Sky & Telescope - March 2020 - 31

consuming because it can be difﬁcult to ﬁnd precise reference points such as background stars in all the images, particularly the shortest exposures. No software I've tried can
automatically detect stars and align solar-eclipse pictures.
Shooting with your camera on a well polar-aligned tracking
mount makes it much easier to nudge your individual exposures into alignment.

Stacking Brackets
Let's assume your images are all well-tracked and are ready
to stack together. There are several specialized HDR imageprocessing programs for doing the stacking that I've described
in the past (S&T: Apr. 2012, p. 75). But stacking aligned
images is also relatively quick and easy in the current version
of Adobe Photoshop.
Start by opening the program and selecting File > Scripts
> Load Files into Stack from the dropdown menu. The Load
Layers window opens, where you'll click the Browse button
at right and navigate to your ﬁrst bracketed set of exposures.
Select them all (you can stack almost any format image
ﬁles, including RAW camera ﬁles). When you click OK, in a
few moments your images will be layered one atop the other
sequentially in the order you shot them, either shortest to
longest or vice versa. If you don't see the Layers window, open
it using the dropdown menu Window > Layers. Any layer that
needs additional alignment can be moved by selecting the
Move tool, clicking the layer in question, changing the blending mode to Difference, and nudging it into place using the
arrow keys on your keyboard.
To smoothly combine all the layers, you need to change the
Opacity setting of each layer so that they collectively contribute to the ﬁnal visible image sequentially from the bottom
layer to the top. For my stack of seven exposures, I changed
the opacity setting of layers 2 through 7 at the top-right of
the Layers window to 50%, 33%, 25%, 20%, 17%, and 14%,
respectively, leaving the bottom layer set to 100%. This should
produce a smooth image that shows everything from the
Moon's faintly illuminated surface to prominences, extended
coronal streamers, and even some of the brightest ﬁeld stars.
Simply choose Layer > Flatten Image and save the result as
"group 1.tif".
If your goal is a natural-appearing image of totality, a
great result can be had by just tweaking this stacked image
using Adobe Camera Raw (Filter > Camera Raw Filter). This
ﬁlter lets you adjust the color balance, increase the texture

p After importing a group of bracketed exposures into Adobe Photoshop, you change the opacity of each layer to reflect how much that
image will contribute to the final stack based on its position in the stack,
thus ensuring a smooth transition between the individual exposures.

p You can make a "natural"-looking result after
flattening the image layers with the Camera Raw
Filter by maximizing the Texture and Clarity sliders, and increasing the
Shadows. This produces an excellent image that resembles the nakedeye appearance of an eclipse.

and clarity, and also increase the shadow detail until you
start to see some features in the inner corona as well as the
Moon's surface. Setting both the Texture and Clarity sliders to 100 and the Shadows to 50 produces an eye-catching
result that is very close to what the eclipse looks like to the
unaided eye. Adjust the color balance, save the result with
a new ﬁle name (group 1ACR.tif), and you'll have a great
image of the event. But you can do much more with your
bracketed set.

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Sky & Telescope - March 2020

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