Like Rods, Orbs are now fully explained and widely admit to be only unfocused dust illuminated by the camera flash.
There is a huge amount of variety of orbs, including colored, moving, partials, etc... I'll not detailled here how each of them are created, however you'll find thorough explanations here with lots of examples here as well.
The "orb zone"
When an object is too close to a lens to be in focus, it looks fuzzy. However, it becomes fuzzy in a quite specific way. It turns into a series of overlapping circular blobs of light called 'circles of confusion'.
These can appear quite sharp (see top photo) but they are actually a representation of a single tiny point (a highlight) on the complete object (which, overall, then looks fuzzy and out of focus).
You can often see this 'orbing' effect in pictures where there is a portion (particularly in the foreground) that is badly out of focus.
Very small objects, like dust particles or small water droplets, produce just a single circle of confusion (or orb). This effect can occur anywhere but is often only noticed when it occurs at somewhere significant, like a haunted house.
Digital cameras have lenses with a much greater depth of field than film cameras. This means that the nearest point to the camera that is in focus is a lot closer. It also brings the 'just out of focus' area ('orb zone') closer as well.
The 'orb zone' is so close that it is intensely illuminated by the flash. The intensity of the flash increases according to an inverse square law with decreasing distance.
Indeed, if the subject of your photograph is at a distance of 5m, a particle of dust at 5cm from the camera receives approximately 10,000 times greater light intensity!
This creates an 'orb zone' in digital cameras where the light intensity is sufficient to illuminate the faint out-of-focus bits of dust, which appear as circles of confusion (or 'orbs').
The graph shows flash illumination diminishing with distance (to right).
O = too out of focus to be visible even with flash
Z = (orb zone) out of focus but visible due to high flash intensity
B = out of focus but invisible because flash not intense enough
F = in focus and visible
In a film camera, all the zones move further out and the 'orb zone' generally vanishes because there is insufficient flash intensity at the increased distance.
As digital cameras get larger CCDs (not just megapixels but physically), their lenses get decreasing depth of field. This means that the problems of orbs and strange mists should gradually vanish. No more spoiled pictures!
Source
Photos credits
B- Camera tricks
1- Double exposure
To create a ghost effect, place the subject in front of a background that is of average brightness. Take an exposure.
Then move the subject out of the way and expose again, maintaining the registration of the image with that of the first exposure. The will give a ghost-like appearance to the subject because the background is visible through the subject.
Note that this method does not work with dark backgrounds because the second exposure will not be bright enough to be seen through the subject and the subject will look very normal, unless it moves between the two shoots, the result being then to have twice the subject in different posture:
Note that in the above picture, there are two combined results (the woman that appears twice and the blue light streak) of both the double exposure and the camera that moved between the two exposure
edit on 19-5-2012 by elevenaugust because: (no reason given)
edit on
19-5-2012 by elevenaugust because: (no reason given)
sorry,
