Photo Technical

Science of flash options reveals complexity of light, a vast topic – A44

This is the fifth installment covering camera specifications you can find on such websites as The fifth installment!  When first thinking of writing about specifications I thought they would be covered in two articles, that’s it.  Then I was concerned that systematically following a list might be boring.  I hope not.  I am well past two articles now, and the information included in these articles should of interest and helpful to any aspiring camera bug.  After all, specifications are a list of facts about your camera, and I’m providing a more in depth translation of what they mean and how they work for you.

For continuity I continue to use the randomly chosen Lumix DMC-FX150 camera, manufactured by Panasonic.  We ended on Max shutter: 1/2000 sec the last go around, and move on to:

Built-in Flash:  Yes – Can’t imagine a pocket camera manufactures without one.

Flash range: 5.9 m (Auto ISO) – This speaks to the power of light output of the built-in flash.  Photography is all about light, and has been expressed as “painting with light.”  Light is a favorite subject of mine that can get complicated, so writing a KISS version is more fun and challenging.

The power of a flash is given by the (seldom published) GN of guide number, which is as a standard determined at an ISO of 100 (sensor or film sensitivity to light).  Let’s say the GN is 56.  This means at 10 feet at ISO 100 the flash will work up to 10 feet in distance at f/5.6.  This is calculated by dividing the GN of 56 by 10 feet.  The outcome f/5.6 is the highest/smallest aperture (controlling depth of field) on this Lumix.

Having expressed the more complicated part, what does the specification 5.9m (Auto ISO) mean? I guess it means that at f2.8 (the lowest/widest aperture for this camera) with the highest Auto ISO of 1600 the flash of light will reach outward to 5.9 m (1 meter = about 39 inches) or 19 feet… WOW!

Just kidding, there’s nothing to really WOW about.  From here it gets tedious, so let’s just go straight to the KISS part.  Pocket flashes put out very little usable light.  The ISO 1600 has a lot of noise, so not a desirable setting.  I have found ISO 800 in some cameras not too bad, and things really improve at 400 or less, with the best ISO setting always the lowest setting, which in this LUMIX is 100.

Unfortunately, when using flash this camera system uses Auto ISO settings, meaning you have no control – period, except to avoid subjects at 19 feet distances.  After making calculations using another light output formula called the Inverse Square Law, I figured out this built-in flash at ISO 400 carries at most 9 feet.  Bottom line, for a quality image using this flash keep subject to a distance of 9 feet or less (and this is the case for nearly all compact cameras).


External flash: No – This means this pocket camera (as is true of nearly all of them) has no “pc” connector to physically cord an external flash to the camera.  You might ask why you would want to.  There are a number of reasons it could be useful to have this ability.

First, as we have already discussed, the in-camera flash lack of light output power limits it’s usefulness.  I have several portable flash units; one type has a GN of 197 at ISO 100, meaning that at f2.8 the range would be 71 feet (or 22m).  At 1600 ISO it would carry 60m and possibly more.  Compare this to the LUMIX flash range of 5.9m to better understand the difference.

Let me tell you, if my camera had access to a more powerful flash I would not use f/2.8 or 1600 ISO, but more optimum settings like f5.6 and ISO 100 or 200.

Second, an external flash would allow you to be more creative with your lighting, allowing for high or low 45 degree or side angles of light, and to create backlight behind a subject.

Third, the built in flash is too close (in nearly all pocket cameras) to the optical axis of the lens, therefore red eye is always an issue.  Red eye is a photographic phenomenon related to light from the flash entering into the pupil and reflecting back the blood from behind the retina.

Keep in mind you have to use a flash when it is dark, and this is when our pupils (similar to camera shutters) are wide open to admit more light for night vision.  So when the flash catches a wide open pupil the red eye effect is maximized.  This is why “pre-flash” was developed to throw out light in advance of the actual flash in order to close the pupil and thereby minimize the red eye effect in the actual (flash) exposure.  In any case, an external flash would eliminate red eye problems.


I’ll close this with a question to you.  Even though the specifications state “no external flash” it is possible to use one.  Anyone out there want to give me the how to answer?  Send me an e-mail.  The first received will be the winner.  While you’re at it, send any photography questions you have…for answers.  In the meantime I’ll take permission to go ashore.  Happy sailing!