SSS can now use temporary files to store work in progress. SSS decides dynamically whether to use files or memory based on the number and size of images, and the available memory. It is now possible to process stacks of 100's of images using as little as 2GB of memory. There is a small performance cost for using files instead of memory. For computers with SSDs, overall processing time is 10 to 20% longer when using temporary files instead of memory.
Changes have been made to the alignment algorithm to improve results for images with one or more of: very high noise, very low noise, very bright sky, very few visible stars in the sky. Typically there will be little or no change in the time required to align images. In the worst case (thing that may not have aligned before) alignment can take up to 3x longer.
The user is now required to type in the focal length of the lens when it is not found in the EXIF information. This can happen when a lens that does not support digital communication with the camera is used. The focal length is used to improve the alignment.
The alignment algorithm now works for a wider range of lens focal lengths.
The user is now required to check a box at the bottom of the open panel if the images are not accurately tracked. For example, if the camera is manually moved every few images to reduce fixed pattern noise in the final result. Most users can ignore this check box. Providing this information improves performance and alignment of images with few visible stars. If this box is not check and the stars are not well tracked the images may fail to align. If this happens, re-open the files being sure to check the box.