You are describing what we call in photo jargon “bracketing”. We choose our best guess at the correct exposure and then make a series of exposures. The idea is, we bracket the spot-on with one higher and one lower as to exposing energy. This can be accomplished by increasing / decreasing the working diameter of the cameras aperture. This can also be accomplished by increasing / decreasing the shutter speed. It is also possible to accomplish a bracket using both shutter speed and aperture.

The first question to be considered is the increment of change. Traditionally the photo industry has uses the magnitude of one “f-stop” as the principle increment. This is a doubling or halving of the exposing energy. Thus 1 f-stop is a 2X incremental change. To accomplish a three exposure series using shutter speed, the factor is 2x the base time – base time – 0.5x the base time. If the 2X increment is too course, you use a 1/2 stop increment which translates to a 150% of base time – base time – 50% of base time. If this increment is too course, than the 1/3 stop increment is next.

If you choose the use to use an aperture adjustment as opposed to shutter speed, we adjust the aperture in terms of an f-stop which is a ratio. This this focal length of the lens divided by the working aperture diameter. This method is used because the ratio is dimensionless. In other words, any lens functioning at a given f-number yields the same image brightness regardless of the dimensions of the lens. So a camera set to f/8 exposes a scene exactly the same as another camera set to f/8, even if the two cameras are different as to size or lens. To make a bracket based on a 2X change via f/number, the factor to use as the multiplier or divisors is the square root of 2 = 1.414. Thus: Base f/number x 1.4i2 – base f/number – base f/number x 0.707 (invers of 1.414).

To adjust the f/numbers in 1/2 stop increments the factor is the 4 root of 2 = 1.189 and is inverse 0.84. To adjust the f/numbers In 1/3 stop increments the factor is the 6 root of 2 = 1.122 and its inverse 0.89.

You are describing what we call in photo jargon “bracketing”. We choose our best guess at the correct exposure and then make a series of exposures. The idea is, we bracket the spot-on with one higher and one lower as to exposing energy. This can be accomplished by increasing / decreasing the working diameter of the cameras aperture. This can also be accomplished by increasing / decreasing the shutter speed. It is also possible to accomplish a bracket using both shutter speed and aperture.

The first question to be considered is the increment of change. Traditionally the photo industry has uses the magnitude of one “f-stop” as the principle increment. This is a doubling or halving of the exposing energy. Thus 1 f-stop is a 2X incremental change. To accomplish a three exposure series using shutter speed, the factor is 2x the base time – base time – 0.5x the base time. If the 2X increment is too course, you use a 1/2 stop increment which translates to a 150% of base time – base time – 50% of base time. If this increment is too course, than the 1/3 stop increment is next.

If you choose the use to use an aperture adjustment as opposed to shutter speed, we adjust the aperture in terms of an f-stop which is a ratio. This this focal length of the lens divided by the working aperture diameter. This method is used because the ratio is dimensionless. In other words, any lens functioning at a given f-number yields the same image brightness regardless of the dimensions of the lens. So a camera set to f/8 exposes a scene exactly the same as another camera set to f/8, even if the two cameras are different as to size or lens. To make a bracket based on a 2X change via f/number, the factor to use as the multiplier or divisors is the square root of 2 = 1.414. Thus: Base f/number x 0.707 (invers of sq. root 2) – base f/number – base f/number x 1.414).

To adjust the f/numbers in 1/2 stop increments the factor is the 4 root of 2 = 1.189 and its inverse 0.84. To adjust the f/numbers In 1/3 stop increments the factor is the 6 root of 2 = 1.122 and its inverse 0.89.