Flash-a Review

Flash Freezes• For most of our applications flash will

freeze any motion

• Flash is metered through the lens.

• When enough light has bounced off the subject and hits the sensor the flash is cut off

Flash doesn’t care much care about the shutter speed

• There is a maximum shutter speed that the camera will allow us to use with the flash turned on

• Different cameras are different but it’s usually about 1/200 sec.

• Speeds slower than that, such as 1/125, 1/60, etc. will not effect the flash exposure

Modern flashes don’t much care about aperture either

• The aperture will not make the exposure from the flash more or less (because the camera reads the amount of light coming hitting the sensor)

• But…..

A little bit of physics

• Light like other electromagnetic radiation obeys the inverse square law

• The intensity varies as inversely as a square of the distance.

• That means that every time light goes twice as far it has a quarter of the intensity

• Tell that to the folks with their cameras in the back of the concert hall

• So…

The inverse square lawthere’s trees back there but not enough light

What that means for us• The through the lens (TTL) metering takes

care of the exposure until the flash is putting out it’s maximum power and then

• “I’ve done all I can do and I can’t do no more, open up that lens and let the glass do the work”

• Actually do the math.• If the camera is set to iso 400 and the flash is

putting out maximum power and at f 8 the flash gives us correct exposure at 12 feet, at f4 it will give us the correct exposure at 24 feet, but

Hey that means that

• Yes! at f 2 it will give us the correct exposure at 48 feet.

• Now pump up the iso to say 1600 from 400 and f 2 will give us the correct exposure at 96 feet. Hey we can use flash from the back of the crowd but..

I don’t like this atmosphere

• If the air is smoky (used to be a big problem but finally the politicians did something for photographers), or dusty, or there is mist or rain or snow

Or Mosquitoes

• Our flash will light that up. (Oh no! it’s the inverse square law coming back at us and it’s not friendly)

• That being said we can light up far away things with out flashes.

In the Nice Clean Air

Why does flash look like flash?

• It lights up close things more than far things. (It’s not just a good idea, it’s the law)

• It is close to a point source (very hard edged shadows.)

• It is close to the axis of the lens so the light is coming back at us and it’s not friendly.(If you wonder why faces are shiny with flash it’s because they are acting like mirrors)

What can we do?

• Live with it.

• Keep important things about the same distance away from the flash

• If you can’t keep them the same distance keep them as far away as possible

Pretty Even

What else we can to

• Bounce it. The flash is going further so the you-know-what isn’t so bad, and it’s no longer a point source, and light is bouncing all over the place lighting up the shadows, but

• Don’t get too close, especially to us old folks because

• The light goes straight up and comes straight down making all kinds of shadows under eyes etc.

The ball don’t bounce if there ain’t no wall

• If there is no ceiling or the ceiling is high or painted a dark colour it won’t work

• If it’s painted a funny colour let’s hope you subject looks good in that colour.

If you can’t beat it modify it

• There are many things you can stick on your flash to make the light nicer

• A diffuser is still directional but it bounces light all around the room to fill in the shadows. Try a foam coffee cup.

• A piece of card or paper attatched to the top of flash that is being bounced will reflect light into the shadows that are created with the by the light bouncing off the ceiling.