Under The Stars - What The Astrotracer Can Do

Starscapes

With the camera simply resting on a fixed tripod it is possible to track the stars for several minutes with wide angle lenses. This greatly reduces the noise of the final image and makes Milky Way details much more visible.

Without the need of an equatorial mount, it becomes possible to try different locations to get the best view or composition of a scene since no polar alignment is required.

The image on the above shows a 90 s astrotracer exposure on the stars blended with a fixed 180 s exposure foreground shot with a 16 mm lens.

Images produced with the astrotracer have sharp stars but blurry foreground

Images produced while the GPS unit is turned "off" will have sharp foregrounds but stars that appear as trails. Note that without the moon or other lighting sources it is often necessary to expose longer for the foreground than it is for the stars.

In Photoshop Elements 14 the foreground can be selected and copied using the refine edge tool to make the selection of the edge of the foreground easier and more precise.

On the star image, the edge of the foreground can be erased by copying the lower part of the sky over it with the clone stamp tool of PSE 14 before the sharp foreground is pasted in place.

Deep Sky

The astrotracer will also work with longer lenses.  I've had success with 135 and 200 mm lenses for exposure times ranging from 30 to 60 s.  With fast lenses, F4 or faster, it is possible to record many popular deep-sky targets by stacking many shots together.

The image above is a stack of twelve 30 s exposures with a Rokinon 135 mm lens at f/2.0.  DeepSky Stacker is a freeware program that was used to stack the individual images. Final editing was done in Photoshop Elements 14 using Levels adjustments and Topaz Adjust and Clarity plugins.

Blending of two images is often necessary as the action of the astrotacer will make the foreground blurry.

The two images are taken one after the other.  One with the astrotracer function "on" and the other "off" by turning off the GPS.  

© François Quesnel.

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