30th April 2011
You know how it is, someone asks you for advice about how to take an unusual type of picture and you have to admit you’ve never tried it yourself.
Well when a good friend asked me about taking star trails with a digital camera I had to admit to being a bit stumped at first.
The problem is that very long exposures at low light levels are somewhat prone to digital noise. The old school film approach was to lock the shutter open for a couple of hours and just see what happens but that was likely to yield poor results with a sensor.
A little research provided the answer of course. A series of 30 second exposures could be combined in Photoshop to create a similar result but with much less noise issues.
The only thing to do was have an experiment.
I set the camera up near to this tree with Polaris centre top of the frame, the rest of the stars should rotate around this point.
The interval timer was set to 31 seconds and the camera at f4 30 seconds iso. 1000. This turned out to be a slight mistake.
Unexpectedly the interval timer waited until the shutter closed to count down for the next shot. Where I had expected just 1 second gap between the pictures I now had 31 seconds which rendered the trails as a series of elongated dots instead of smooth trails.
I lit the tree with a torch in the last frame and then blended the 105 other shots to create the shot you see here.
Not quite what I hoped for but a good learning exercise that ultimately led to the shot I took at Castlerigg in September.