FOV calculation.
Rogier Wolff
I KNOW my camera rotates 7.2 degrees between shots. It might
occasionally vary between 7.1 and 7.3, but not much more.
Each column overlaps for almost 50% with the previous column.
This means that my FOV would be about 14 degrees.
However, from the exif info, hugin 2011.4 deduces about 10.2
degrees. I've taken the shots at 135mm, so my rule-of-thumb
calculation (divide 1800 by the focal length (*)), comes to 13.3
degrees FOV. That might be about right, but 10.2 is way too small.
The relevant Exif info is:
ExifTool Version Number : 8.60
File Name : DSC_6025.JPG
Camera Model Name : NIKON D80
Focal Length : 135.0 mm
Lens : 18-135mm f/3.5-5.6
Focus Distance : 0.47 m
Min Focal Length : 18.3 mm
Max Focal Length : 134.5 mm
Lens ID : AF-S DX Zoom-Nikkor 18-135mm f/3.5-5.6G IF-ED
Lens : 18-135mm f/3.5-5.6 G
Scale Factor To 35 mm Equivalent: 1.5
Field Of View : 7.3 deg (0.06 m)
Focal Length : 135.0 mm (35 mm equivalent: 202.0 mm)
Is there a possibility that the exif -> FOV calculation is not
accurate? (or is the camera misbehaving?) (the FOV in the exif could
be the vertical FOV, making the horizontal FOV 4/3*7.3 = 9.7 Hmm. it's
not using that!).
Roger.
(*) That is for Nikon DX sensors. The magic number is 2400 for full
frame. Hmm. That can't be right. There should be a factor of 1.5
between the two numbers.
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The plan was simple, like my brother-in-law Phil. But unlike
Phil, this plan just might work.
dkloi
edge, short edge) as approximately 12.2 degrees, 10.2 degrees, and 6.8
degrees for a 135mm lens on a 24mm x 16mm sensor. However, the actual
focal length of a lens can differ from the number printed on the lens
due to manufacturer round-off and changes with focus distance. Also,
APS-C sensors may be slightly smaller than 24mm x 16mm.
The angle of view can approximated (when d much smaller than f) by FoV
(degrees)=(d/f)* 180/pi, where d is the sensor dimension and f is the
focal length, both expressed in the same units. This gives the rule of
thumb FoV=1375/f for the long side of an APS-C sensor.
Cheers,
Daniel.
On Feb 19, 11:11 am, Rogier Wolff <rew-googlegro...@BitWizard.nl>
wrote:
rew
On Feb 19, 1:09 pm, dkloi <dkl...@googlemail.com> wrote:
This gives the rule of
> thumb FoV=1375/f for the long side of an APS-C sensor.
the
lens reports. Exactly the same as what Hugin calculates.
Could it be that the lens' effective focal length changes with
the focus distance? [.... time passes ....]
I checked. When focused "as close as possible" the lens'
FOV is about 25% larger than when focused at infinity. So
when focused close by the FOV may be as large as 13.6 degrees.
OK. Case closed. Hugin is right. The camera+lens fail to take the
reduction of the effective lens lens into account when they write
the exif info. At close range my 105mm lens may even be longer
than my 135 mm lens!
Roger.