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Author Topic: Expected stability of camera parameters when using a DSLR + fixed focal lens ?  (Read 2977 times)

Bruno Andrieu

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My question is about using or not a fixed camera calibration.
I repeatedly use a same camera  (Nikon D5200) with a same single focal lens (50mm)
There is typically 0,5% variatiability in Photoscan estimated focal lenght between independent calibrations on similar scenes. I expect this to come from the calibrating process plus some flexibility in the camera+lens systems.
If for instance the true camera+lens characteristics would be stable within 0,1%, I should probably use camera fixed calibration.

I would like to know
- Is this 0,5% variability in the range of what is expected  (or low or high ?)
- Does someone knows what is the part of variability expected from  the camera+lens characteristics in my case (camera is attached to a monopod; variability over a period of several weeks, with usually mount/dismount of the lens, some change in air temperature, etc ) ?
Thx for any hint

Bruno

Marcel

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The focal length of a lens can also change based on the focus distance. So your 50mm lens might be a 51mm when focussed at infinity, and a 48mm when focussed at 1 meter distance (numbers purely hypothetical).

If your focussing point changes in distance a few meters than this could be the cause of focal range variation.

Bruno Andrieu

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Marcel

Thx for this hint.
In my case the focus distance is always between 1m and 2 m, so (hopefully)  there should not be to much of this.

Since  Agisoft propose the lens software, I would expect that they are significant cases where a fixed calibration would be the best choice but I am usure if I am in this case.