Well, I realize there's no built in option to make a HDRI render. But just as well as you could merge a set of photos into a HDRI in Photoshop, I'm thinking I could just as well merge a set of renders into a HDRI in Photoshop.

The basics of HDRI is having a set of photos, exactly the same scene, but with different exposures. I can set the shutter speed and the aperture size in my camera to do that. But is there any way to adjust the overall exposure in Carrara?

Mark Bremmer has a tutorial on his Dark Arts page

Thank you, but that is a tutorial on how to make a HDRI map for the scene. This is for setting up HDRI lights. But I'm talking about making a HDRI render. Well not render directly to HDRI, but to render a set of images to merge into a HDRI result.

When I saw your reply in my mailbox I realised my mistake. I have read about what you want, do not remember where. One of the solutions was to render an animation, where the opacity of a black sheet in front of the camera was animated. But I think that is technically not the right way to create an hdri.

I think changing the light would mimic reality the best.
Using the master light might be good trick. The animation trick is still usefull. You could start your scene with the lights (and ambient light) all turned high, and end with it to almost none in 6 frames. Render the frames as sequenced photoshop docs and merge them.

But I have not tried it myself :)

Ah, yes! The animation thing sounds interesting. Like you said, is probably not technically right but it might reveal some interesting results. I'll try it, thank you for the tip!