When I first started capturing perfectly round, white circles on my digital camera, I was excited. I thought this just might be some hard evidence of the 'paranormal'. But I decided to suspend judgement until I checked out all possible alternate explainations. I posted to the ghoststudy.com forum, asking if there was any logical explaination for these 'orbs'. Several people with technical experience in photography were kind enough to point me towards information about lens flares, a relatively common technical phenomena often mistaken for ghostly 'orbs'.
Here is a synopsis of what I learned:

Physics of Lens Flares

In order to take a picture, light must travel through different parts of a camera lens. When the light travels through each part of the camera, secondary reflections can occur. These can show up in the form of spots (orbs) or banding. Photography experts actually call this phenomena 'ghost'! These secondary reflections occur when the camera lens is pointed at a bright light source, such as the sun. In order to reduce the flare effect, many camera lenses have special anti-reflective chemical coatings.

Lens Apeture Blades

Lens apeture blades control how much light will enter by adjusting something called the 'f-stop'. Constricting or expanding a set of blades that form a circular shape adjusts the f-stop. The area where two blades meet is more reflective, and can cause a streak reflection across the film. (I'm not sure if this can apply to digital cameras as well). A lens with six blades, for example, can produce six streaks which are focused on a point, which becomes the center of the lens flare. The apeture blades also control the shape of particles reflected off various parts of the lens inside the camera. The reflection particles usually occur in a line that passes through the center of the lens and of the light source.

Dust on The Lens

This is another very simple explaination for many apparent 'orb' anomalies. Be sure to wipe off your camera surfaces before each investigation. I reccomend Endust for Electronics, which are individually packaged wipes. Dust on the lens is probably the explaination for many of the orb photos featured on this site.

Conclusions Regarding Orb Pics on My Site

I will no longer be posting orb pics taken in my condo to this website unless I can be sure about ruling out lens flare and dust. I will not pull down the current orb pics, but I will amend them with a link to this page and a disclaimer that there is probably a logical explaination for these orbs.

Is There A Logical Explaination for ALL Orbs?

As a novice investigator who is pretty new to all this, I can't offer anything more than my own subjective opinion on this matter. I think that many, if not most orbs have logical explainations. However, I cannot account for those who have captured orbs in motion on camcorders. The orbs in my pics did not show up on the digital display screen that I know of, only in the pic, which leads me to think it was dust on the lens.

When I first learned all this, my enthuseasim was initially dampened. I've been having my doubts about every apparent anomaly pic I have taken thus far. But I am just as enthusiastic about approaching the feild of paranormal investigation as an honest skeptic, and learning about the practical and technical aspects. I don't think that every anomalous picture, video, and EVP out there can so easily be explained away. I believe that most of them can, and the serious investigator should adhere to stringent protocols. But there is still something out there that science cannot currently fully explain. Whether it is something physical or 'supernatural' doesn't matter to me, only that there is a frontier still yet to be explored.