I'm using Sony A7R II with 28mm lens and I'm curious why my focal length change slightly? it's a prime lens and manufacturer spec says it's 28mm and the aero-triangulation optimized the focal length in the range of 27.13mm - 27.20mm for different photogroups. Should it not always be 28mm? if my focal length is incorrect, does that error propagate to the accuracy of the result?
Thank you
Chan
It is just one of parameters which CC adjust to get the results right. It should be near the real value but may not be exact. If you will lock(keep camera calibration) the focal length it may even produce worse results. To get exact you would have to measure sensor size to tenth of milimeter. If you like to have near 28mm then adjust sensor size slighlty as sometimes it is provided as sensor pixel size multiplied with resolution so is not exact.
thanks for the answer. it helps. if I use calibrated metric camera say for example phase one or vexcel ultra cam, will the discrepancy between optimized and manufacturer specification match more closely?
Maybe but I would not take it too directly you have to leave room for adjustments. CC doesn't calculate all camera metrics and parameters so slight deviation is acceptable.
Do you know sensor size accurately for this camera? What sensor it uses? If not then how to trust manufacturer specification if it doesn't provide exact part number for sensor matrix and keeps it as trade secret.