Emulating HDR using 3 geospheres

I rendered out an equirectangular image (look it up using Auntie Google, if unfamiliar) using Daz Studio Pro. To get a bracket HDR, I adjusted the image in Clip Studio Paint EX to create one underexposed image and one over-exposed image. I therefore end up with three equirectangular images - the original, the underexposed one, and the over-exposed one.

I go into Poser Pro 11.x and load 3 geospheres. The geosphere prop is part of the Poser default content and its geometry works with equirectangular images for 360 backgrounds. The geospheres have to be enlarge to form an immersive skydome for your scene (example, size=17500). Then make one geosphere just one unit smaller (example, size=17499), and the next one two units smaller (example, size=17498).

After that, I go into the Poser Material Room, I created a Cycles root surface emission shader tree for each geosphere. The Cycles shader tree of the middle geosphere gets the image I rendered in Daz Studio Pro. The outermost geosphere gets the overexposed image and the inner geosphere gets the underexposed image. I adjust the emission and transparency node values of the inner geospheres until the scene renders acceptably in Superfly.

Basically, I have faked a bracketed HDRI. Here I show the L'Homme figure in my emulated HDRI environment. All the illumination in the scene is coming from the three concentric geospheres. I used the Poser default content Square Plane with Vince Bagna's Superfly wood shader. I modelled the dynamic clothing set in Shade3D. I created the textures for the clothes using Clip Studio Paint EX. The cap is from EF-Steve assets but I reversed its position on the head.

So why not just use an HDRI on one Geosphere ? Well have you seen the size of HDRI files ? if you have an old computer like mine, no way to load the file and get the rest of the scene working.