Rosencratz

Great read. I've been meaning to learn how to stack my photos for a while now. Sadly my last trip out I only remembered to take 1 dark field shot.

So I shouldn't expect much impact from that?

As an aside though I noticed a lot of mention of how long the exposure should be and thought it might be handy to mention a little rule of thumb I picked up from thestartrail.com (Ben Canales).

The rule is that you divide 600 by the focal length of your camera.

So if you're using a 50mm lens you do:

600/50=12s

This only counts for the "effective" focal range though so if you're using a crop sensor camera (like me, if you're using full frame you'd know it) you also need to apply the crop ratio to your calculation. Usually this is about 1.5.

To save time you just adjust the original calculation to:

400/50=8s (because 400 is 600/1.5)

Generally I only ever go out intending to use one lens. (my widest one with biggest aperture) and so I can easily do the equation before I even leave the house.

I'm under the impression that the finer details of the calculation will show that the angle of the camera will also effect the timing some how too but you'll find the above value in seconds to be about right. It works for me. Some times I take a second or two off to be safe though.

It may be common knowledge but it totally streamlined my workflow when I get on site.