I'm new to taking star trails, and fairly new to photography in general.
After my first attempt at taking a star trail, I composited them in Photoshop and when I merged the layers I got this pattern over the image. I'm assuming it's the result of the lens but am unsure, and I have had a hard time defining it which makes searching the internet difficult.
The pictures were taken at the Sunshine Coast in Australia.
I was shooting with a 9-18mm f4-5.6 M.Zuiko lens on an E-P3 body. I was shooting to the south east so I'm getting the curvature from both poles in my trails.
That's not what I'm worried about however. Its the moire like pattern that results from stacking the individual photos.
The photos were taken at 18mm, with a 30sec exposure, an ISO of 4000 and an aperture of f5.6.
I first tweaked the exposure and reduced noise in Adobe Bridge, then imported the photos as layers to Photoshop CS5 where I used the lighten filter on each layer to show the trails.
The moire like pattern only becomes apparent on flattening the image. I tried another series of images that were taken facing south and didn't get the strange effect.
After doing some more reading this morning I realise I should be exposing for at least a minute and use a combo of screen and lighten to get smoother trails but again, it's the weird moire that has got me stumped.