As every astro-photographer knows, the apparent star movement in the sky follows concentric circles around the Polar Star. Is is quite easy to grab this effect just orienting our camera to the north and focusing to the sky. The star-trails are formed leaving the shutter open for a long time or just stacking the individual photos in post-production.

By making large exposure photos we can register this nice effect, see below:

Star-trail astrophotography effect with the Polar Star in the center and the rest of the star following a circular pattern

The same concept can be used to make a time-lapse that will show stars spinning around a common star.

Landscape showing the circumpolar astrophotographic effect, showing all the stars turning around the Polar Star

But, what would happen if we could move the zoom ring very slowly during the hole photo session?  Yes, you got it, the stars would move around the polar star not in circles but in spirals or Vortex star trails.

ZenFocus device making a spiral star trails effect

ZenFocus moving zoom ring for 1 hour. Lens used is Canon EF 17-40 f4L

To make these effects we normally have to make multiple several seconds exposures. The hole session can take hours.

With ZenFocus we can automate the zoom (or focus) ring very easily. We just have to define the start and end point, and the duration of the movement.

In the next photo, ZenFocus moved the zoom ring from 40mm to 17mm during 2 hours.

ZenFocus twisted star trail. The Vortex or spiral effect is made slowly turning the Focus ring of a zoom lens.

ZenFocus moves zoom ring (Canon EF 17-40 f4L) for 2 hours

The photos we recorded had an exposure time short enough not to record trails, just dots in the sky. So, to create the trail effect in the time-lapse and to make more evident the twisted movement of the stars that ZenFocus produced, we used the CC Time Blend effect in Adobe After Effects.

Spiral star-trails with ZenFocus

And remember that ZenFocus has the same controller as ZenSlider. We offer a really nice kit where you can find a ZenController, one ZenSlider and a ZenFocus at a really competitive price. Check here or in the image below.

ZenSlider motorized slider and ZenFocus automatic focus puller