Step by step
STEP 1
Using a correctly configured hydrogen-alpha imaging setup, adjust settings to overexpose the chromosphere to white. Gamma should be set to zero or slightly higher (lower contrast). Slew around the Sun’s edge looking for a suitable prominence. Once found, frame your shot to include the prominence and some of the chromospheric surface.
STEP 2
Adjust camera gain setting, monitoring the ‘Peak’ level indicator. Most control programs show this information numerically or with a levels bar. Set the level close to ‘Peak’, but don’t exceed it. Then make your capture. Keep capture times shorter than 30” to avoid motion blur on active prominences; longer times can be used for ones that appear to be fairly static.
STEP 3
Process your capture result in a registration/stacking program such as AutoStakkert! Ensure only the target is selected when setting alignment points (APs) – ie if you use the automatic alignment point option, ensure the threshold doesn’t also select the sky. If you are struggling, switch to manual and do it by hand.
STEP 4
Open the processed image in photo-editing software. Duplicate layer 0 (L0) twice (as L1 and L2). In the upper layer (L2), select the line between the chromosphere and spicule layer, and expand it to cover the prominence. Apply a 4-pixel feather; invert selection (to select over-exposed chromosphere), then delete and deselect.
STEP 5
Select L1 (chromosphere) and using levels, curves, brightness and contrast, adjust to bring out chromospheric detail to taste. Adjust so the interface between L2 and L1 looks fairly natural. If necessary, adjust L2’s levels to improve the join. It may take a few goes at adjusting L1 and L2 to get the composite looking right.
STEP 6
Once happy with the join, duplicate L1 and L2 and flatten them into a single layer (L3), then save the file. To apply RGB colour, select L3 and open the levels tool. Select the R channel and drag the mid-point towards the black point. Then repeat with G and B, dragging both channels’ mid-points towards white instead.