What is the best image brightness for photogrammetry?

Images made for photogrammetry, and indeed for anything else, should look nice. If you can see the features in the image, the software will see them as well. Balancing the previously mentioned settings as well as aperture is the key to properly exposed images. Aperture is the final factor that makes up the photographs' exposure.

For photogrammetric purposes it is usually best to keep the aperture wide open. Wide open means that the lens itself will let through all the light it gathers. Aperture is expressed as an f number. The smaller the f number - the more open the aperture is.

For example, aperture value of f2.8 is a good small number that lets a large amount of light to the sensor. F11 on the other hand is a more closed aperture that will result in less light. Some drones have fixed aperture lenses which means that you don’t have to worry about changing it whatsoever.