Advanced Video Editing



JVC GY-HM600/620 Camera

Getting the Exposure Right

The best looking video is that which 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
  • Gain
  • Shutter Speed
  • Iris

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

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 adjust exposure manually. But when you want the most control over the picture quality use MANUAL.


To adjust exposure manually you need to set the camera to MANUAL operation mode. 

Switch the FULL AUTO button to OFF - this sets the camera to manual operating mode. You're now ready to adjust the exposure manually.



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. 

Ascertain the lighting in your environment and turn on the ND filter according to the brightness of the object. The selected ND filter is displayed in the monitor and viewfinder screen. The camera will display an ND filter warning when it becomes necessary to prompt you to select an appropriate filter. 


There are three ND filters to choose from: ¼, 1/16 and 1/64

If you start with ¼ and the image is still too bright, switch to the next filter. When shooting under very bright conditions, the diameter of the iris may become extremely small, causing what is known as “small aperture diffraction” where the image may appear blurry or hazy. Should this occur, the camera will display an ND filter warning. 


Gain

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 – it does not! The 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 LCD monitor and viewfinder. Zero dB 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.

It’s important to understand that 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, to get proper exposure always start by making sure the Gain is off, or 0 dB.

Remember, you’re not the only one who will be checking out this camera for class; the student 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. The default setting for L will always be 0 dB, or no Gain. The M setting will be set to 6 dB and the H setting to 12 dB. These values can be changed in the menu settings. 

Press the GAIN button to toggle between manual and automatic gain. When the Gain is set to automatic, an A icon appears on the LCD Monitor/Viewfinder next to the gain value. Manual Gain is simply switching between L, M and H. 


Remember, if you have to use Gain to make the picture look brighter, then that’s a sign you should be using additional lights. Don’t rely on Gain when additional lighting will make your picture look better. An underexposed/overexposed picture, or a grainy one because the gain is set too high, is simply a rubbish shot, which is unacceptable to professional standards.


Shutter Speed

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 if 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, which results in underexposed images. To compensate, video shooters add more light to get the same level of exposure, such as opening the Iris further to get more light to enter the lens. 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 so you can get more light to fall on the camera’s sensor.


Press the SHUTTER button, which will toggle between Automatic and Manual Shutter modes. In Automatic Shutter mode an A icon appears in the LCD Monitor/Viewfinder next to the shutter value. 





In Manual Shutter mode, press the SET button (which is the centre of the cross-shaped button) to switch between modes and the up and down button to change speeds.

When you press the Up or Down buttons, the shutter value will be highlighted in the LCD Monitor/Viewfinder. Press Up or Down to change the shutter speed.




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. 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). 


Iris (Aperture)

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 is measured in f-stops, which describe how much light enters the lens.

F-stops are numbered in the following sequence: f/1.4, f/1.6, f/1.8, f/2, f/2.2, f/2.5, f/2.8, f/3.2… all the way up to f/11. The smaller f-stops correspond with a larger aperture (more light can enter the lens) and the larger f-stops to a smaller aperture (less light can enter). 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.


Adjusting the Iris – as long as the camera is in MANUAL operating mode, press the IRIS button. This button toggles between the Manual and the Automatic Iris modes. When you set to Manual Iris mode, the A icon next to the f-stop values will disappear. Then turn the Iris ring on the lens to change the f-stop value.







PUSH AUTO 
- When using Manual Iris mode, pressing this button will change the mode to Automatic temporarily. The iris will change automatically according to the brightness of the object. 

When using Manual Iris mode, the f-stops can be changed by turning the Iris ring on the lens. 

The f-stop values will vary depending on whether you're using the wide end or the telephoto end of the lens.

Wide end - f/1.6

Tele end - f/3.0



Exposure Assists

Zebra (User 5 button)

You can apply a monitoring tool called Zebras that show up in parts of the image that are brighter than a predetermined level. Zebra stripes help you know at a glance what areas are too bright, and possibly overexposed. You can then reduce the iris to eliminate Zebra, but it’s not crucial to eliminate them entirely; it might be unavoidable in some things like the sun or light bulbs, but it’s best to avoid Zebras showing up in the sky and even on white buildings or cars. When shooting interviews, you don’t want to see Zebras on the face except maybe on little bits of the forehead or nose where they tend to be shiny.


Press the ZEBRA/5 button, which will then display zebra stripes over areas of the picture that are overexposed. When the Zebras are activated an illustration of a zebra is displayed in the monitor/viewfinder. The stripes are drawn only on the monitor/viewfinder image and are not recorded into the picture itself. Pressing ZEBRA/5 again will turn the Zebras off. 




As the picture above shows, when ZEBRA is activated, parts of the picture that are overexposed will show stripes. The Zebra stripes alert you to overexposed areas of the picture so you can take steps to correct the exposure.