Reason for using focal lengths between 25 ~ 50mm?

[kohyuk]

Is there a reason photogrammetry softwares recommend to use focal lengths between 25 ~ 50mm (full frame equiv.)?
Is it because values that are out of this range usually have heavier lens distortion?

The Laowa 12mm zero distortion(almost) lens looks amazing and captures images 122degrees fov.
But because of it's wide fov the perspective distortion is quite extreme!
Would this be a problem to 3DF Zephyr?

[Roberto]

Hi Kohyuk,

a focal range of 25-50mm is mostly suggested for two reasons. If you have a very low focal length you will get an highly distorted image, while if you have an high focal length you might have problems with Depth of field / blurriness (if you don't use tripod with low illumination) or low overlap as the viewed scene is less. However, all this problems can be easily solved if you pay attention during the acquisition or during processing. For example, a high radial distortion with spherical lenses can be easily corrected by Zephyr and you can use precalibration for extreme cases, but you might lose a little bit of resolution / sharpness in the process.

The lens you posted is an aspherical one and thus have a low distortion despite it's low focal length. It's fine for photogrammetry

[kohyuk]

Thanks for the reply!
Zephyr is an amazing program

[Scott Nebeker]

I've been trying to break Zephyr for what? A year now? Seriously, it's been a passion of mine.

I'll prove the point of how much a pain in the ass I am to the developers. Their main processes are "Samantha," "Stasia," and "Sasha." Each name beginning with 'S.' Well, my name starts with an 'S.' I pointed out this fact and they did something that makes me laugh far more than it should. Do this:

Open the Scripting Console (under Tools) and type "Scott" (without the quotes)

It's hilarious because it does exactly what I do, it introduced a new verb to the world and shows that these guys will listen.

My point is simply that those numbers are recommended not required