Starting from a punctual object (O1), completely in focus, the light rays, after going through the lens, will pass through the center (O3) of the diaphragm and then through the second lens, ending in the photographic film in a point (F1), completely in focus.
On the other hand, starting from a punctual object (O2), completely out of focus, the light rays, after going through the lens, would converge at the point O4, but some of the light rays will be blocked by the diaphragm. Only part of it will pass through.
This part is, in fact, a cone with thousands of rays of light. Between points O3 and O4 we have what is called the circle of minimum confusion. As only light will pass, out of focus, through the diaphragm, and it blocks part of the light rays, then the physical shape of the diaphram is imprinted to the photographic film.
It occurs when the objective lens is incapable of focusing the outer and axial rays in the same point. Because of the lens curvature, the borders are thinner while the center is thicker. If the lens is hit by parallel rays, they will pass through different thicknesses in the lens, and will therefore form many different focus points.
An objective lens with spherical aberration will form a diffuse image with little contrast in all visual field. We can reduce the problem closing the diaphragm, using only the central region of the lens.
An objective lens is composed of many elements, going from 7 up to 15 lenses, depending on its quality. This is all to eliminate or reduce the aberrations.
In the image below, we can see that a light was cut out of the original photo, to the right. It generated a coma reflection, to the left (notice the symmetry). Around the reflection we also see a good example of spherical aberration, forming a big ring.
This effect is very common on night films seen on the movies or TV, when car headlights are filmed coming towards the camera. It’s also very clear with TV studio light spots.
Out of focus
Something very similar happens with unfocused images. If we have the focus on a person, for instance, and in the background we have one or more lights, those will be out of focus, and reach the camera on that circle of minimum confusion.
This will imprint the image of the diaphragm on the photo. If we have a diaphragm with five parts, as in the example above, then the unfocused images will have that shape: a pentagon. If the diaphragm has six parts, as in the example below, we will have hexagons. And so on.
The same thing happens if you photograph a light source very closely, with the focus set to infinite. IN the example above, the small holes were captured in film as hexagons, as the diaphragm of the camera had six parts. At left, it’s also possible to see a reddish spherical aberration.
In this photo we can see that it’s out of focus, since the hexagons are all parallel to each other. If they were on a curve, they would align toward a common point.
The coma aberration happens when an objective lens is incapable of forming a puncutal oblique image, producing instead an asymmetrical light area. The light rays are reflected by the internal lenses and reach the film.
This aberration is the one most often confused with UFOs. See the example above of a photo that was cropped. In the uncropped photo, there will always be a symmetry of the source and the reflection in relation to the center of the photograph.
It’s always important to analyze the negatives to verify if the photograph wasn’t developed with cropping. See some examples below.
Out of the visual field
Another interesting visual effect mistaken with UFOs occurs when the source of the light lies outside the visual field of the camera, but insed the visual field of the first lens (the outermost lens).
Those are usually taken almost against the Sun. This effect can be avoided by using a shade. See two examples below:
If you read and understood this article, you will probably start to look at UFO photos with a different view. You may also watch TV in a different way, noticing the many squares, pentagons, hexagons and polygons in general that appear all the time, as well as the Coma and spherical aberrations.
— By Claudeir Covo, ufologist and president of the Brazilian National Institute of Aerospatial Phenomena Investigation – INFA
And Paola Lucherini Covo, ufologist and secretary of INFA
Translated with their kind permission
Popularity: 2% [?]Posted in Science,Skepticism,UFO photos,UFOs | No comments