From BlenderWiki
Real world focal length
To match real footage in 3D, whether it is live action or a still, the one common denominator is the "field of view" (fov) also known as "angle of view". This value is in degrees and by itself not very intuitive to use directly, when a few degrees off can make a big difference. Instead we refer to the focal length ('lens' in Blender) as the unit of measurement for the perspective. Ideally the focal length is also known for the footage we are working on, either by being told by the cameraman or by looking in the EXIF data, whereas the fov is practically never known.
The focal length and fov are interconnected, so changing one changes the other, according to a mathematical formula using a third variable: the camera sensor size. Without this value it does not matter if we know the focal length for some footage, as the same focal length can result in a different fov, just as the same fov can be shared by different focal lengths. It is crucial to know the camera sensor size to ensure a correct match.
 | Location data |
| When shooting on set bring a measuring tape! |
Blender camera properties
http://www.pasteall.org/pic/show.php?id=12795
Lens
- Focal Length
- This is the real world focal length in millimeters.
- Field of View
- Displays the fov in degrees. Option to show either the Horizontal or Vertical value. This is primarily for information, but important for importers/exporters.
Camera
- Camera Presets
- Small list of common camera sensor sizes, including the default Blender sensor size.
Notice
There exists a large number of sensor sizes, and even within a "standard" such as APS-C, sizes can vary between manufactures and models.
Beware of the "Crop factor"! It does not change the real focal length used. |
- Sensor Size
- X
- Width of sensor. Used to calculate the horizontal fov from the focal length.
- Y
- Height of sensor. Used to calculate the vertical fov from the focal length.
Display
- Sensor
- Displays the sensor size relative to the render resolution.
Todo
With apparent and immediate benefits already in having a meaningful focal length, and for correctly importing/exporting cameras in a mixed software pipeline, a few points needs to be taken in to consideration:
- The distance to focus calculation, where having an "infinite" focus and focusing on an object 1 meter away, changes the fov/focal length slightly for more precision/realism, is not implemented.
- Almost no DCC applications have this feature, and the question is how important it is to have in Blender, but it would be nice.
- Speaking of correct measurements in relation to the camera, with Cycles going for a more physically correct camera model, it is worth thinking about how the lens aperture/f-stop can relate to the real world, for setting DoF and bokeh more intuitively.
- Right now background images set to camera view are controlled by the render resolution and not the sensor size. This distorts the image when the image aspect and device aspect ratio are different. Optimally we would have control over the resolution gate, defining what is visible and how within the device aspect ratio. Instead of the "Sensor" display option we should have a "Render" display option.
- Basic example:
- http://www.pasteall.org/pic/show.php?id=12798
Links
Patch by Matt Ebb:
http://mke3.net/weblog/blender-sensor-sizes
Table of sensor sizes:
http://en.wikipedia.org/wiki/Image_sensor_format#Table_of_sensor_sizes
For a huge database over DSLR specifications look here:
http://www.dpreview.com/products
Example camera:
http://www.dpreview.com/products/sony/slrs/sony_dslra290
For film/video cameras most sensor specifications can be found with an online search.
Example RED:
http://www.jfi.net/RED/REDFormats3.pdf
