Manual mode and Auto ISO

Learning goal

You will be able to take exposure fully into your own hands by choosing the three exposure settings together in M mode. You will read the exposure scale in the viewfinder or on the screen and arrange the settings by it, explain why manual mode gives the most consistent result when the light is constant, combine manual mode with Auto ISO to keep the aperture and time in your hands while leaving brightness to the camera, set an upper limit for ISO in this combination, and record the faces of people with different skins in the same tone from frame to frame under constant light.

The question

To many people, manual mode looks like an exam. When you turn the dial to M, all three settings pass into your responsibility at once; it feels as if one wrong move will make the photo come out either pure white or pitch black. That is why many photographers stay away from this letter for years and think of manual mode as a room only experts can enter.

Is manual mode really hard? In fact, everything you have learned in this module is the key to this room. You know every corner of the triangle and can make trade-offs between the corners in stops. The camera helps you in manual mode too: it shows you with a scale which way you need to go. In this lesson we will talk about how manual mode works, in which moments it is the best choice, and why it turns into an everyday tool when combined with Auto ISO.

Context

The top step of the staircase in Lesson 3.9 was M mode: you choose both the aperture and the shutter speed. That day this step looked far away. In the lessons since, you have learned the light budget, the costs of the three settings and the idea of priority. In A and S modes you chose one setting, left the other to the camera and watched the value the camera chose. In manual mode only one thing is left to watch: the difference between the brightness the camera measures and the brightness you have set.

Auto ISO, on the other hand, is a bridge between manual mode and the automatic modes. On many cameras, while in M mode, you can leave ISO on auto. That way you choose the aperture and the time, that is sharpness and movement; the camera sets ISO to hit the brightness. Phones' pro modes have a similar arrangement: you can set the time by hand and leave ISO on auto. This lesson shows in which moments to use these two paths, full manual and manual with Auto ISO.

Simple explanation

How do you read the exposure scale?

In manual mode, a small scale appears under the viewfinder or at one edge of the screen: the exposure level indicator. In the middle there is zero, and on both sides plus and minus numbers; on most cameras each mark is a third of a stop. A marker moving above or below the scale shows where the settings you chose stand relative to the brightness the camera measured. If the marker is at zero, you are at the brightness the camera suggests; on the plus side the photo will come out brighter, and on the minus side darker.

There is a simple order to working in manual mode. First choose a setting according to the scene's priority: the aperture if sharpness matters, the time if movement matters. Then bring the second setting to a safe value. Finally set ISO so as to bring the marker on the scale to where you want it. Where you want it doesn't always have to be zero: in snow you can go to the plus side on purpose, and in a dark scene to the minus side. The scale isn't an order but a compass; the decision is still yours. After a few tries, this order turns into a habit of a few seconds.

Why does manual mode give the most consistent result?

In automatic and semi-automatic modes, the camera measures the scene again in every frame. When a white shirt enters the frame it darkens the photo; when a dark curtain enters, it brightens it. Even though the light stays the same, the brightness of the photos shifts from frame to frame. In manual mode, on the other hand, once you set the settings, every frame comes out at the same brightness as long as the light doesn't change. Whatever enters the frame, if the light falling on the subject is the same, the subject is recorded in the same tone.

That is why manual mode is the mode for constant light. A show under stage lights, a night street lit by streetlights, a room lit by a single window, shoots with flash, and a panorama series that will be stitched together are where manual mode is most useful. When photographing a series of portraits, manual mode also makes all the frames look the same tone and suited to each other. If the light is changing fast, for example if you are going in and out on a cloudy day, in manual mode you need to set the settings again at every change; then Auto ISO or A and S modes are more practical.

How does Auto ISO make manual mode easier?

When you leave ISO on auto in M mode, you choose the aperture and the time, and the camera sets ISO to hit the brightness. This is especially useful in situations where the light changes but sharpness and movement matter: going out from the hall to the garden at a wedding, as the lights change on a stage, or as clouds pass at a match. The aperture and the time stay as you want; only ISO changes.

A setting not to overlook in this combination is ISO's upper limit: on many cameras you can set a maximum auto ISO, the highest value Auto ISO can go up to. If you have found the grain limit you can accept on your own camera, put the upper limit there. Compensation works in this arrangement too: on many cameras, with Auto ISO on in M mode, compensation also works and adjusts brightness by shifting ISO. When the camera hits the upper limit, the photo starts to darken and the marker on the scale slides to the minus side; this tells you that the light has run out and you need to rethink the time or the aperture.

How is skin kept under constant light?

The consistency of manual mode is especially valuable when photographing different skins. In automatic modes the camera looks at the average of the scene in every frame; when a dark-skinned person steps in front of a white wall, their face stays in darkness, and when a light-skinned person steps in front of a dark curtain, their face glows. Even though the light is the same, the tone of the face changes with the background. In manual mode, on the other hand, once you set the exposure by the face, that face is recorded in the same tone whatever the background.

The way to set this up is simple. Take a test frame in the scene's light and zoom in on the face. If detail can be made out on the shaded cheek of dark skin and no bright patches form on the forehead and nose of light skin, your settings are right. If there are several people with different skins in the frame, look with test frames for a shared setting that leaves detail in each one's shadow and bright areas. Then leave the settings fixed; as the people move and the backgrounds change, the tone of the faces stays in place. When the light changes, take a new test frame and set the settings again.

Visual evidence

You are photographing a school play from in front of the stage. The stage is dark, and the children are acting under a single fixed spotlight. First you shoot in A mode. When a dark-skinned boy in a white costume steps under the spotlight, the camera tries to make up for the darkness of the stage and the costume blows out pure white. When a light-skinned girl in a black costume steps under it, her face glows too much. The same spotlight, the same light; but a different brightness in every frame.

You turn the dial to M, fix the opening at f/2.8 and the time at 1/250, and take a test frame under the spotlight. At ISO 1600 the boy's face, the sparkle in his eyes and the folds of his costume can be made out; the costume doesn't blow out. You leave the settings fixed. When the girl steps under the spotlight, her face is in its natural tone too; both her own black costume and the boy's white costume are in their real tones. When the play ends and the children come out into the foyer, where the lights change all the time, you turn on Auto ISO and set the upper limit to 6400; the aperture and time are still yours, the camera only shifts ISO. Full manual for the constant light on stage, manual with Auto ISO for the changing light in the foyer.

Common mistakes

Summary

In manual mode all three settings are in your hands; the camera shows with an exposure scale where the brightness you chose stands relative to what it measured, and this scale isn't an order but a compass. When the light is constant, manual mode gives the most consistent result, because whatever enters the frame the subject's tone doesn't change; this consistency makes it easier to record faces with different skins in the same tone from frame to frame. When the light changes, Auto ISO leaves the aperture and time in your hands and hits the brightness with ISO; in this combination you need to set an ISO upper limit and watch for the marker on the scale sliding to the minus side.

Mini assignment

In this assignment you will try manual mode in two different lights on the same evening.

1. Find a place with constant light, which could be a corner lit by a desk lamp, and set the aperture, time and ISO in M mode by reading the scale.
2. With the same settings, take three frames, putting first a white and then a dark object into the frame, and see whether the subject's tone changes.
3. Move to a place where the light changes, for example a spot you go back and forth through between a window and the room, turn on Auto ISO in M mode and set an upper limit.
4. In constant light, photograph two people with different skins, setting the exposure by the faces with test frames and without changing the settings.

Check yourself

• Can you read the marker on the scale and quickly find which setting to turn in which direction?
• In the frames taken with fixed settings, did the subject's tone stay the same despite the objects entering the frame?
• Did both faces come out, without changing the settings, with detail in the shadows and without patches in the bright areas?

Glossary

Mini quiz

1. If the marker on the scale is at plus two in manual mode, what does that mean?

• A) The photo will come out two stops brighter than the camera suggests
• B) The photo will come out two stops darker
• C) ISO has doubled
• D) The aperture has been stopped down two stops

2. In which situation does manual mode give the most consistent result?

• A) A day when clouds pass quickly
• B) A scene where the light stays constant
• C) A shoot going back and forth all the time between a window and a room
• D) A concert where the light changes every second

3. In M mode with Auto ISO on, what does the camera set?

• A) The aperture
• B) The shutter speed
• C) The white balance
• D) ISO

4. To record dark- and light-skinned children in the same tone from frame to frame under a constant stage light, what do you do?

• A) Shoot in A mode and let the camera measure again in every frame
• B) Change the compensation at random in every frame
• C) Set the exposure by the faces with test frames and leave the manual settings fixed
• D) Turn on Auto ISO without an upper limit

Answers

1. A — The scale compares the chosen settings with the brightness the camera measured; plus two means a result two stops brighter.
2. B — Manual settings stay fixed; if the light is constant too, the subject is recorded in the same tone in every frame, whatever enters the frame.
3. D — The aperture and the time stay with the photographer; the camera shifts only ISO to hit the brightness.
4. C — Under constant light, fixed settings keep the tone of the faces even when the background changes; test frames help find the point that keeps both faces.

Summary card

• In M mode all three settings are yours; the scale is a compass, not an order.
• The order: choose the priority, bring the second setting to a safe place, place the scale with ISO.
• If the light is constant, manual is the most consistent: even when the background changes, the subject stays the same tone.
• If the light changes, M + Auto ISO: sharpness and movement with you, brightness with ISO.
• Put an upper limit on Auto ISO; set faces once with a test frame, then leave the settings fixed.

Bridge to the next lesson

Now you know all the modes from full auto to full manual: A, S, M and manual with Auto ISO. But facing a portrait, a match or a landscape, which one will you choose? The next lesson gathers all these options at the end of the module into a single practical decision table: whatever you want to control, choose that mode.