What exactly is the effect you are trying to create? It's not *just* a large sun, right? Because that's fairly easy in Terragen 4 as well.
Use "Visible Disc" in the Sunlight node settings and increase Angular Diameter until you get the size you want. If you are rendering with water/reflection, increase "Minimum highlight spread" until the reflection size of the sun matches the visible size in the sky. Files attached for example.
If that's not what you want, then some details/example would be helpful (it could be an image from TG Classic, for instance).
If it is that you don't want the sun disc to be so sharp-edged, then admittedly that might be an issue. But this is generally how it is in real-life too. The sun is pretty uniform across its visible surface most of the time, at least to the naked eye (if you dare look that long
). Sometimes it will have a gradient of color near sunset as it descends into haze and light gets scattered disproportionally at the top vs. bottom. But as far as I can think of it shouldn't be noticeably brighter in the center vs. edges. I've attached an image and TGD also demonstrating sunset across the visible disc (which is a cool effect).
Note that all of this is a faked, i.e. not realistic, approach. I know realism is not necessarily everyone's first priority. But if you want to replicate how photographers achieve the large sun look, you would keep Visible Disc the same size and instead zoom in with the camera, i.e. use a narrower FoV, a longer focal length.
- Oshyan