Hi
 
I have a question about focal length with cameras.
 
I have a Nikon D100, with a 17-35mm lens.  For my photogrammetry work, I leave it locked on 17mm.  All my pictures are taken at this focal length - just to make the photogrammetry stage go a lot smoother.
 
When I import these into ImageModeller, and start working with them - I set the camera focal length to 17 - and change the mode to constant (since I am sure, it isn't going to be exactly 17mm).
 
After going through and calibrating my scene, IM calculates the focal length to actually be 22mm.  If I change it to "kown" and set it back to 17 - it wont go through the calibration correctly.
 
Further to this, I have Photomodeller - and I ran through their steps to calibrate your camera, prior to using it in Photomodeller.  This came out with wildly different results to those found in Imagemodeller - it worked out that the focal length was 17.098mm - (this is from me telling it nothing, just photographing their test grid).
 
Right now I am a little concerned between these focal-length differences... I know it is a 17mm lens, Photomodeller calibrates my camera to 17.098mm - why is imagemodeller saying that it is 22mm???

Hello,
 
  This is probably due to the "high" distortion related to short focal lenght.
While calibrating, did you let distortion value to constant ?
 
Could you send 3 or 4 images with that focal that calibrate in IM at support@realviz.com ?
 
You can do the same procedure (as in PM) for calibrating your "internal" camera parameters (Copy/paste of an older post) :
 

 
Best regards,
 
Stef