I saw something in another thread talking about render times so I wanted to know what exactly are the biggest culprits when it comes to long render times and what sort of things can be done about it.  For instance enabling ray tracing hair takes added render time.  However if you turn it off, you lose shadows for the hair if you are using raytraced shadows.  So in some instances you can get away with it, but not in all.

I mean there are times when something has taken an hour to render but I have no idea what to tweak.  When it comes to vendor products sometimes they have complex set ups and I have no idea what to change without having to worry about screwing it up or having to redo the whole thing.  I don't always even know if most of it is useless junk or if it serves a purpose.

BTW, I'm using P7 and 4 threads.

I am currently rendering a face framed by very detailed hair.  10 hours so far and not quite half way through..

P8 with IDL..

Transparency, reflection, refraction, low shading rate, all that increase render time

For tweaking you can disable shadows on far objects you can fake reflexion on tiny objects.

I don't know what image size you dealing with but a 1920x1600 wide screen only has 3.072 G pixels so if all those ultra highres texture maps are on bodies under shirts/coats vest cloak whatever  bend foliage or props. All those overlapping polys are one thing but loading all the pixel scaled maps is really  stress testing  a rig try this test render a scene with no maps then art program sample the image to get some idea how big in pixels that element of your scene is. Now proportion your textures (pixel sizes) resave HR textures to new adjacent folders and resize the saved file not the originals
Streamlining your map sizes saves a lot of resourses

A large number of ray trace bounces. Consider how many bounces to get the reflections you want, and consider a reflection map to fake it. 
Image size. Do you really need that pic at 6000 x 4000 pixels or would 3000 x 2000 do just as well.

I am not clear on the impact of large image maps on render times. Does a pic need a 3000 x 3000 texture for a character in the background thats maybe 100 x 100 pixels in the final render ?  The textures take up memory , and theres a limit on how much poser can allocate.

Displacement and bump maps can increase render time significantly.  Consider not using such mapping on distant objects or landscapes.  Medium distant objects, use bump maps, and anything close-up would need to be carefully evaluated.  If the scene contains full on normals, use bump; objects at perspective angles would require displacement. 

Quote - ...Does a pic need a 3000 x 3000 texture for a character in the background thats maybe 100 x 100 pixels in the final render ?.....

That's a 9,000,00 by 10,000 sample to image ratio
900/1!!!!!!
resolution overkill?  I think so

 Eyesplits - when the camera intersects geometry. A combination of the near clipping plane and the renderer's inability create micropolygons is a sure fire way to increase you render time (or crash the render)

Bad geometry - lamina faces, faces with zero area, etc.

Character density. An OBJ file is a list of points. Which file will read faster  - one with 8000 points or one with 80,000 points?

Always remember - choose bucket sizes and shading rates that prevent the renderer from sending information to the next bucket. For example, if your bucket size is 16 and your shading rate is 1, then your ideal grid size will be 256 (that is bucketSize^2 / shadingRate).

Considering that many people use 32 pixels per bucket and a shading rate of 0.2, each grid contains 5120 micropolys. 5120 is not a power of two number (and each bucket is square), which means that for each following bucket, 1022 micropolys are carried over from previous buckets, compounding. Could this adversely affect render times? Certainly.

Nowadays I believe it is unrealistic to exclude raytracing from scenes. People understand that it carries overhead and we / they just deal with it. But making sure your geometry and camera placement play to the renderer's strength, your renders can become speedier.

Raytracing:

• For simple reflections you only need one raytrace bounce. If you want reflections of reflected surfaces you need to increase that. For Refraction you might need 3 raytrace bounces if fresnel or refract is used.
• Start of with a quality of 0.1 for reflect/refract/fresnel in the material node. This is usually sufficient. Increase if needed.
• Set  blur in raytrace bounces to 2.0 or less. Increase only if softer shadows are needed.
• For indirect lighting you can set the IDL bounces independent of the raytrace bounces with a script in Scripts:Partners:Dimension3d:Firefly Render - Keep the IDL bounces as low as possible.

Rendersettings:
 - Set min shadow rate to 0.60 or higher initially. Decrease when needed.
 - For Poser 8 set bucketsize to 32, use external process and threads to number of cores on your system. For Poser 7 set bucketsize to 64

These will give the fastest rendertimes while keeping all the features. Tweak the individual settings for fine adjustments. With these in mind you can decrease rendertimes from hours into minutes

 Try a bucket size of 64 and a shading rate of 0.25 . I mean, 16384 micropolys is a lot but as a power of two number your buckets will process efficiently.

Thanks for the tips guys.

1. Anthanasius and hborre, yeah I kinda figured those things would be top culprits, but I wanted to make sure they weren't the only ones.

2. Jim and Mark, my typical render is anywhere from 800x800 to 1200x1200 and I can still see render times of over an hour on something that small.

3. Mark, I remember reading a post that said adding extra bounces in itself doesn't add to the render times.  It's when you start doing things that the bounces will take time.

4. replicand and wimvdb, thanks for the tip, that's something I am going to test out and the kind of info I was hoping to get.  I mean when I was playing around with bucket size and shading rate, I never figured make sure everything comes out as a perfect square.  Usually I'm using a bucket size of 32 and a shading rate of .25.

One thin gI've noticed that can drastically increase render time is Hair or fuzz.  Lots of fuzz or hair = lots of small shadows.  I shudder to think of the render time involved if one put the fuzzy version of the Bedtime sets plush bear into a mirrored room.

Quote - One thin gI've noticed that can drastically increase render time is Hair or fuzz.  Lots of fuzz or hair = lots of small shadows.  I shudder to think of the render time involved if one put the fuzzy version of the Bedtime sets plush bear into a mirrored room.

If You decide to try,  show us the result..  LOL  ;)