I was trying to work out if there's an upper limit to the overall total number of  hairs that Poser can actually deal with but I've had varying results as to when a render has failed. It may be that it's dependant on what else is going on in the scene.

I also need to amend something I said earlier about turning off the 'Opaque in Shadow' setting on the hair node - you can't always do this, and not for all groups. I still can't quite get my head around what the hair node is doing. Specular is a bit of a struggle for sure.

 

PoserPro2014(Sr4), Win7 x64, display units set to inches.

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