With this increase in photons (and rendering time), we find that our missing tendrils of light are more visible now. We could take the value up even higher, but this should be something for you to experiment with at another time. For now, see below my two renderings done with the caustic photons set to 150,000 and 500,000 respectively:


As seen, increasing caustic photons improves the definition of the light we see reflected/refracted from our objects.

Step 11: HDRI in mental ray - Finally, what this tutorial is all about, HDRI. The beauty of HDRI is that it brings to 3D art an element of reality that was sorely missing beforehand, but we never realized it until we had it. With Splutterfish it's almost criminally easy to use HDRI, so, here we go. HDRI isn't applied to any object like a material or as a map to any light, instead it's applied to the environment. Still in the camera position, hit 8 to call up the Environment and Effects panel. Under Common Parameters in the Background area, click the None button for Environment Map, in the Material/Map Browser double click Bitmap to bring up the Select Bitmap Image File window. If necessary, maneuver to the directory HDRI where you placed your *.hdr file (you may need to access the drop down menu for Files of type, selecting either All Files or Radiance Image File). Once found, double click the file to call up the HDRI Load Settings panel. It's on this panel that you make any adjustments to the *.hdr image before applying it to the environment. The adjustments of HDRI files are beyond the scope of this tutorial, but as a rule of thumb, the white point and black points are usually adjusted to values where both white and black clamping (indicated by magenta and cyan respectively) just disappear from the thumbnail. It's also a matter of artistic taste and what your needs are for the particular project you're working on. For now, stay with all default values, but DO make a note of the White Level Linear
value, see below:




Click OK, and the map is assigned. Now, it's necessary to copy this map to the Material Editor for us to use it in our scene. Hit M to call the Material Editor up and make sure the Environment and Effects panel is clearly visible. At this time, click and hold the left mouse button down on the Environment Map button and slide this over to the next available material slot (should be number 6) and release the mouse button. Choose Instance and click OK. See image below