One of the questions that is brought up in paranormal circles is, “If this picture is a bug/dust why does it have a tail?” To answer that question I’m going to describe two scientific phenomena that occur in video and in still photography (as they are related).
A while back, I wrote an article on still photography and shutter speed (https://www.facebook.com/…/nationalparanormalsocie…/search/…, shutter speed, and dust Sanfratello). To capture the illusion of motion in photography, we utilize a slow shutter speed (typically between 1s to 1/15 of a second) to capture the illusion of motion by creating “blur”. The waterfall gif (http://en.wikipedia.org/wi…/File:Shutter_speed_waterfall.gif) shows water moving over a small waterfall and indicates the shutter speed used in the lower right hand corner. Notice that as the value gets closer to 1 second (1/800, then 1/200, then 1/30 then ⅓ then 1 from fastest to slowest), you can see fewer individual drops and the water drops appear to become a solid sheet. In fact, the waterfall volume/rate did not change. The light sensor on the camera is simply capturing more more light as it is staying open longer (think about playing peekaboo with a kid and opening and closing your hands fast versus slow, the slower you close them, the more you see).
In your basic camera/phone, “automatic” settings will use a slower shutter speed in low-light situation (so that the camera can capture more light and show more in a dark shot). In the case of our dust orb in motion, if the dust is close to the lens, it will appear to be a larger streak moving across most of the picture. Further from the lens, you will see a shorter line. The following two photos of a purple light were taken in a “haunted” park near Rochester, NY. Both photos were taken by the same person (a member of my team) seconds after each other. What do you think this strange bar of purple light is? I will give you a hint, it is not paranormal.
Now that you have seen how slow shutter speeds can create the illusion of motion on a still photo, let’s examine the science behind video capture and motion. Remember that I said they are related!
Video (film and digital) is created by stringing together a series of still pictures. In the early days of film, filmmakers created film at 24 frames per second. Video games run typically between 30 and 60 frames per second, but why does our brain perceive motion if in fact, all we are seeing are a number of still pictures?
According to Paul Bakaus (Google Developer), there are two reasons why our brain perceives motion from still photos. Persistence of vision is a phenomena where our retina retains part of a visual image (for approximately 40 ms) and reduces our perception of “flicker” between switching stills; however, the Phi Phenomena allows our brain to “fill-in-the-gaps” and perceive stills that capture motion as motion when displayed at a high enough frame rate (Bakaus, 2014).
Observe the following video showing frame rates of 24 fps and 60fps. http://paulbakaus.com/wp-conte…/uploads/2014/…/60vs24fps.mp4 Do you see a difference in motion between these two frame rates? Does the lower frame rate of 24fps appear to have a slight tail?
Would would the effect be if the object in motion was close to the lens? What would the visual effect be if the object was moving faster or slower?
Bakaus, P. (2014, May 21). The Illusion of Motion. Retrieved November 9, 2014, from http://paulbakaus.com/t…/performance/the-illusion-of-motion/
Sanfratello, S. (2014, October 20). Orbs, shutter speed, and dusts. Retrieved November 9, 2014, from https://www.facebook.com/…/nationalparanormalsocie…/search/…, shutter speed, and dust.