@agentgonzo;
@Ripley;
Whitebalance, yes. I hadn't given that a thought. I can see what you mean when doing multiple shots, if whitebalance is set to auto. That's going to go on my photo-checklist for startrail shots
* Manual whitebalance when doing multiple shots for stacking/layering. Check.
Yes, I was thinking about how to compose a startrail shot with a static foreground image, such as the one you show with the tree
And my main concern with that is how to avoid getting the static part over-exposed while still allowing enough of the starlight to be captured.
I'm doing some tests at the moment:
Low ISO with long exposure... seems not to be ideal. The stars don't have enough time to imprint much light on the sensor-pixels before having moved to the next pixel, so the trails remain faint and few even after a long exposure, even though the foreground comes out beautifully and with very low noise.
I also found that light-pollution becomes a huge problem during long exposures. It seems light-pollution can be considered in the same way as a low-lit static foreground image.
Higher ISO with shorter exposures (layered in post-editing (startrails.de is amazing at that
))... seemed to make it easier to avoid over-exposing the foreground while still allowing enough light from the stars to come through (I didn't consider whitebalance on my first test of this though, so I'll have to try again)
What I did was a series of 30 second shots where I left the camera in auto-shooting. Basically like shooting video at a frame-rate of 1 frame, 30 seconds long, every 30 second. I had tall trees in the foreground and they got washed out (became blurry) because of their movement in the wind.
And then I layered them in startrails.de (super easy
) and thus only brightened the startrails and not the foreground or light-pollution, giving some really good results.
The only thing I found was that the short moment between each photo-shoot (when my camera saves the recorded image before beginning the next exposure) was just long enough to give visible gaps in the startrails every 30 seconds, making the startrail appear slightly dotted. Not a big problem though, because it was only visible when zooming the picture in to actual resolution (and obviously not a problem with startrails.de, but rather with how my camera can't multitask (shoot a new image while saving the previous at the same time))
I have a Sony A33, so the CHDK is not an option for me. I use a wired shutter-release so I can lock the shutter (it doesn't have an auto-timer or anything)
It seems this camera has very little noise-problems actually
Even amp-noise is something I have a hard time producing with it (the purple glow on the edges of the image that people on photo-forums talk about in relation to long exposures). I was at first concerned with how much worse the photos would be when doing the auto-shooting, since the camera does not shoot and subtract dark-frames when in that mode. I can only get it to shoot dark-frames when using manual shooting. But so far that hasn't turned out to produce much difference in noise though, although I'm sure as the camera gets older and single pixels may start to go bad it could change.
It shoots 12bit raws or 8bit JPEG's. So far I'm doing most shooting in JPEG. And I use Gimp rather than Photoshop
Thanks for your feedback guys