Shutter Priority Mode

Motion blur is a common problem in aerial photogrammetry. It's typically due to a slower shutter speed while the craft is flying quickly. To avoid the motion blur effect, we can set the camera into shutter priority mode. 

What does it do?

Shutter Priority mode allows the user to specify the camera's shutter speed while the aperture and ISO adjust automatically. This lets the camera achieve the correct exposure.

Common platforms will default to an Auto exposure mode. This mode works well for users who want to take a few pictures or videos without much effort, but it is not as well suited for photogrammetry. 

Auto will typically try to keep the aperture in its optimal value range. 

For example, this may be good for a stationary photo but bad when the shutter speed has been reduced to 1/100 to achieve it. All of the detail in your images become blurred. This blur has a major impact on the final model's accuracy and orthomosaic clarity. In some cases, ground control points can become obscured to the point that they are unusable.

There are other components to motion blur, but the main factors you need to be aware of are how fast the craft is flying and how fast the images are being taken.

Examples:

Flying at 10 m/s

1/100

1/500

1/1000

Propeller uploader—motion blur warning

Propeller's uploader will check image metadata before uploading begins and flag images with increased motion blur. 

If you receive a warning, please check your images for motion blur. If it's severe, you must fly that area again with updated settings. 

We will flag images with over 20mm of motion blur present. However, lower is still better.

How do I set up Shutter Priority mode?

Setting up Shutter Priority mode will depend on the system you are using. The mode is typically denoted with a capital (S).

Limitations and further explanation

Taking an image as fast as possible is not always the best solution. When using Shutter Priority mode, we are locking one of the three methods available to control the image's exposure. The other two components of the equation (Aperture and ISO (for our purposes at least)) will need to work around the limits that we've set.

If the shutter speed is too fast for the lighting conditions, we may see the aperture fully open and the ISO, which can be seen as a sensor gain, increase considerably. 

The higher the ISO, the more sensor noise will be present in the final images. F

In winter or low-light environments, you may need to reduce your flight and shutter speeds to maintain the same low-motion blur as the brighter environments can achieve while flying faster.

Does the Aperture have an impact on image quality?

Yes, it does, and it has a sweet spot where the camera can take the sharpest images.

The sweet spot will depend on the system you are using, but a rule of thumb that can be used is to have the aperture closed down approximately two and a half stops. 

If you are unsure, it is well worth looking up your camera and lens to determine where this sweet spot lies and see the performance when the aperture is fully open.