Forum

Author Topic: Camera Calibration - Focal Length  (Read 1923 times)

NickM

  • Newbie
  • *
  • Posts: 9
    • View Profile
Camera Calibration - Focal Length
« on: June 07, 2021, 10:56:31 PM »
Hello,

For the focal length within the camera calibration (Tools --> Camera Calibration) should the input value for this represent the focal length of my lens or the 35 mm equivalent focal length?

I.e. If I am taking photos with a 50 mm lens, should I have 50 mm for the focal length or should I have 80 mm (50 mm * 1.6; where 1.6 represents my crop factor)?

Thanks.

Paulo

  • Hero Member
  • *****
  • Posts: 748
    • View Profile
Re: Camera Calibration - Focal Length
« Reply #1 on: June 08, 2021, 12:11:05 AM »
NickM,

you should enter the real focal length not the 35 mm equivalent.

Following example shows case of Phantom4Pro camera that has a 8.8 mm focal length (about 24 mm in 35 mm equivalent) with a 1” Type sensor...
Best Regards,

Paul Pelletier

NickM

  • Newbie
  • *
  • Posts: 9
    • View Profile
Re: Camera Calibration - Focal Length
« Reply #2 on: June 08, 2021, 12:38:36 AM »
Thanks Paul,

Within the Photo Pane --> Details, does the "35 mm focal" column represent the 35 mm equivalent? Should Metashape be calculating this automatically based on EXIF data? When aligning photos mine remains blank.

Nick

Paulo

  • Hero Member
  • *****
  • Posts: 748
    • View Profile
Re: Camera Calibration - Focal Length
« Reply #3 on: June 08, 2021, 01:41:44 AM »
yes 35 mm focal represents the 35 mm equivalent focal length...

this is read from Exif data if present... in case of Phantom4Pro the exif data contains:
Quote
---- ExifIFD ----
Exposure Time                   : 1/400
F Number                        : 5.6
Exposure Program                : Program AE
ISO                             : 100
Exif Version                    : 0230
Date/Time Original              : 2020:03:03 12:03:49
Create Date                     : 2020:03:03 12:03:49
Components Configuration        : -, Cr, Cb, Y
Compressed Bits Per Pixel       : 3.130994232
Shutter Speed Value             : 1/400
Aperture Value                  : 5.6
Exposure Compensation           : 0
Max Aperture Value              : 2.8
Subject Distance                : 0 m
Metering Mode                   : Center-weighted average
Light Source                    : Daylight
Flash                           : No flash function
Focal Length                    : 8.8 mm
Flashpix Version                : 0010
Color Space                     : sRGB
Exif Image Width                : 5472
Exif Image Height               : 3648
Exposure Index                  : undef
File Source                     : Digital Camera
Scene Type                      : Directly photographed
Custom Rendered                 : Normal
Exposure Mode                   : Auto
White Balance                   : Manual
Digital Zoom Ratio              : undef
Focal Length In 35mm Format     : 24 mm
Scene Capture Type              : Standard
Gain Control                    : None
Contrast                        : Normal
Saturation                      : Normal
Sharpness                       : Normal
Subject Distance Range          : Unknown
Serial Number                   : 99cb05b9d3907adc8b429de0b2f2b9ec
Best Regards,

Paul Pelletier

NickM

  • Newbie
  • *
  • Posts: 9
    • View Profile
Re: Camera Calibration - Focal Length
« Reply #4 on: June 08, 2021, 02:08:23 AM »
Thanks again, was the Exif Data summary that you provided generated in Metashape?

Regards,

Nick

Paulo

  • Hero Member
  • *****
  • Posts: 748
    • View Profile
Re: Camera Calibration - Focal Length
« Reply #5 on: June 08, 2021, 07:47:57 AM »
The extrct shown was taken with ExifTool
Best Regards,

Paul Pelletier