When scanning an object in 3D, it is important to determine if the hardware configuration is suited for the size of the object. For optical 3D scanners including white light 3D scanners, the camera and projector lenses determine a scanner’s field of view. Field of view (FOV) is the observable area that an optical instrument is able to capture from a specific distance. The most common focal lengths for camera lenses are 9mm, 12.5mm, 16mm, and 25mm lenses.
The field of view for 3D scanner configurations depends on the following factors:
- camera lens(es) being used
- lens on the projector
- distance between the 3D scanner and the object.
At the same distance a lens with a small focal length (mm) allows you to see more of the scene whereas one with a large focal length sees less of the scene but gives more detail.
You will need to provide:
- Focal length: The distance from the camera sensor to the lens, expressed in mm.
- Distance to the object: How far the lens is from the object.
- Image sensor: Equipment that converts an optical image to an electric signal. At 3D3 Solutions, most of our 3D scanners use image sensors that are 1/2" or 1/3”.
To determine your projector’s field of view please use this calculator: http://www.projectorcentral.com/projection-calculator-pro.cfm
You want to make sure the FOV coverage from your camera lens matches the FOV coverage on your projector from any particular distance. The projector lens generally doesn’t vary too much from model to model.
Here are some general setups that we use in our 3D scanning lab:
- 9mm lens: Scans half a person from approximately 1.5 meters away from the scanner.
- 12.5mm lens: Scans human faces from approximately 75 cm away from the scanner.
- 16mm lens: Scans small objects such as a computer mouse
It might appear that it would be better to use a lens with a smaller focal length. However, there is an inverse relationship between focal length and lens distortion. For example, the smaller the focal length (mm), the larger the distortion you tend to get when 3D scanning an object. All lenses have a certain amount of distortion that is unavoidable. Even though HDI 3D Scanner Software, FlexScan3D, compensates for lens distortion you do want to minimize the starting amount.
While zoom lenses provide more flexibility, they also have a tendency to create more distortion and are more expensive than non-zoom lenses. We recommend using non-zoom lenses.
If you purchase your own lenses for your 3D scanner, another factor to consider is each lens has an effective focal range. Focal range is the distance from a lens to its focus. Some are set to focus on objects from 1 meter to 2 meters, while others are set to focus from 1cm to 10cm. Most scanning projects require a focal range of 5cm to approximately 1.5 meters but experimenting with different settings is critical to determine the desired field of view for your particular application.
This blog post was previously posted on Wed, May 25, 2011 on 3D3 Solutions blog. LMI Technologies acquired 3D3 Solutions on May 1, 2013.
Posted by Thomas Tong