Image Processing
Creating a shot of Mercury transiting the Sun.
How to capture both detail and impressive solar glow in one shot using two exposures
Mercury’s Silhouette Against Our Star was created using two different photos of the Sun, captured during the Mercury transit on 9 May 2016. The equipment used was a Hutech-modified Canon 6D and a Vixen ED103S refractor with a Baader solar filter, all of which was mounted on a Losmandy GM8 tracking mount.
Here we explain the technique used for blending the two different exposures in Photoshop to create an image that shows a greater range of details.
First, capture the Sun’s glow with an overexposed image. Then take another image that is properly exposed to capture the details. Shoot in RAW format and, after downloading the images, open them in the Photoshop plug-in Adobe Camera Raw Process the overexposed photo with a warm tone to make it look more natural than the cool tone of the solar filter; do this by raising the temperature, then lowering the tint slightly. Bring out the highlights from the glow surrounding the Sun by raising the highlights, clarity and vibrance.
Create a warm tone for the detailed image as well, making similar adjustments to the ones made to the first image. To accentuate details, lower the exposure, highlights and blacks while raising the shadows, whites, clarity and vibrance. To add sharpening and noise reduction click on the detail settings and raise the sharpening amount along with the masking and luminance (when you’re adjusting the masking you can hold the option/alt key to view progress).
Two become one
Next, from Camera Raw open both images in Photoshop. Zoom in when working on finer details (click view > zoom in); sometimes the closer the better. To save your progress at any point use the Photoshop format to save files with layers: click file > save as > Photoshop > save. Use the overexposed Sun as a background and place the detailed image over it. To do this select the move tool and click the tab
at the top for the detailed image then move it to the left of the screen. This separates the image from the main Photoshop page so you can work with both. Click on the detailed image again then drag and drop it onto the background image. Lower the opacity under the tab for layer adjustments so you can see through the layer then zoom in and align the two Suns. Now with the detailed image (layer one) selected, adjust the layer opacity to blend the images so the details remain but the background is prominent. Go by eye for this stage and use what looks best.
Now select the eraser tool, click the size adjustment at the top and select the soft round pressure opacity brush from the menu. Set the brush size around 500 pixels and the eraser’s opacity and flow settings at 100 per cent then select the airbrush icon. Erase the outer edge of the Sun and the surrounding black by keeping most of the eraser on the black with very little on the Sun’s edge. This reveals the brighter glow from the background layer with a soft fade effect. Get close enough so only a small amount on the Sun’s edge shows through from the brighter layer. Be patient with this step; it will take several tries to get it just right. Now erase the rest of the black background on layer one.
Change the opacity and flow to around 30 per cent and erase the inside edge of the Sun. Place the centre of the eraser on the Sun’s rim, then move slowly and evenly around the edge. When you have it where you like it, hold down shift and click on the background layer to select and highlight both layers. At the top click layer > merge layers.
The last paste
With the image opacity lightened on layer one, Mercury and the sunspots become lighter. To fix this, select the original detailed image and, holding shift, use the lasso tool to circle the planet and sunspots then click edit > copy. Select the file you were working on click edit > paste. Now lower the opacity to see through the pasted layer. Select the move tool and align them onto the area where they belong. Switch the eraser to 100 per cent and erase what you don’t want, then blend it with the opacity layer adjustment. The same copy-and-paste technique is used with the glow around the sides of the Sun where it’s faded, although depending on your type of scope and filter you may not have a fade in the surrounding glow. Merge the layers then crop the image. Click file > save as > Tiff > save.
Do final adjustments for colour and highlights in Lightroom using your judgement for what looks best. See more of SCOTT TULLY’s photography at www.flickr.com/photos/stully