BBC Sky at Night Magazine

Step by step

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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.

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