Shooting For Starry Sky Stacker

Starry Sky Stacker is designed to work with images taken with an equatorial mount and that include only sky. There are few other restrictions.

The following advice it written by someone with little experience with deep-sky photography. It might be useful to beginners, but people with experience may wish to ignore what I say (or better, let me know where I am wrong).

Capturing Your Images

Capturing the images is often a lonely and cold job, so dress accordingly. You will need more clothes than you think. Gloves, hats, long underwear, down parka, I have worn them all, in the summer, in sunny California. If you are in rough terrain consider working with a buddy.

Ensure that your camera is set to capture images in RAW mode, not JPEG. Long-exposure noise reduction should be turned off. Long-exposure noise reduction doubles the time it takes to capture the images, which reduces the quality of the alignment and using dark frames (discussed below) with Starry Sky Stacker should produce a better result than the in-camera long-exposure noise reduction. I suggest you set these options on your camera at home where it is warm, comfortable and well lit.

When you get to your location, let your eyes dark-adapt for a good long time so that you can compose and focus. It is difficult to compose and focus on a dark night and you will need your night vision.

Begin by turning off autofocus and then focussing on the brightest object in the sky, trying to reduce it to the smallest point that you can. It is possible to get close to correct focus looking through the viewfinder, but I find that live view mode is essential to get the focus exact. I start by finding a bright star and focus as best I can in live view by trying to make the image of the star small. Then progressively zoom the live view, refocussing at each step. I use a loupe while doing this to get a better view of the display on the back of my camera. Cameras with EVFs have a strong advantage here.

You should use exposure settings that capture the details in objects you want without blowing out too many of the brighter objects. Your exposure times should be chosen so that not too many of your images are ruined due to camera shake caused by wind or other factors. You do not want your exposure times too short, as this means you will be using a higher ISO that makes it more difficult to capture details. The ideal exposure duration depends on your camera, the lens, your equatorial mount, your tripod, the stability of the ground under the tripod, and the wind and other things that are trying to shake your equipment. Experience will be a good guide.

Set up your equatorial mount and aim it according to the manufactures instructions. Then mount and aim your camera at the part of the sky you want to capture.

After you have set your exposure based on your experience, and focused and composed, you want to collect your images with minimal camera shake. The best way to collect the images is to go into live view and use an intervalometer to control the exposures. By shooting in live view, the mirror will be locked up, leaving only the shutter as a source of camera shake. It is important to have autofocus turned off before entering into live view because by default Canon cameras (and maybe others) will continuously autofocus in live view, and since they cannot focus on stars at night, this will mess up the focus you so carefully set. (You can turn off the automatic autofocus in live view but that still leaves open the possibility of accidentally bumping the focus button--something I have done many times on dark, cold and windy nights).

I have no specific advice on the number of images to capture, but more is often better. 50 is probably a minimum. Beyond 200 the gains are small, but might be worth it. You may end up rejecting images because they are not sharp due to camera shake or atmospheric effects. So collecting too many images is a good way to start.

Capturing Dark Frames

With Starry Sky Stacker Version 1.4 and later, you should consider capturing some dark frames. Dark frames can be used to reduce fixed-pattern noise, that is, noise that tends to be consistent from frame to frame, such as hot pixels and glow around the edges of the sensor. To capture dark frames, put the lens cap on and shoot 10 frames with the settings you just used. Do this just before or just after you capture your light frames. Some cameras with really low-noise sensors might be able to save time by only capturing 5 dark frames. If your camera has a particularly noisy sensor, you might want more than 10 dark frames. If your lens cap does not fit tightly, you might have to cover you camera with a dark cloth. It is important to block all light from reaching the sensor.

With versions of Starry Sky Stacker before Version 1.4 I recommend that most users not use dark frames.

Preparing Images for Starry Sky Stacker

Starry Sky Stacker accepts images in many RAW formats and TIFF files. Some reasons on why you might prefer one over the other, and instructions for converting the RAW format images to TIFF are here.