
mouse click on the Sun and click Select Inverse. Next select Edit | Copy. I usually set the wand
tolerance (at the top of the page) to 10 to capture as much of the limb
as possible. It also helps click Select | feather and feather the
highlighted disk. Set the feather radius to 1.0 pixel.
I’ll open another copy of
the raw image and process the prominences the same way. You’ll probably
only use the white level slider. The disk will be
completely overexposed but it makes no difference. Get them as sharp and
bright as possible.
Edit | Paste the processed disk
image onto the processed prominence (or as another layer) and align them with the
move tool (V) and keyboard
arrows or further with Edit | Free Transform. Select Layer | Flatten
image and save.
Colorizing
For the color, I switch to
Image | Mode | RGB color mode and open the Image | Adjustments | Curves
function. Use the drop down list and adjust each channel individually.
Click and drag the Red channel up and left, Green down and right. Blue
down and far right. You’ll have to experiment with the settings to find
a color you like but that’s half the fun!
You can also go back and play
with the Image | Adjustments | Hue and Saturation or Image | Adjustments
| Color Balance and try different settings.
Comparison for Solar Imaging
CCD Pros
Large chip sizes for whole disk
Fast shutter speeds
Small pixel sizes (more details)
Cons
Expensive
Webcam Pros
Inexpensive
real time viewing (wysiwyg)
Excellent for individual features
Cons
Small chip size
Test Images
Here are three raw solar
images to test your processing skills. Each one is a 1Mb TIFF. Right
mouse click on the image and select "Save Target As". Have fun!
Get a copy of Adobe PhotoShop
CS2 here (320 MB download):
The
main advantage of astronomical CCD cameras is that they offer the
ability to image the entire disk of the sun with just one shot. Large
chip sizes are available and high dynamic range allow you to capture
both disk detail and prominences with one click. 
