Camera tracking - Focal length: Use device's or smallest track error?

Most of what I do in Blender is camera tracking. But there’s an issue I am still confused about, and I’d like to know which is the right way.

I film using my Samsung Galaxy S3, which has a focal length of 37mm. Therefore that is the focal length I should use for solving the camera motion. However, using 32mm gives a smaller track error, and also feels a bit better to me.

Is it a strict rule that the focal length of the device the video was taken with must be used for the camera in the Blender scene? Or should I go with the focal length that yields the smallest track error?

No info on this? So far I’m going with the focal length that yields the least track error. Would still like to know if I’m doing right and what your recommendations are however.

the fl that you use for tracking depends on many different factors…

what sw are you using? 37mm seems to be a 35mm equivalent fl… is the sw set to 36mm?

what mode are you in? 1080p will probably have a longer fl than 720p in the s3

which refine options are you using to get the lower error and fl?

The tracker can give you a ‘false’ low solve error sometimes with the wrong fl, k1, k2 values… if you are lucky, it won’t matter but you might notice perspective differences when you composit the 3d elements into your original footage… in that case you are better off with a slightly larger error and correct fl.

if you would be willing to spend a few minutes to set up and shoot a quick calibration shot, I should be able to give you an accurate 35mm equiv fl… pm me

You could try using the Blam add-on to see what focal length it comes up with (it assumes a 35mm sensor). Does your camera phone have a fixed focal length, or can you zoom in at all?

Steve S