Around 10 years ago an idea popped into my head on how to do something very different with a startrail shoot. It involved zooming in very slowly during the exposure to achieve a spiral shape in the stars.

I first tried this concept very adjusting the zoom ring by hand in very small increments during an automated startrail shoot. The result didn’t look very good but it was enough to see that with the right equipment I could get something unique.

The only problem was the 'right equipment’ didn’t exist.

Rather than purchase a bunch of bits & pieces online and wait weeks for them to arrive I decided to see what I could come up with using parts I already had around the house.

I ened up using a Vixen Polarie astro tracker as the drive for the zoom ring, a manfrotto tripod attachment that let me mount 2 heads side by side, a role of sticky tape and an empty Milo tin.

Zooming speed is detrmined by the setting of the tracker, I set the Polarie to 1/2 sidereal (half the speed of the stars) this is the slowest setting it has. Further tweaks can be made by changing the size of the tin used as the drive gear. It took a few test shoots to dial this in, I found my results improved as I slowed the zoom rate.

I also found that a couple of hour’s worth of shots looked a lot better than my usual 6-8 hour shoots.

As the machine turns it pulls the tape away from the lens, to get smooth movement you need to make sure the tape isn’t stuck to the lens barrel in that area, a bit of extra tape on the underside of the long piece achieves this.

I was originally planning to build a V2 of this using stepper motor, audrino controller etc but it wasn’t going to fit into my camera bag either way, so I just stuck to using the prototype shown here.

I get some funny looks from other photographers when they see me setting this thing up.

Below is another variation of the machine, this one pulls zoom and focus, the aim was to get a comet like effect on the spiral trails. I didn’t get much testing done on this one, it would take quite a bit of work to get it right, I’d have to run multiple sizes on the drive to tweak the focus independantly of the zoom speed.

I might revisit this concept one day.