Standard Quat Mandy by MakinMagic

Created using Ultra Fractal.

On further investigation I discovered that the algorithm I was trying for distance estimation was just the standard method in disguise - and the standard method works better
However I was tryng to find a better method because I wanted a method that allows you to render 3D/4D fractals such that the distance from the "inside" is fairly large and when using distance estimation this leads to visible "stepping" on the images.
In my iteration density method this issue was fixed by performing a binary search when solid is found to get the exact boundary and I'd previously tried implimenting this method for when using DE and failed to get it to work properly, however, convinced it *should* work I tried again and fixed the mistake I was making and here's the first result - as you can see the distance from the "inside" is quite large but we have a pretty much perfectly smooth render, at a cost of around 5% to 10% slowdown when rendering like this one, less overhead when rendering closer to the "inside".
This took 1min 19secs to render to disk at 2048*1536 on my heat impaired 3Ghz P4HT in single threaded mode (about 4 seconds to render at 640*480 in a UF window - also single threaded).