Just a little test to show aperture variation (i.e. inability for camera to move lens to the exact same aperture position in repeated shots) in timelapse photos. To verify that aperture is changing and not exposure time (e.g., that shutter timing is off and EXIF information is incorrect), we use a diffraction pattern test.
This is in regards to a conversation where I posited that not seeing flicker in maximum aperture settings is a poor test, as the camera is as, or more, likely to over-adjust aperture as it is to under-adjust the aperture.
To validate this, we find the highest aperture value that has minimal diffraction on specular highlights, compare it to the next value, then show a cropped section of several shot frames (in this case, 80 frames @ 12 FPS) allowing us to see the variations in diffraction amount. Increased diffraction (higher f/stop, smaller aperture) results in a more star-like shape, and decreased diffraction (lower f/stop, larger aperture) presents a more smooth, blob-like shape.
This video was made with a Pentax K10D and a Sigma 17-70mm lens. The target aperture is f/5.6. ISO is 400, and exposure time is 1s.