Hi Tom,
You need to switch on the Post Effect to get a clean result with the Object Buffer in R17. The Compositing Tag sits “on” the hair object. Hair Mulitpass Alpha is on. I notice that the AA off is better. The Hair Alpha will be created, but perhaps ignore it.
The Hair>Multipass option is not available in Physical Render.
If you encounter problems that indicate a code based problem, please check this with the support.
https://www.maxon.net/en-us/support/how-can-we-help/
The Render Settings >Hair> Multi-Pass> Alpha> Separate is a different story. I do not get with R17 the result that I get as with R18.
I assume that you like to stay in “Hair Mode”, instead of being in Attribute Manager>Generate>[Generate] Type>”…” which would enable other options, e.g., Circle allows for great results,but do some tests, and adjust perhaps the Attribute Manager> Hairs> Guides.
You can see the effect in this clip here, one minute:
https://www.amazon.com/clouddrive/share/Ngv3UbfiT2VMeY96cyZK8SMtFPOHKC3yA1XzBhHIihi?ref_=cd_ph_share_link_copy
The Raster option as in R12, 13, etc., is gone.
https://www.cineversity.com/forums/viewthread/471/
All the best