I hire other photographers all the time to help out with youth sports shoots.
Before we take any photos, I take flash meter readings so we can be sure the fstop, iso and shutter speed are set to correctly get a great image in front of the greens screen while using our studio lights. I also want to be sure the lights are more powerful than the available, or ambient, light.
Some of these shoots are done outside, in tents, so the ambient light can become an issue if it’s a bright sunny day. I asked one of my photographers to tell me what the camera’s exposure was for ambient light according to the camera’s light meter. He looked at me like I was crazy. I had the flash meter in my hand and he had no idea that there was a light meter built into every modern camera to show you what your available light exposure is based on current camera settings.
The flash was giving us an exposure of F8 at 1/160 of a second at iso 100. I wanted to make sure the available light exposure would be under exposed enough so the flash was the providing the heavy lifting for the exposure.
Understanding the internal light meter of your camera is a skill you need to learn so you can master the ability of shooting your camera in manual mode.
The Purpose of the Light Meter
The light meter is a visual gage to tell you if your current settings (fstop, shutter speed and iso) will give you a capture that is over or under exposed. Or, if you have dialed in your settings, it will tell you that your exposure will be spot on.
Canon cameras will show you a range of -3 to +3 on the digital gage. In the middle of gage is 0, which would be the ideal exposure.
However, 0 represents 18 percent gray, and if there are a lot of dark tones or light tones in your frame, the meter may not give you a good exposure.
You may need to half-press the shutter button for the light meter and other settings to display along the bottom of the viewfinder.
The same technology that displays the meter reading also controls the camera settings if you are using one of the camera’s auto exposure modes.
The camera’s technology looks at all the zones in the frame and attempts to average them all out to 18 percent gray.
The frame is split into zones, on a Canon 5D MkIII it’s 63 zones. The camera will calculate the overall average light level based on the light and dark tones in each zone, and choose the exposure and show a meter reading based on that calculation.
Metering Modes
Depending on what metering mode you have selected, the light meter may look at all the zones in the frame, the center of the frame or a partial, spot meter.
This is how Canon explains its metering modes:
Evaluative: This is an all-around metering mode suited for portraits and even backlit subjects. The camera sets the exposure automatically to suit the scene.
Partial Metering: Effective when the background is much brighter than the subject due to backlighting, etc. This a mix between Spot and Center Weighted.
Spot Metering: This is for metering a specific part of the subject or scene. This metering mode is for advanced users.
Center-weighted average metering: The metering is weighted at the center and then averaged for the entire scene. This metering mode is for advanced users.
Nikon cameras have three metering modes.
Matrix, which is the same as Canon’s Evaluative, center-weighted and spot.
Zone, Matrix (Nikon) and Evaluative (Canon), Metering is the default metering mode of nearly every digital camera. It works great when there is even lighting in the frame. You should leave the metering mode on this most of the time.
Use the other metering modes in specific situations when the Zone Mode does not give you a good result.
The spot mode calculates the exposure, or meter reading if you are in manual mode, from less than 3 percent of the frame. The center-weighted mode uses 10-15 percent of the frame to make its calculations.
You can easily change the metering mode by pressing a button on the camera that has an icon that looks like the the zone (Matrix for Nikon and Evaluative for Canon) meter icon. Press the button then use one of the dials to change the metering mode. It’s the front dial for my Canon cameras and the back scroll wheel for my Nikon. Also, the Nikon requires me to hold down the button while I roll the dial on the back of the camera.
If you are shooting in manual mode, I’d leave the camera in the zone metering mode. The camera’s metering calculations do not set the camera exposure in manual mode, you do.
While you are shooting in manual mode, you should set up your LCD to display the histogram when you review images.
Adjust your exposure based on the histogram of your last capture to dial in the correct exposure for any given scene.
Last word on your light meter
You should be aware that the light meter will only show your settings as being over- or under-exposed if you have the camera set to manual mode. If you are in the Aperture Priority of Shutter Priority modes, the light meter will show you to be at 0, because the camera is changing the settings to keep the light meter at 0.
On a Canon Aperture Priority is AV mode while on a Nikon it is A mode. Canon’s Shutter Priority if TV mode, while on a Nikon it is S mode.
Also be aware that on the Canon cameras, if the light is more than 3 fstops over or under exposed, the the mark that shows where the exposure is goes completely off the gage. However, an arrow then appears at that end of the gage to show exposure is now more than 3 fstops over or under exposed.
My Nikon D500 has a light meter that only shows 2 fstops on either side of middle exposure. However, it will the gage bars all the way up to 2 fstops even if it is 3 or 4 fstops off.
Below are what the light meter looks like in a Canon 5D Mark III and a Nikon D500.
If the meter bars don’t point to 0, you can make adjustments to the fstop, shutter speed or ISO to correct the exposure.
Read and watch our tutorial on shooting in manual mode to learn more about manually changing your exposure.
