I used a camera focus point at 6.5 meters from the camera. The aperture diameter is 50mm. This emulates the performance of a 33mm focal length lens with f stop set to 0.6.
There
are real lenses that have come close to that --- they are rare but some have been made. That would be one expensive piece of glass, but it's cool that Terragen can use whatever mild or wild lens parameters you give it.
Here is a Zeiss 50mm with maximum 0.7 f stop made for the Apollo missions. Be prepared to pay $80,000 to $100,000. But they can be rented.

And here is the exact lens specs I used in reality. Something made by Signal Corps Engineering :