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Trouble report 38

Focal length fine tuning does not work for 24-bit images

Versions affected

V1.0 - V1.6.


There is a major problem with the Fine tune option on the Focal length dialog for 24-bit images. This problem prevents focal length fine tuning from working for 24-bit images. It does not effect 45-bit images.

There is a minor problem affecting both 24-bit and 45-bit images. This problem may cause the fine tuning to be slightly less accurate.


If your images have sufficient overlap, you can use 45-bit mode to calculate the focal length:

  1. Select a representative pair of images from your project.
  2. Create a new project using only the two images chosen in step 1.
  3. In this new project, open the Project properties dialog (File menu) and select "Use 45-bit pixels".
  4. Enter your initial value for focal length on the Focal length dialog (Tools menu).
  5. Stitch the two images.
  6. Select "Fine tune" on the Focal length dialog.
  7. Transfer the focal length value that results from fine tuning to the Focal length dialog in the original project.

If you have less than about 25% overlap it may be insufficient to automatically calculate focal length.  In this case, you can follow this manual procedure:

  1. Start with an initial estimate of the focal length.
  2. Select a representative pair of images from your project and stitch them into a panorama.
  3. Analyze the overlap region to decide whether to increase or decrease the focal length.   By looking at way lines in the picture cross you can decide whether to increase or decrease the focal length.  If lines do not cross, the focal length is perfect.

    Increase focal length:
    increase.jpg (6251 bytes)

    Decrease focal length:
    decrease.jpg (6948 bytes)

  4. Adjust the focal length and restitch the panorama.
  5. Repeat steps 1 through 4 with smaller and smaller adjustments until you are satisfied.


Both problems are fixed in V2.0.  The manual procedure may still be necessary when the overlap is too small.

Revised: June 14, 2004

 1999-2005 Smoky City Design, LLC and John Strait