Getting the Exposure Right
The best looking video is video that is exposed properly. The key concept to understanding exposure involves the amount of light that reaches the camera’s sensor – too much light and the image will be blown-out, or overexposed; too little and the image will be dark, or underexposed. Bad exposure is simply unpleasant to watch and is, therefore, not acceptable to a professional broadcast.
Getting the right amount of light to enter the lens will produce excellent results. It’s not as hard as you think, not if you commit to memory the following checklist in this order:
- Neutral Density (NF) Filter
- Shutter Speed
How you set each of these items in the checklist
will help you control the amount of light that enters the lens
Switching the camera between automatic and manual mode
First, make sure the camera is set to MANUAL operation mode. There is a very good reason to use manual rather than automatic - don’t trap yourself into thinking that automatic will do all the hard work for you. AUTO is useful only under certain circumstances when it becomes difficult to manually adjust exposure. But when you want the most control over the exposure, always use MANUAL.
Switch the FULL AUTO button from ON to OFF. If the camera is in Automatic mode, you will see the FULL AUTO icon appear in the lower left of the OLED screen. In FULL AUTO mode, all the exposure operations will be done automatically by the camera. Rather, you need to learn how to operate the camera manually. So make sure the FULL AUTO is off.
Neutral Density (ND) Filter
The ND filter is the first thing you should check on the camera. Think of the ND Filter as “sunglasses” for the camera – you put sunglasses on whilst outdoors on a sunny day and you take them off indoors. The ND filter is used only in bright environments, typically outdoors, and it’s not necessary to use it indoors unless the lighting is particularly bright. Using the ND filter enables an appropriate range of f-stops when you start adjusting the exposure.
Fortunately for TV Reporting students, the ND filter on the Canon XF200 operates automatically depending on where you set the f-stop (aperture) value. When you work with other cameras, however, you will need to be conscious of the ND filter settings.
Strictly speaking, Gain electronically boosts the video signal under low light conditions to artificially make the image look brighter. The common misconception is that Gain allows more light to enter the lens, but this is not technically correct! Gain is applied only in low light situations and only as a last resort to get more brightness out of the image.
Because Gain is signal strength, it’s measured in decibels (dB). You can see the Gain values displayed in the OLED monitor and viewfinder. Zero dB (0dB) means there is no gain at all, and every 6dB of gain doubles the brightness of the picture. But the more gain gets added, the more noise appears in the image, which is another reason why Gain is used sparingly and as a last resort. If your picture is too dark – it’s best to get additional lighting than have to rely on gain, especially when shooting interviews.
NOTE: Gain only amplifies the video signal, but it doesn’t add detail that is currently not visible. At high gain settings, the image will start to look grainy.
Before you can adjust the Iris and Shutter Speed, always start by making the sure the Gain is off, or 0dB
NOTE: You’re not the only student who will be checking out this camera for class; students before you may have left the Gain on and that could ruin your shot unless you do something about it first.
Gain on the camera is adjusted between L, M and H settings, which are pre-set in the camera’s menu. The L setting will always be pre-set to 0dB, or zero Gain. The M setting will likely be set to 6dB and the H setting to 12dB. These values can also be changed when using Manual Gain.
Before you change the Shutter or Iris (Aperture) settings, set the GAIN switch to L, or 0dB.
AGC – Automatic Gain
Using the joystick, press SET and push the joystick left/right until the gain mode icon in the OLED screen is highlighted. Then push the joystick up/down to select the A icon and then press SET. The current position of the gain switch will be set to automatic gain control.
Using the joystick, press SET and push the joystick left/right until the gain mode icon is highlighted, select the M icon and press SET. The current position of the gain switch will be set to manual gain.
NOTE: If the Gain on your camera is set to automatic mode, and the light levels are too low, the camera might set the gain too high, which will add noise to your image, thus drastically reducing its quality. Such a situation like this is a signal that you definitely should be using additional lights. Don’t rely on Gain when additional lighting will make your picture look better. An underexposed picture with too much noise is simply a rubbish shot, and that is unacceptable to professional standards.
Think of the shutter as a gate that opens and closes; when closed, light is prevented from reaching the sensor. Video shooters typically think of using shutter only when they are recording scenes with fast action, such as sports events. Changing the shutter to a faster speed helps prevent motion blur. But faster shutter speeds means the gate isn’t open long enough to allow as much light to enter the lens, and this results in underexposed images. To compensate, video shooters add more light to get the same level of exposure, such as opening the Iris (Aperture) further. When the shutter speed is slower, the gate is open longer and more light can reach the sensor.
In almost all normal circumstances, the minimum value to set Shutter Speed, and avoid motion blur, is 1/60th of a second. If you’re shooting under fluorescent lights, you definitely need to keep the shutter speed at 1/60th. In North America, fluorescent lights always flicker at 60Hz frequencies (in Europe, the frequency is more like 50Hz). Changing the shutter speed to anything other than 1/60 might cause noticeable orange bands or scrolling waves in your video.
Become aware of the Shutter Speed settings in your camera before you change the Iris. That way you can be assured that enough light is reaching the sensor so you can properly adjust the Iris (Aperture). As a guideline, start with the Shutter Speed at 1/60th and adjust to a faster speed if you’re shooting events with fast action, such as sports. But add speed only after you adjust the Iris. Remember, when you use a faster speed, less light will reach the camera’s sensor. You’ll need to compensate by opening the Iris (aperture) further.
To set the Shutter Speed manually, switch the SHUTTER to ON. Read the directions below to change shutter modes between automatic and manual.
Automatic Shutter Speed
Set the SHUTTER switch to ON.
Using the Joystick, press SET and push the joystick left/right until the shutter speed mode icon is highlighted.
Push the joystick up/down to select the A icon and then press SET. The shutter speed will now be set automatically.
Manual Shutter Speed
In manual mode, you can set the shutter speed according to your shooting needs.
Set the SHUTTER switch to ON. Using the Joystick, press SET and push the joystick left/right until the shutter speed mode icon is highlighted.
Push the joystick up/down to select the M icon and then press SET
If the SHUTTER switch is set to OFF, the shutter value will remain at 1/60.
This is the last item on your exposure checklist, which you can adjust only after you’ve ascertained the other items. The aperture is simply the hole in the lens that allows light to enter. The Iris is the mechanism that controls the size of the aperture and the amount of light that gets through. The changes in the Iris are measured in f-stops, which describe how much light enters the lens.
F-stops are numbered in the following sequence: f/1.8, f/2, f/2.2, f/2.5, f/2.8, f/3.2… all the way up to f/16. The smaller f-stops correspond to a larger aperture (more light can enter the lens) and the larger f-stops to a smaller aperture (less light can enter). For example, an f/2 admits more light than an f/8. With each setting, or stop, roughly half as much light enters the lens.
In most cases, you won’t need to know specific f-stop values to get the right exposure. Just understand that f-stops describe how much light enters the lens. In low-light environments, you would need to use a lower f-stop to get as much light to enter the lens as possible for a picture that is exposed properly.
When changing the following modes, make sure the FULL AUTO switch is set to OFF.
Setting the Aperture to Automatic Mode
Switch the IRIS (ND) to A. An A icon appears on the OLED screen next to the aperture value. The aperture values will change automatically depending on the lighting.
Setting the Iris to Manual Mode
Make sure the IRIS (ND) switch is set to M.
You’ll see the M icon appear next to the aperture values in the OLED screen.
Turn the Iris Ring on the lens (see below), to change the aperture values. The values will be displayed on the OLED screen in ¼ increments.
This bar is displayed only when the gain, iris and shutter are all set to manual adjustment. Use it as an exposure assist to help you gauge the current exposure. The downward-facing arrow in the centre indicates optimal exposure. The indicator inside the bar shifts along the gauge depending on the lighting conditions; when the indicator shifts left of centre the picture is underexposed; to the right the picture is overexposed.
Exposure Assist Options
The Canon XF200 offers 2 options to help assist you with getting the proper exposure.
The Zebra feature shows black and white diagonal stripes over areas that are overexposed. Zebra identifies areas within a certain exposure range that is pre-set in the camera.
Press the ZEBRA button to activate the stripe pattern. Press the button again to turn off the pattern.
The Canon XF200 can display simplified waveform monitor and vectorscope. To display the scopes, press the WFM button to toggle between the waveform monitor, vectorscope and the edge monitor. The scopes will appear in the lower right of the OLED screen.
Using the Waveform Monitor
The waveform monitor gauges the luminosity, or brightness of the image. The brightest areas of the screen, or highlights, shouldn’t exceed 100 on the gauge; the darkest areas shouldn’t fall below zero.
The picture is overexposed if most of the pixels collect near 100;
The picture is underexposed if the pixels mostly group near 0.
Using the Vectorscope
This scope gauges how much colour is present in the image. The squares represent, clockwise from the top, RED, MAGENTA, BLUE, CYAN, GREEN and YELLOW. The vectorscope may be very useful when you try to gauge whether the picture is white balanced or whether you have too much colour saturation; too much blue and the pixels will group towards the blue end of the scope; too much red and you’ll see pixels collected towards the red side.