A Primer on Built-In DSLR Flash

I was amazed at how detailed the twinkling stars appeared as I was watched the first game of the 2008 World Series on an HDTV. Then I realized the game was taking place in the Tampa Bay Devil's enclosed Tropicana Stadium. Those weren't stars. They were thousands of individual electronic flashes capturing the first pitch of the game.

At that same instant, my mind flashed back to the first days of my photographic career when I managed a color lab and processed literally millions of similar pictures for amateur photographers. The events and pictures varied from Friday night high school football games from the top bleacher to parents recording their child's graduation from seat ZZ10, but the results were always the same -- great pictures of the backs of peoples' heads seated 3 to 4 rows in front of the photographer and no image of the event taking place 300 to 400 feet away.

The moral of the story is -- like Dirty Harry would say -- "a man (or woman) has to know his limitations." Limitations is the story of your camera's built-in, electronic flash. The camera's built-in flash is extremely convenient and useful within its effective range.

When taking a flash picture, the light rapidly spreads out to illuminate the subject (above). A portion of the light strikes the subject and is reflected back to the camera's lens. Because of the spreading of the light and the distance that light is required to travel (to and from the subject), much less light returns to the camera than was originally emitted by the flash unit. It's the returning light that determines the aperture setting needed for a correct exposure.

The illuminating power of a photographic flash unit is normally expressed as a guide number. A typical guide number for a flash built into today's DSLR is 40 feet at an ISO of 100. Photographers have used this guide number for years to determine the correct aperture setting (temporarily forget about the automatic flash function on your camera).

The math is simple. Divide the guide number by the distance from the flash to the subject. The result is the aperture setting. For example, a flash with a guide number of 40 and a distance to subject of 5 feet would require an aperture setting of f/8. (40 divided by 5 equals 8)

Back to the automation in your camera. DSLR cameras with an automatic built-in flash are capable of electronically determining the distance to subject and performing the math to set in the proper aperture setting.

So why did I drag you through this explanation and 4th grade math?

Knowing the guide number of your flash unit and this simple equation speaks volumes about what pictures you can and cannot take. If the subject in the example above had been 10 feet away from the camera, the required aperture setting would be f/4. (40 divided by 10 equals 4) This is probably very close to the maximum possible aperture setting of your camera. By the time the subject is 20 feet away from the camera, the required f/2 aperture setting isn't available on your camera. You have exceeded the effective range of the camera's built-in flash.

As shown in the illustration above, the typical effective range of the built-in flash units in today's DSLRs is from 10 feet to 20 feet. As you exceed the maximum effective range of the camera's flash, the subject will become increasingly underexposed (darker) until it is completely lost.

Remember using a telephoto lens does NOT help this situation. The effective range of flash illumination is always determined by the distance of the flash unit to the subject -- regardless of the lens being used.

Estimating the average distance from the bleacher seats to the pitcher's mound at Tropicana Stadium to be 300 feet to 500 feet or more, is it any wonder why these pictures never turn out as expected?

Even most professional external electronic flash units can't take this picture. A typical pro unit might have a guide number of 150. Doing the guide number math with this guide number yields a maximum flash-to-subject distance of 50 feet to 60 feet. (Probably explains why professional sports photographers are seldom found taking pictures of night games from the bleacher seats.)

But someone will say, "Hey, I took a similar picture, and it didn't look too bad." Truth be told, in these instances, the flash played NO visible role in the exposure. What produced the image was the available light provided by the stadium's lighting -- not the flash unit. Certainly the photographer saw the flash fire, but not enough light returned from the subject to make any visible exposure. It was the stadium light that made the picture possible.

If you find yourself in one of these seemingly impossible situations, try turning off the flash and use the light that's available in the arena. It may be necessary to increase the ISO setting to 800 or higher, but it's better than losing the picture opportunity.

Note: Guide numbers are directly related to the ISO setting of the camera. The higher the ISO setting the greater the effective distance of the flash unit becomes. This alternative provides a small gain in effective distance, but the trade off will be pictures that show more and more visual noise (grainy appearance) at each higher ISO setting.

One final cautionary note: Light emitted by the built-in flash unit "spreads out" at all angles when fired. One of these directions is downward.

Flash shadow created by a wide angle lens

This becomes important when using wide angle lenses. The flash picture above was taken with a lens that was too wide for the camera's flash. The result is the shadow seen on the lower half of the wall. The dark area is actually the shadow created as the light was interrupted by the top of the lens. Your camera's manual will indicate the maximum wide angle lens to be used with the camera's flash unit.

I will end this article with two other examples from my days managing a color lab for amateur photographers and processing thousands of pictures everyday. The first occurred when I covered the premier showing of the Star Trek movie for a local newspaper. After two decades of absence from TV, this movie was long anticipated. Sitting in the darkened theater, I couldn't believe my eyes when Captain Kirk first appeared on the screen and dozens of flash pictures were taken. You can't light up light. I saw those pictures pass through the lab the next day. What did these photographers get in return? Pictures of a completely white screen.

The second example occurred every day with a stream of flash pictures people would take of their TV screens. What did they get? Nothing but pictures of a bright flash reflected from the glass of the TV screen.

Know the limitations of the flash.

Equipment Tip - Lenses and Distance Distortion

I'm sure you've been asking yourself, "When is Hub going to show me how to take a picture of two basketballs at rest on a stone wall?" Well, today's your lucky day.

These two basketballs were shot using a 52mm (normal) lens.

To maintain my position of neutrality in the industry, I have intentionally selected a Spalding and a Rawlings basketball for this exercise in optical illusion. Actually I'm using these two basketballs to illustrate a photographic lens phenomenon associated with focal length - distance distortion.

The picture above was taken with my Canon DSLR's normal lens (52mm focal length). Notice the distance between the two balls. This distance was approximately what I saw with my own eye.

Contrast this image with the picture below:

This picture was taken with a 300mm telephoto lens.

I changed to a 300mm lens for this picture and moved my camera back until the first basketball appeared about the same size as it did in the first picture. I did NOT move the basketballs. Notice in this picture that the two balls "appear" to be much closer together. The rule is: the longer the focal length of a lens, the more it will compress the apparent distance between objects.

Here's one more example:

This picture was taken with a 17mm wide angle lens.

Again I changed lenses. In this case, I chose a 17mm wide angle lens. I moved the camera close enough to the first basketball to make it approximately the same size as the first picture. Now the distance between the two balls has "apparently" increased. However, I did NOT move the basketballs. The rule is: As the focal length of a lens decreases the apparent distance between objects increases.

The actual physical distance between these basketballs remained constant for all three pictures.

You see this optical phenomenon all the time on televised NASCAR or Indy races. The cars look as though they are stacked bumper-to-bumper from the head-on shot down the straight away (using a very long telephoto lens), but the side shot of the entire field reveals that the cars are 100 feet or more apart (using a wider angle lens).

You can use this optical reality in creative ways in your photography. Even if you're not after any special effect, you must remain aware that this distance distortion is always at play and changes as the focal length of your lens increases or decreases. (FYI: If you've examined the last picture taken with the 17mm lens closely, you'll notice that even the distance between the front and the back of the WNBA basketball itself has been distorted to give it that fat appearance. This is especially noticeable in the letters WNBA.)

Let me know if you have any questions or comments. You know where to find me.

Equipment Tip - Photographic Lenses

(This posting is intended to help beginning DSLR users make wise lens buying decisions. The more technical aspects and shooting characteristics of lenses can be found on my sister blog site: Hub's Camera at www.hubbardcamera.com.)

Probably the most often purchased piece of equipment for any DSLR owner (next to data storage cards) has to be lenses. They are also among the most expensive items you can buy for your photographic craft.

During the period of my career when I owned 3 camera shops, I was always intrigued by the lens choices my customers made. Eventually my interest in these decisions developed into a well practiced, educational, over-the-counter discussion which I made a point of having with anyone making their first interchangeable lens decision.

(For this post, I'm assuming the camera you bought included a "normal" lens in the 50mm to 58mm range. So, adjust this discussion to your own camera/lens combination.)

Well over three-quarters of my first time lens buyers would ask FIRST about telephoto or long zoom lenses. To this day, I find the preference for a telephoto lens as a first purchase interesting.

To my way of thinking and based on the photography challenges I faced as a professional, a telephoto or long zoom lens is not a high priority. Think about the types of photography you encounter. Birthdays, weddings, family gatherings, award ceremonies, baby's first steps with mom holding child's hand, etc.

In most cases, the event takes place in a confined space with lots of people in attendance. The challenge is to get all of the people or landscape into a single picture. Knowing that the majority of the pictures I will shoot fall into this category, I would FIRST buy a wide angle (fixed or zoom) lens. Granted there are those whose photographic specialty is taking individual people portraits or images of that deer on the ridge that's over a mile away where telephoto and long zoom lenses are a necessity. But they too have families and similar space confining events to cover.

To get our definitions straight:

• A "normal" lens usually falls in the 50mm to 58mm focal length range. This lens "sees" about the same amount of a scene as your own eye -- excluding your peripheral vision.
• A telephoto lens (usually lenses with a focal length longer than 58mm) makes objects appear closer, but "sees" less of the overall scene.
• A wide angle lens (usually any lens with a focal length less than 50mm) makes objects appear farther away, but it "sees" MORE of the overall scene. FYI: a lens with a focal length of approximately 21mm "sees" about what your eyes see -- including your peripheral vision.
  
• A zoom lens has the capability of varying its focal length over a broad range. Zoom lenses can be purchased that cover very wide angles to extremely telephoto. Each zoom lens will be denoted by the specific focal length range covered. (For example: one zoom -- a wide angle zoom -- might cover a range of 12mm to 24mm while another -- a telephoto zoom-- might have focal lengths of 100mm to 200mm.)

Not too many years ago, zoom lenses were the scourge of the professional photographic community. These lenses were notorious for their optical imperfections (aberrations). However, lens manufacturers, their tools and their techniques have come a long way to make modern zoom lenses a viable and often preferred choice for even the most discriminating photographer.

In fact, whether it's a fixed focal length lens or a zoom lens, you can rest safe in the knowledge that if you purchase a lens from a major manufacturer, you'll have a good chunk of glass that will take outstanding pictures.

So, my tip. I would start my lens collection with a wide angle zoom lens and make my next purchase a telephoto zoom lens.

Shown here is my Canon wide angle zoom lens (attached to camera) and my telephoto zoom lens. These are my photographic workhorses. I have a similar selection of lenses for my Nikon system. With these lenses I am assured of having the right focal length for 98% of my shooting situations. With only these two lenses in my camera bag, my total focal length range is 17mm to 300mm.

There is one more reason I recommend this type of lens combination. Less stuff to carry around. Instead of having ten fixed focal length lenses in my camera bag, I only have two. This makes bag searching quicker and lots less weight to carry in the field.

I hope you find this tip helpful. Again, visit www.hubbardcamera.com for more "techie" (but still beginner's) overview of DSLR camera lenses.

As always let me know if you have questions, comments or suggestions.