How do I take calibration images for a long focal length lens?

The image fan method is used for capturing terestrial calibration imagery for open pit long focal length lenses (usually 200 mm+).

The terrestrial calibration scene should contain various depths to aid the camera calibration process. Try to incorporate a few benches on a curved pit wall in the image fan from each station to maximise the variation in depths. Limit the amount of sky or terrain which is parallel to the field of view as no relative only points will generate there. It’s a good idea to have accessible space for the four camera stations so they can be set up in a diamond shape configuration.

Image fan long focal length

Object Distance: For Station 1, stand at least 500 m away from the calibration scene. This means that the distance between the four camera stations should be 100 m separation using the 5:1 distance/base ratio.

Aim for 50% overlap between each adjacent image on a station fan, both horizontally and vertically between rows for the calibration project. It is most likely you will need to take at least a few rows of images from each station. 3DM Analyst Mine Mapping Suite can perform camera calibrations and has no image number restrictions per project. Expect to take 20 or more images per camera station, remember you need to cover a few benches for the total calibration scene from each station for a successful calibration.

The usual procedure applies for focussing for image fan capture, the first position of the fan uses AF (Automatic Focus) - the view should now look sharp looking the camera’s viewfinder. Next, switch back to MF (manual focus) to take all the photos using the same focus for all the camera stations (being careful not to bump the lens).

Camera Settings

  • Set aperture mode to Aperture Priority Av.

  • Select f/8 as aperture setting.

  • Set ISO to 100 (Canon cameras).

  • Set White Balance as AWB (Auto White Balance).

  • Set focus type in the lens as AF (Auto Focus), focus on a distant object and switch to MF (Manual Focus) to take the imagery.

  • Set Metering mode as Evaluate Metering.

  • Set Auto Image Rotation OFF.

  • Set image quality as fine.

Align the white arrow on the camera shuttle to the ‘200 mm’ engraving on the ADAM Technology open pit frame when using the 200 mm lens.

ADAM Technology offers a camera calibration service for calibration images taken using the above method. Please contact us for further pricing details at sales@adamtech.com.au