Shooting manual is like driving a stick shift; it can get you out of a lot of sticky situations, and gives you a better understanding of the underlying mechanics.
In simplest terms, to take a photo with manual exposure is to first determine the light level, set the camera to the appropriate combination of shutter speed and aperture for the required exposure, compose, focus, and release the shutter. Simple enough.
But what’s not so simple is balancing the four variables required to accomplish this; LV, ISO, Av and Tv.
LV or Light Value, is the intensity of the light you’re working with, and it’s the most important variable of all. It can be measured as the light reflected by the subject, or the light falling on the subject (incident). It can be measured by your camera, and also by a dedicated light meter. And believe it or not, it can also be measured by the human eye through experience. LV is measured in stops, which correspond to shutter speeds and f-stops.
ISO (also designated as ASA or DIN) represents the sensitivity of the film you’re using, or how the sensor is set to interpret the light. Sensor sensitivity does not change; when you set ISO on your camera, you’re instructing it to use a portion of the sensor’s maximum sensitivity. ISO is measured in stops, which correspond to shutter speeds and f-stops.
The combination of LV and ISO determine the EV, or exposure value. The EV changes in relationship to the ISO, but the LV does not. At ISO 100, EV is equal to LV. At ISO 200, the EV decreases by one stop. At ISO 50, the EV increases by one stop. Which brings us to Tv and Av, or shutter speeds and f-stops.
Tv or Time Value is represented by the shutter speed measured in fractions of a second. It’s one of the two components that make up EV.
Av or Aperture Value is represented by the size of the opening that allows light to enter the camera, measured in f-stops. It’s the second of the two components that make up EV.
The combination of Tv and Av determine the Exposure Value, and as one increases, the other decreases. Therefore, if EV14 is equal to 1/2000 @ f/5.6 @ ISO 200, then it’s also equal to 1/1000 @ f/8.0 and 1/4000 @ f/4.
So right about now you’re probably wondering why cameras don’t simply have an EV setting, which would simplify things a great deal. The reason is because with the right combination of shutter speed and aperture you can freeze action, isolate a subject from it’s surroundings, create motion blur, or reduce the need to focus.
Shooting manual requires that you know which combination of shutter speeds and apertures yield a given EV at a specific ISO. This information can be memorized, or referenced using an exposure table.
It also requires that you know the light level you’re working with as known from experience or obtained through a light meter.
Memorizing a table of Light Values is much easier than Exposure values, because there are only about 14 EV steps to worry about, but each can have as many as 10 combinations of shutter/aperture values.
You can train yourself to judge LV levels by eye by playing a little game. Memorize the table below, and carry a pocket light meter set to ISO100 with you wherever you go. As you encounter different lighting situations, try to guess the LV first, then measure it. After a while, you’ll be able to estimate LV by using a combination of the general conditions, and what your eyes are telling you.
| Exposure Value | Conditions |
| LV18 | Bright reflections off a sunlit object, such as the sea |
| LV17 | A white object in full sunlight |
| LV16 | Light gray object or skin in full sunlight |
| LV15 | Gray card in full sunlight |
| LV14 | Typical level for side-lit subjects in full daylight |
| LV13 | Typical shadow in a daylight scene; cloudy-bright days |
| LV12 | Bright overcast |
| LV11 | |
| LV10 | Dark, dreary overcast day |
| LV9 | |
| LV8 | |
| LV7 | Typical indoors; outdoors about ten minutes after sunset |
| LV6 | |
| LV5 | |
| LV4 | |
| LV3 | Brightly lit night street scenes |
| LV2 | Typical night street scenes |
| LV1 | Dark outdoor scenes at night |
| LV0 | Light level requiring an exposure of 1 sec @ f/1.0 @ ISO 100 |
| LV-1 | |
| LV-2 | |
| LV-3 | |
| LV-4 | |
| LV-5 | Scene lit by a full moon |
| LV-15 | Scene lit only by starlight |
If you memorize at least one ISO/LV/Tv/Av combo, you’ll be able to “count the clicks” to the correct exposure. For example, set your camera to ISO 200, f/5.6 @ 1/2000. This is the exposure for a sunny day at LV14. Now, moving indoors to a brightly lit room, the LV drops seven stops to LV7. Open up the aperture two stops to f/2.8, and bring the shutter speed down by five stops to 1/60, and you’re there.
If you want retain the wider depth of field afforded by the f5.6 aperture, adjust the ISO instead of the shutter speed. Setting your camera to ISO 800 gives you two stops. Bringing the shutter speed down to 1/60 gives you the other five, and you can keep the aperture at f/5.6.
If however you’ve got a fast f/1.4 lens, you can continue to shoot at ISO 200, but use a shutter speed of 1/125 which gives you a noise-free image with a narrower depth of field, and perhaps less edge sharpness.
All of this becomes second nature after shooting manual for a while, which makes it all the more easy to understand when you use your camera’s auto exposure system.
No comments:
Post a Comment