JVC GY-HM170 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

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, especially over exposure, always use MANUAL.


Press and hold the FULL AUTO button located on the left side of the camera until the display changes. You will see either an A or an M displayed at the bottom of the monitor. When you see A, all the camera operations, minus the focus, will be done automatically by the camera; when there’s an M, the camera operation is set to MANUAL.


 

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 two ND filters to choose from: ¼ and 1/16.

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 the 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 L setting will always be 0 dB, or no Gain. The M setting will likely be set to 6 dB and the H setting to 12 dB. These values can be changed in the menu settings.



 

Remember, if you have to use Gain to make the picture look brighter, then that’s a sign you really should be using additional lights. Don’t rely on Gain when additional lighting will make your picture look better. An underexposed picture 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 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 allow 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.

To set the Shutter Speed manually, press the SHUTTER button, located on the lower left-side portion of the camera. Pressing this button will highlight the shutter speed value in the monitor or viewfinder. Once the value is highlighted, use the toggle switches to the right of the SHUTTER button to set its value. Press SHUTTER again to de-select 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. 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. 


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 A/M button on the left side of the camera. This button toggles between the f-stop (Iris) and the AE Level display (an explanation for AE Levels is below). The IRIS A/M will set the iris to Auto mode and the camera automatically adjusts the exposure according to the brightness of the object. The f-stops are not displayed in the Auto mode. 



To adjust the Iris manually, make sure the f-stops are displayed in the monitor/viewfinder. Press the IRIS A/M button until the f-stops are displayed (the camera is now set to Manual Iris mode). Turn the Iris dial (the knob directly in front of the IRIS A/M button) to change the aperture size. Or turn the Iris ring on the lens. 





You can also change the iris by turning the Iris Ring, which is located just behind the Focus Ring. 



Using the AE Level

The AE Level is a way to put the exposure settings well within your control. Because there are many variations in lighting, cameras don’t always get the exposure just right. AE is a form of exposure compensation that lets you adjust in “plus/minus” settings how much lighter or darker you want the exposure to be. The actual exposure settings are not changed, but rather you’re just telling the camera that you want to adjust what it’s calculating for proper exposure. For example, if you’re photographing a person on a bright sunny day with a bright background, the camera will calculate the exposure based on mostly the bright light. What you will end up with is a person who appears dark, or backlit. If you dial up the AE numbers, you can make the person appear brighter.

You probably don’t need to worry about changing the AE Levels for the majority of your shots, especially as a beginner. But as you get more experienced, you’ll find the additional functions on the camera will let you take more control over the shooting process.




Usually, AE is set to 0 where the camera will make the exposure without the photographer’s input. You can slide the AE value to either -2 (darker) or +2 (lighter), which forces the camera to adjust its calculated exposure darker or lighter. 








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 an 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 illustrated 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. 



Above is an illustration of Zebra showing areas of the picture that are overexposed. Use Zebras as a guide to help you avoid an overexposed image.