You are watching Digital Photography One on One, where we answer your questions. Here is your host Mark Wallace.
Welcome to the 1st Episode of Digital Photography One on One. In this episode we are going to be talking about some of the basics of flash photography. And just because this stuff is basic, it does not mean it is not important. In fact, this stuff is so important that it could revolutionize the way you use your flash. This is good stuff so let us begin by looking at some of the questions that were sent in. To get the best results when using a Canon 580 flash unit on a 20D, should I stick to ISO100? Would you ever change the ISO for some reason? Can you lease explain key shifting to me in regards to outdoor portraiture. Once I establish a meter reading on my subject of say f/8, what do I have to do to lighten and darken the background?
These are great questions. And the first thing we need to understand is how our camera shutter works. On most cameras the shutter is what is known as a curtain shutter. This is made up of two curtains that open and close to obtain a proper exposure and these curtains have names, the first curtain and the second curtain. They open and close to reveal the light to the sensor much like a actual curtain in a theater works to reveal what is happening on the stage. So, let us dive in and take a closer look on how this two curtains work. When you press the shutter release with your finger it tells the camera to open the shutter. The first curtain opens to reveal the light to the camera sensor then the second curtain follows behind the high delight. Then the curtains reset and wait for you to press the shutter release again.
Let us watch that again. You notice in this animation that the first curtain opens completely before the second curtain begins to follow. This only happens at slower shutter speeds. Usually speeds under 200 of a second. Now, watch would happen when we speed things up. When the shutter speed is faster, the second curtain cannot wait for the first curtain to open all the way. If it does, it would not make it across in time. Notice in this animation that the shutter is never fully opened. It just reveals a slit of light as it travels across the sensor. As the shutter speed increases, the slit become smaller and the curtains move faster.
Now, that you know how the shutter works we can begin to talk about a few things. The first is sync speed. Sync Speed is the shutter speed on your camera that allows the first curtain to fully open before the second curtain begins to follow. In other words, it is the fastest shutter sped you can use with a flash. Let us take another look at that animation, this time with a flash on the mix. When our camera shutter speed is set to sync speed slower a few things happen. When you push your shutter release button, the first curtain opens. And as soon as the first curtain is fully open the flash fires then the second curtain closes. Now, if we set our shutter speed too high, we will have problems. Let us take a look. When you press your shutter release, the first curtain will begin to open, but before it is fully opened the second curtain begins to close. When the first curtain is fully opened, the flash fires just like it did before. But this time part of the sensor is covered by the second curtain. This will cause our photo to have a black area. And the faster your shutter speed the more black you will have on your photo. To make sure you do not have this problem always set your shutter speed to your cameras sync speed or slower. Sometimes sync speed is called x-sync. X-sync and sync speed are the same thing. You can find out where your camera sync speed is by looking in you user manual. For most cameras it is 1/200th of a second. You my even notice that I keep saying, if you set your camera shutter speed, the sync speed or slower that is because if you slow down your shutter speed, you can create magic. That is because you are actually controlling two exposures at the same time. You are controlling the ambient light exposure that is anything, any light that is not coming from your flash and you are also controlling the flash exposure. That is the light that is coming from your flash.
Now, to help you understand this, we are going to do a little exercise. We are here in the parking lot of our studio. And it is not a very glamorous location, but it is a perfect location for this demonstration. I am keeping this simple by using just a single pro-photo head and a soft box. And this is going to give a nice soft light on our model here. This is Megan. And I have already metered this, so I have my camera set to 1/250th of a second which is my sync speed and this is metered at f18. So, I am going to take two pictures, the first without a flash and the second with a flash. Look right this way Megan, look right at me. Gorgeous! Just like that, perfect. Let us take a look at that photo. Now, this photo is absolutely black. That means at 250th of a second in f18, there is not enough ambient light to get a decent exposure.
So now, let us take another shot. This time with the flash on, there we go. Wow! Look at that, in this shot Megan is lit, but the background is still totally black. What that means is that the only light that the camera sees is the light that is coming from the flash. Now, if we want more ambient light what we will need to do is slow down the shutter. So, what I am going to do is I am going to take a series of shots progressively slow down the shutter so you could see how dramatic this is.
And that is key shifting, simply using your shutter to show more or less ambient light by either slowing down the shutter or speeding it up. Now, if you do not have a fancy light meter and a pro-photo setup with a soft box you could still do this. You can just use an on camera flash like an icon speed light or Canon 550, 580, something like that. And actually the camera will do most of the work for you. Simply put your flash on your camera, set your camera to manual mode and then set your aperture setting to something about 4.5 and your shutter speed to around 200 of a second. Then take a photo, slow down your shutter speed, take another photo, slow down your shutter speed again and take another photo and just keep going to see what happens, it is a lot of fun. Let us try it.
That was a lot of fun. Thanks a lot Megan. So, remember if you are in a low light situation, you can always increase your ISO setting. Doing that makes your sensor more sensitive to light and so your shutter speed does not have to be so long to get that ambient light and a picture, just simple as that.
Now, if you have a question for Digital Photography One on One, just send it in tostudiolighting@gmail.com. I will see you next time.
This episode is brought to you by snapfactory.com and studiolighting.net. For more information about our workshops, visit snapfactory.com.
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