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.

Why Pixel Size Matters

Thanks to the marketing of retailers and manufacturers, consumers have been led to believe that more pixels equates to higher image quality.  With more pixels consumers are left with the option to crop images tighter on a computer to compensate for the shorter focal length lenses typical of point and shoot cameras.  However, new point and shoots still won’t produce as high quality of an image as those produced from a professional or consumer grade DSLR with the same number of pixels.  Lens quality has an effect, but sensor size is the key factor here.

A single frame of 35mm film measures 36mm x 24mm.  A digital sensor with those dimensions is called “full frame”.  There are only a few pro-level cameras (currently $3000 to $8000) that contain this size sensor.  A more common sensor size found in many consumer level DSLRs is 22.5mm x 15mm (with slight variations), referred to as APS-C, with prices ranging approximately $700 to $1500.  Point and shoot cameras have a range of sensor sizes with many commonly around 7mm x 5mm, about the size of a small fingernail.

The following image shows the relative sizes of three 8mp Canon camera sensors.

 

Because all three cameras have 8 megapixels it’s obvious that individual pixels on the point and shoot SD850 sensor are drastically smaller in comparison to the pixels on the professional 1D mkll DSLR and consumer grade 20D DSLR sensors.

So why is image quality better on cameras with larger pixels?

To create a print an image captured on a smaller sensor needs to be enlarged more than an image captured on a larger sensor with the same number of pixels.  In short, the smaller pixels get “stretched out” a lot more.  But there are more benefits to having larger pixels than just the amount of “stretching”.

Larger pixels have more surface area for gathering light, resulting in each pixel capturing a wider dynamic range (information between light and dark).  This is because more possible variations of light can be collected before the pixel reaches maximum capacity.  The image captured will contain more detail in transitions between light and dark areas and will contain less digital noise than an image captured on a smaller sensor with the same number of pixels. 

For more in depth information on dynamic range and digital noise please refer to the following articles found on dpreview.com:

www.dpreview.com/learn/?/key=Dynamic_Range

www.dpreview.com/learn/?/key=noise

this, that, and the other thing

As a special event and sports photographer (primarily high school and town sports), I’ve had the pleasure of meeting countless individuals who share a wide variety of interest in photography.  Parents want to know how to take better pictures and some times just enjoy the chance to pick at the brain of a professional photographer.  I’ve had the privilege myself of picking at the brains of countless other photographers and continue to do so whenever I get the chance.  Photography is a never-ending learning process.  There’s always room for improvement and alternative ways to approach the same problems.

I’ve created this blog to share with you some of the best photographic resources I’ve found, provide answers to some of the most common questions I’m asked, and as a place to share some of the tips and tricks I’ve collected along the way.  Hopefully you’ll find this to be a helpful resource and continue to check back as this site grows out of it’s infancy stage.