I believe it's worth nothing that even if you don't have dust on the lens, dust particles in the air can still refract light leading to highly diffused points of light which are distinctly out of focus (AKA: orbs). And along that line of thought, the ISO rating of the film or ISO setting (for digital cameras), will not eliminate orb-effects because the light source is rarely the camera's flash. Most of the time it's the sun or other intense light source coming not from the direction of the camera, but from an oblique angle to the camera.
As for those suggesting catch-words such as "energy" and "frequency", an important note is that nothing but the physical has ever been confirmed to exist. There is likely very good reason for that.
But words like "energy" and "frequency" describe purely physical traits/conditions. They should not be applied to anything suggested to be other than physical. And if orbs do exist but do so at a frequency other than that apparent to the human eye, then we shouldn't be accidentally capturing them with our standard optical cameras. Standard photographic film contains an emulsion of silver halide crystals because such crystals undergo a chemical change when exposed to visible light.
The electronic sensor of a digital camera utilizes semiconductors specifically designed to conduct electricity when exposed to frequencies of visible light. So a standard camera can be said to be a device which not only detects visible light, but records the distinct patterns and frequencies of that portion of the electromagnetic spectrum. Cameras even contain a special IR filter to filter out the affects of electromagnetic energy below the visible spectrum. So if the camera captured an image, it's because the image is completely visible to the human eye.
We know there are frequencies well above and well below they range of human vision. We see only a small portion of the electromagnetic spectrum. The spectrum is divided into seven sections; Radio, Microwave, Infrared, Visible, Ultraviolet, X-Ray and Gamma.
As one can see by looking at the graph, the visible range (visible to humans), forms only a tiny part of the full spectrum. But that doesn't mean that we are unaware of the rest or that we can't detect the rest or even render images based on frequencies well outside of the electromagnetic spectrum. An X-ray taken at the hospital is an example of a "camera" tuned to a different frequency. A heat-sensing camera is another example. Man uses such devices all of the time to detect weather conditions not readily visible or to map the energy dispersion of the universe. If one were to take a device designed to emit electromagnetic waves at a large range of frequencies, they could tune it to produce waves measuring 400 nanometers from crest to crest, the result would be what we perceive as a blue light. As the frequency of the electromagnetic energy is decreased the color will change to green, then yellow, orange and as the frequency approaches 700nm, red light. But if we continue to lower the frequency, we cease to see the electromagnetic wave produced. Eventually, the waves become "visible" not to our eyes, but to our radio receivers. A radio wave and a light wave are the same thing -- physical energy and part of the electromagnetic spectrum -- but at a different range of frequencies.
It may be fun to attempt to explain these simple photographic anomalies by suggesting them to be something as yet not understood or not recognized as existing to main-stream academia, but in the final analysis, they're simply "tricks of light" or similar phenomena, and display nothing to suggest they are anything but recorded light, in the visible spectrum, acted on by the optics utilized (lenses, apertures, etc.), to focus light reflected from surfaces at specific ranges.
