Is that white spot a ghost?

One of the major shortcomings in compact camera design is the close proximity of the flash to the lens.  The most common problem caused by this design is red-eye.  A second problem directly related to the close flash/lens proximity is the presence of random white circles appearing in images.  A universal term does not exist to explain these circles though I like to refer to them as “ghost spots” because they’re semi-transparent and appear in different locations in subsequent images.  The explanation for this second flash-related problem is very similar to that of the red-eye phenomenon.

Ghost spots are created when light from the flash reflects back off of dust particles floating in the air close to the camera. Because the lens is focused on a subject further away than the dust particle, the illuminated particle is out of focus and appears very large in the form of a white circle.  The close proximity of the flash to the lens makes compact cameras more susceptible to this problem than DSLRs.  The problem is also common with wide-angle lenses because of the wide field of view.

The following image is an example of ghost spots.  The background is an auditorium curtain.

Common particles that cause ghost spots include:

• dust

• smoke

• pollen

• moisture in the air

To eliminate or reduce the number of ghost spots you can use the following methods: (note that many of the following are the same methods used to reduce red-eye)

• Turn on more lights.  Having more ambient light allows the flash to fire at a lower power.

• Increase the shutter length.  A longer exposure will capture more ambient light and the flash can be fired at a lower power.

• Increase the ISO setting so the flash can fire at a lower power.

• Turn off the flash if there is enough ambient light.

• If your camera allows for it an externally mounted flash will increase the distance between the flash and lens.

 

Understanding and Reducing Red-Eye

We’ve all seen pictures spoiled by the iridescent glow of bright red eyes that look like something out of a sci-fi thriller.  So what is this phenomenon?

When photographing with a flash that’s located close to a lens the light reflects back off the blood rich retina towards the lens, creating the dreaded red-eye effect.  Red-eye is most prevalent in scenarios where the natural light source is weak, such as nighttime and other dimly lit scenarios because our pupils dilate to compensate for the low levels of light.  A wider pupil exposes more of the blood vessels in the retina and the camera relies on a stronger flash to illuminate the dark scene, in turn enhancing the red-eye effect.

The close proximity of the flash to the lens is a shortcoming of nearly all compact cameras simply because of the physical size of the camera.  Even DSLRs using built in pop-up flash can create red-eye.  So how do you prevent red-eye from occurring in flash photography?

In some cases it’s not possible to eliminate red-eye completely, though there are practical methods you can use to reduce its effect.

• Most cameras incorporate some type of red-eye reduction system.  Right before you take the picture the camera will fire a pre-flash or series of flashes causing the iris to close the pupil.
• If you are indoors a simple solution is to turn on more lights or move the subject closer to a window (provided it’s light outside).  The effect is two-fold; having more ambient light causes the pupils to constrict and also means the flash doesn’t have to fire as strongly to illuminate the subject.
• An alternate method to increasing the available light is to increase the shutter length.  A longer exposure will capture more ambient light and the flash can be fired at a lower power.
• Increase the ISO setting so the flash can fire at a lower power.
• If your camera allows for an externally mounted flash it’s worth investing in a flash unit with a tilting head.  Mounting a flash on the camera automatically positions the flash further from the lens than the built in flash.  A tilting head allows you to point the flash in multiple directions and bounce the light off of a nearby surface instead of pointing it directly at the subject, eliminating the direct reflection from the retina.
• To move an external flash even further from the lens a flash bracket can be used.  An added benefit to using a bracket is the ability to position the flash above the camera while holding the camera vertically.
• If all else fails you can use photo-editing software to remove the red-eye.  However, the resulting image may not look as natural as an image captured without red-eye.