In what practical applications is the position of the sensor plane relevant?

Question

Most DSLRs have a small sign showing the precise position of the sensor plane.

In what practical photographic applications would one need to use this information?

I know that focus distances are measured from the sensor plane (e.g. the minimum focus distance specification of lenses).

Answer 1

This is key to measure the exact distance to the objects in a shot.

Especially for tasks in visual effects like:

• reconstructing real world cameras of an image or a video via match moving techniques to check the calculation of the solver or make sure the distances are correct
• shooting panoramas or simply extend images to make sure nodal point is correct so that objects are always captured with the same size

Further scenarios:

• building a camera rig with more than one camera to make sure you can easily stitch the images
• building a camera microscope to calculate the required lens to get the desired magnification

Answer 2

In addition to the excellent answer by Poor, I can add from my own experience in astrophotography. When you want to attach your camera to a telescope to capture photos of deep sky objects, you'll need to know the exact focal point of the telescope objective. In a newtonian reflector, for example, the focal point/plane of the primary mirror falls somewhere in the focusing tube, and to get the image on the camera sensor, you'll attach the camera to the focuser using T-adapter and T-rings, and adjust it so that the sensor plane lies at the focal point of the primary mirror. Knowing the exact position of the sensor plane makes life much easier when you're trying to focus your telescope.

Answer 3

For macro photography it is also very useful to know the exact distance from the sensor to the object. That allows you to measure sizes from the photos taken in a very precise way.