Beginner photographers quickly realize that automatic exposure (aperture priority, shutter priority, program mode) has limitations. Under some lighting conditions, additional techniques (exposure lock, exposure compensation) are needed to get the right exposure.
Fully manual exposure (also called metered manual) is actually simpler and faster than the automatic modes, in many cases. Here's how to use manual exposure on a DSLR.
A Personal Experience with Manual and Automatic Exposure Modes
I remember starting out over twenty years ago with a Yashica FX3 film SLR. Exposure was fully manual. You adjusted the shutter speed and aperture by turning mechanical dials, until a green LED lit up, telling you that the camera's light meter thought that the exposure was correct.
A few years later, I upgraded to an autofocus Nikon F801s. It was still a film camera, but had the aperture priority, shutter priority, and program mode of today's digital SLRs.
I enjoyed the automatic exposure at first, but often found myself going back to manual exposure mode. It was surprisingly easier and faster than automatic. My next camera was a Nikon FM2, a fully manual SLR, like the FX3.
The Problem With Automatic Exposure
Automatic exposure would be a good mode to use, if it worked all the time. Unfortunately, it often isn't accurate.
Under uneven lighting conditions such as backlighting (bright light behind the subject), the camera will under-expose or over-expose, resulting in a photo that is too dark or too bright. The remedy is to use exposure lock: pointing the camera at the ground and locking the exposure, then recomposing (pointing the camera back at the subject) and taking the photo.
Another problem is that the camera assumes that everything is gray. Very white (snow, white clothes) and very dark (black suits) objects confuse it. Photographers need to set plus/minus exposure compensation to cater for these situations. Different amounts of compensation are needed, depending on the brightness of the object, and how large it is (a black shirt will be partially offset by a pale face).
It's also easy to forget to reset the compensation back to zero, causing problems for subsequent photos.
"Smart" metering modes (matrix on Nikon, pattern/evaluative on Canon) attempt to detect and correct for these situations, but sometimes fail. An automatic system that can't be relied on, isn't very useful.
Photographers are often confused as to when to use exposure lock and when to use exposure compensation. One common mistake is to use exposure compensation, instead of exposure lock, for backlight situations. This works but needs some trial and error. The reason is that depending on the backlight, different amounts of compensation are needed.
Things get even more complicated when both exposure lock and compensation are used at the same time. Let's say the photographer wants to photograph a backlit subject, and he wants the subject to be a bit in shadow, to look natural. He dials in minus one (-1) exposure compensation, and then meters off the ground and locks the exposure - quite a lot of work for an "automatic" camera.
How to Use Manual Exposure Mode
The camera is set to manual exposure mode, by turning the mode dial to Manual or "M" on Canon and Nikon cameras. Shutter speed is set by turning the control wheel. Aperture is set by turning the second control wheel. For cameras with only one control wheel, press the "+/-" button and turn the control wheel, to set the aperture. This works for both Canon and Nikon (Canon helpfully marks the button "+/-" and Av).
Manual exposure uses the same metering system (center weighted or spot) used by the aperture priority, shutter priority and program modes. The difference is that the photographer manually adjusts aperture, shutter speed and ISO until the exposure meter is zeroed.
In manual mode, most cameras have an LCD bar graph that shows the current exposure (over, under, correct) to plus/minus two or three stops. The graph is either in the viewfinder or on the rear LCD screen. If the photographer simply zeros the meter, the exposure will be the same as with one of the automatic modes.
Exposure Lock Using Manual Exposure
Let's take the backlight situation again. The photographer meters off the ground. But instead of having to keep his finger on the exposure lock button, once he sets the exposure in manual mode, the exposure is automatically locked.
This means that he can take photos without worrying about his finger slipping and releasing the exposure lock, especially if multiple photos are taken.
On some cameras, it's possible to set the exposure lock button (for automatic exposure) to maintain the lock without keeping your finger on the button:
- Press once to lock exposure.
- Press again to release exposure lock.
The problem with this is that it is possible to forget to release the lock, ruining subsequent photos.
Exposure Compensation Using Manual Exposure
For exposure compensation in manual mode, the photographer adjusts the settings as normal. The difference is that instead of zeroing the exposure meter, he sets it to whichever plus/minus setting on the exposure meter bar graph that he chooses.
For the next exposure, he can use the same setting or manually set the exposure again. There's no need to remember to reset a separate exposure compensation setting.
If he wants to compensate beyond what the meter shows, he simply counts the click stops himself. Let's say that the meter only shows up to plus/minus two stops, and for a particular scene the meter is zeroed at a shutter speed of 1/30 seconds. To under-expose four stops, the photographer manually counts four stops from 1/30, which is 1/60, 1/125, 1/250, 1/500.
This is more flexible than conventional exposure compensation, where you can't compensate beyond the camera's fixed limit, say plus/minus three stops.
Combined Exposure Lock and Compensation Using Manual Exposure
Going back to the earlier example of backlighting with exposure compensation, how would it work with manual exposure mode?
The photographer would point the camera at the ground, and set the exposure so that the exposure meter reads minus one. That's it. Exposure compensation and lock in one step.
Multiple Exposure Locks With Manual Exposure
Let's say the photographer is at a sports match. He notices that the light is brighter in the center of the field, darker at the side. He can't use full automatic exposure because one team wears white and the other team wears black, which throws off the meter in different ways. (Exposure compensation wouldn't work. A different mix of players will require different compensation, depending on whether there were more black shirts, or more white shirts in the frame.)
He could use the spot meter and exposure lock on a player's face or on the field, but this is slow and uncertain (his finger could slip and release the lock, and he needs to recompose for proper framing after locking the exposure).
With manual mode, he meters off the field and finds out that the center of the field is two stops brighter than the sides. All he needs to do is set the exposure for the center of the field, then click the control wheel to increase exposure two stops when the action moves to the edge of the field, then click two stops back when the action returns to the center. He doesn't even need to look at the light meter. Quick and simple. He can also put the camera down at any time to rest his hands, without losing the settings.
The same technique applies for photographing in a large room with different lighting conditions, with women wearing white gowns and men wearing dark suits, throwing off the light meter in different ways.
Best Default Manual Exposure Settings
One difficulty with manual exposure is knowing where to start. With three settings (aperture, shutter speed, ISO) to change, which combination of settings should you use for different situations?
Luckily, there aren't that many different lighting situations. The two main ones are low light (indoors, night) and bright sunlight (outdoors, day).
- In low light, set maximum aperture (f3.5 on consumer zooms), then adjust ISO to get at least 1/30 or 1/60 seconds shutter speed. Alternatively, set maximum aperture and ISO 1600, then adjust shutter speed. This is faster but results in more noise as ISO 1600 is used even if a slower ISO is practical.
- In bright sunlight, set f5.6 or f8 aperture and ISO 100, then adjust shutter speed.
Few situations are in-between. If it's not bright sunlight, use the low light settings.
Using Full Stops for Manual Exposure
It's easier to use manual exposure, if only full stops are considered:
- f4, f5.6, f8, etc for aperture
- 1/15, 1/30, 1/60, 1/125, etc for shutter speeds
- 100, 200, 400, 800, etc for ISO
Using full stops means that the photo will at most, be over or under exposed by half a stop (if it is over exposed 9/10 stops, reduce the exposure one stop to get 1/10 stop under exposure). A half stop difference either way, isn't going to matter much. Unfortunately most DSLRs default to 1/3 stop steps (you need to click the control dial three times to change one stop), which only confuses photographers and slows down manual control. The camera can be switched to 1/2 stop steps, but it's revealing that it's usually only the professional DSLR models that can be switched to full stop steps (they also have two control dials: one for shutter speed and one for aperture).
When to Use Manual Exposure
Manual exposure isn't as difficult or useless as many might think. It's actually easier and faster under tricky lighting conditions such as backlight, night, and uneven lighting, any situation that confuses the light meter.
With the right approximate settings for the situation (low light, bright sunlight), it is possible to set the correct exposure within a few seconds by changing shutter speed and zeroing the light meter. This can be faster than auto exposure, if exposure lock or compensation needs to be used.
Manual mode is a good mode for beginners. It's easier to understand than the many automatic exposure modes (aperture priority, shutter priority, program mode, auto ISO) and compensations (exposure lock, exposure compensation) needed in automatic mode. A good understanding of manual exposure technique, helps photographers understand the quirks of automatic exposure. Starting with automatic exposure, can confuse beginners.
Automatic exposure can be confusing because there is no stable exposure base. Pointing the camera at different parts of the scene can change the automatic exposure, frustrating attempts to set exposure compensation. In manual mode, the exposure doesn't change until the photographer changes it. He can trial-and-error at leisure, looking at the LCD screen for instant playback.
With manual mode, photographers are also more aware of the camera's settings at all times, and are better able to develop their own judgment of the characteristics of each setting (ISO noise, depth of field, motion blur). This allows them to decide which trade-offs to make, when setting the exposure.
Yuen Kit Mun - Kit Mun is a self-confessed information junkie, reading an average of a book a week over the past two decades. His growing Internet ...
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