Sky and Telescope - September 2015 - 70

Imaging Technique

present. But as noted earlier, the target comet will trail in
exposures longer than a minute or two. The solution is
to shoot lots of short exposures that you'll later combine
in two diﬀerent ways: one registered and stacked on the
comet, the other aligned and stacked on the background
stars. Stacking many short exposures has the beneﬁt
of producing a deep image with signal comparable to a
single long one.
The technique described below works on any DSLR or
CCD images. (As with any deep-sky imaging, make sure
to calibrate all your ﬁles before moving on to stacking.)
To register your photos in ImagesPlus, select Image Set
Operations > Align Files > Align Files - Translate, Scale,
Rotate. This action ﬁrst requires you to select the images
you wish to combine. Navigate to the folder containing
the ﬁles, and then hold down your control key and click
on all the images you want to align, and press the Open
button. Next, the Align TSR window opens, where you'll
select a few options. Under Feature Selection Type,
choose On Each Image, then select Translate Only under
the Alignment Type section. Next, select the Common
Point or Star and Reference Image in the Alignment
Feature Selection area.
With all these settings chosen, move your cursor over to the ﬁrst image displayed and click on the
comet nucleus; the next image in the set automatically
appears. Select the comet in each of your images until
you're through the set. Once completed, the Align button becomes active at the bottom-right of the window;
click it, and in a few moments all of your images will be
aligned on the comet. Click the Done button.
Now let's align the images on the background stars.
70

September 2015 sky & telescope

REMOVING STARS After stacking exposures in ImagesPlus,
vestiges of the brightest stars might require additional masking
to clean up fully. Use the Special Star/Area Processing option to
isolate the comet's bright head so it won't be erased by the ﬁlter.

Open the same Align Files window as before, but this
time select Translate, Scale, Rotate under the Alignment
Type section, and Common Angle Deﬁning Point or Star
in the Alignment Feature Selection area. This time you'll
need to click on two stars as your alignment points before
the Align button becomes active. Click it, and in a few
moments your second alignment set is complete.

Removing Stars
Once both sets of images have been aligned, you can
stack each set together. Start with the comet-aligned

FLOATING FREE If everything goes as planned, at this stage
you should have a deep comet image with only the faintest hint
of trailed stars in the background.

Sky and Telescope - September 2015

Table of Contents for the Digital Edition of Sky and Telescope - September 2015

Contents
Sky and Telescope - September 2015 - Cover1
Sky and Telescope - September 2015 - Cover2
Sky and Telescope - September 2015 - 1
Sky and Telescope - September 2015 - Contents
Sky and Telescope - September 2015 - 3
Sky and Telescope - September 2015 - A
Sky and Telescope - September 2015 - B
Sky and Telescope - September 2015 - 4
Sky and Telescope - September 2015 - 5
Sky and Telescope - September 2015 - 6
Sky and Telescope - September 2015 - 7
Sky and Telescope - September 2015 - 8
Sky and Telescope - September 2015 - 9
Sky and Telescope - September 2015 - 10
Sky and Telescope - September 2015 - 11
Sky and Telescope - September 2015 - 12
Sky and Telescope - September 2015 - 13
Sky and Telescope - September 2015 - 14
Sky and Telescope - September 2015 - 15
Sky and Telescope - September 2015 - 16
Sky and Telescope - September 2015 - 17
Sky and Telescope - September 2015 - 18
Sky and Telescope - September 2015 - 19
Sky and Telescope - September 2015 - 20
Sky and Telescope - September 2015 - 21
Sky and Telescope - September 2015 - 22
Sky and Telescope - September 2015 - 23
Sky and Telescope - September 2015 - 24
Sky and Telescope - September 2015 - 25
Sky and Telescope - September 2015 - 26
Sky and Telescope - September 2015 - 27
Sky and Telescope - September 2015 - 28
Sky and Telescope - September 2015 - 29
Sky and Telescope - September 2015 - 30
Sky and Telescope - September 2015 - 31
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Sky and Telescope - September 2015 - 33
Sky and Telescope - September 2015 - 34
Sky and Telescope - September 2015 - 35
Sky and Telescope - September 2015 - 36
Sky and Telescope - September 2015 - 37
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Sky and Telescope - September 2015 - 40
Sky and Telescope - September 2015 - 41
Sky and Telescope - September 2015 - 42
Sky and Telescope - September 2015 - 43
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Sky and Telescope - September 2015 - 46
Sky and Telescope - September 2015 - 47
Sky and Telescope - September 2015 - 48
Sky and Telescope - September 2015 - 49
Sky and Telescope - September 2015 - 50
Sky and Telescope - September 2015 - 51
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Sky and Telescope - September 2015 - 53
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Sky and Telescope - September 2015 - 55
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Sky and Telescope - September 2015 - 57
Sky and Telescope - September 2015 - 58
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Sky and Telescope - September 2015 - 60
Sky and Telescope - September 2015 - 61
Sky and Telescope - September 2015 - 62
Sky and Telescope - September 2015 - 63
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Sky and Telescope - September 2015 - 70
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Sky and Telescope - September 2015 - 84
Sky and Telescope - September 2015 - Cover3
Sky and Telescope - September 2015 - Cover4
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