Compressed RAW, also known as lossy compression, is a format that reduces the data in a photo.
This will especially effect you in the very-low-signal situation when shooting the night sky.
Tip: Turn OFF Lens Compensation This is especially true when shooting your Darks, Flats, and Biases. Sony claims that Lens compensation isn't baked into their RAW files, but my experience tells a different story. If you're shooing Darks & Biases and seeing weird ring-like artifacts, try shooting with Lens Compensation off.
Example of stacked darks with ring artifact on a Sony Alpha camera.
Tip: Set one the Fn menu item to Interval Shooting It always takes a while to get those first few test shots in place and everything dialed in before you start your interval mode. I keep an item on the Fn menu for toggling Interval Shooting so that I can flip it on without having to menu dive when I'm ready.
Tip: Shoot at base ISO ISO in digital cameras is complicated. Because you can't change the sensor in your camera, you are, in effect, working with a single ISO while shooting. The camera can amplify the signal it receives, but there is no additional data to work with. When you change the ISO, you are telling the camera, "Please multiply the values for each pixel." Now, like I said, it's more complicated than that, but the impact is the same: You are unlikely to get any additional data by shooting beyond your base ISO. Compensate instead via f-stop and exposure time.
Big caveat: the rest of your processing toolchain needs to be sophisticated enough to support this. Experiment with results, because each model is different.
