Estimation of focal length when using BLAM I am trying to understand how the BLAM addon works. In the Blender default scene I made an image of a cube with camera focal length 35mm. Then I created a new blend file and opened this image in the movie clip editor and did draw the lines requested for camera calibration with BLAM.



After BLAM camera calibration the focal length was set at 32.37. I really don't understand this (the image was made in blender with 35.0).
Blams accuracy depends on your line drawing accuracy. Maybe if you would repeat the cube line pixel to pixel it would calculate focal length correctly, but I bet there would still be some minor inaccuracy. As for the mesh reconstruction, even in introduction video is stated, that resulting object will probably not be perfect, so you should expect that. BLAM is not perfect, but certainly changes tens of minutes of tweaking into few minutes of tweaking, so it's not bad at all.