I'm trying to render visible beam of light on the theatre's stage.
Similar to this pict:
http://www.renderosity.com/mod/adman/photos/Ad16229.jpg

Please advice how to do it? Ready recipes are welcome, because results of try is visible after long rendering ;)

Should I work with spot light and atmosphere only?

spot light and atmosphere works well ,  a cone properly textured can be used to fake it

remember atmosphere requires something behind it to be visible , so you need a prop background

Quote - remember atmosphere requires something behind it to be visible , so you need a prop background

Did not know about it. I'll try.
Cone is not best solution, because I want to animate scene and move lights. In this case, area where cone cross ground looks terrible.

Quote - ..Should I work with spot light and atmosphere only?

I guess using a spot and atmosphere may give more accurate results.  Somewhere around here, there is a really good tutorial on doing lightbeams coming through windows and such.  IIRC, the promo-pic for that is something like a church, abbey or long/wide hall with mulitple widows on the right-hand side and light streaming through them.

For a quick and dirty way, you may be able to get a hi-res planar primitive and assign a transmap to it that is in the shape of your lightbeam.  Position that where you want it and then muck around with some materials settings in order to get it looking right.  Something as easy as a light texture with transparency bumped almost all the way up with a transmap (to give it a triangular/whatever shape) may suit your needs.

I think something like that would give a workable, and very easily directed solution.  I'm not big into the whole materials thing though so you'll have to fiddle with that.  What I know is due to trial and error with a lot of errors and trials... :)

In the image I did above, I used atmosphere for both the spot light and the IBL light. It would have looked weird if there was fog in the spot light and the rest of the scene was crystal clear.

I think I made it but cannot present results. Poser crashes in last stageof rendering :D
I love it.
Anyway I've seen 75% of picture. I used Daz freebies prop "opera stage", 6 infinite lights "no shadows" - up, down, left, right, front, back with 10% intensivity and 0 atmosphere str. Spot light has 0,1 atm str vs 0,01 default - looks exactly like light beam on the stage. I think I'll change infinity lights to point what let me keep everythink except scene in the dark.

Morkonan - I thought about transparent prop (I used it when rendered shower drops) but prop does not look good in area where it crossing another surface (in this cause stage's floor). I could not find any tutorial here but I hope I do not ned it now ;)

Thanks all. You really help. Now I'm turning off services in Windows to more memory. I'm happy that I'm using XP not Vista.

Old school, quick & easy from P4 days - using semi-transparent primitives parented to light.  Sphere in top pic, cylinder in middle pic & two cones in bottom pic.

That's a great technique Nance. Very effective and I'd guess it renders much more quickly than using atmospheres.

That is a cool idea, atmosphere takes forever to render most times.

I'm changing my mind and like semitransparent props much more then few days ago.

Atmosphere rendering is too advanced for my CPU. I've built my computer on my own and CPU is too close to power pack. Lack of ventilation overheat it and switch off computer :)
I took off covers but sometimes renders are still too "heavy". C'est la vie. I must fit my intention to my capabilities ;)
 

I hate to say this but I'm kinda new at Poser, so is there a tutorial or something explaining how to do semi-transparancy inother words how do you make something semi-transparent in Poser

 Hello xpac5896, and welcome to Poser

Take a look at one of the "stickys" called  "Material Room, Nodes & Shaders - Tutorials and Discussions" - you'll find tons of info there.  (look just above this  thread)

Also, be sure to check out Dr.Geep's website for tons more stuff.

take care

A lot more to it as you’ll see in the links by jdcooke above, but the short answer (in P6) is:

• with the object or figure selected, select the "Materials" tab at the top of the composition frame (or hit CTL-U). 

-  In the new Materials panel that opens, select the “Simple” tab at the top. 

-  One of the boxes in there is labeled “Transparency” and you can slide the Transparency dial there from 0% (no transparency) to 100% (completely transparent) for that single material.

• Applying a transparency map there will inhibit this effect in areas of the map shaded lighter.    (for the effects in my images above, no transparency maps were needed.)

a few more of them-thar pesky details on the effects in the images above:

-  "Cast Shadows" turned off for the "beam" props, 

-  and I'd have to check, (these are very-very old) but I believe the beam props' Diffuse color is set to 0 black (so they would not be affected by the scene's lights) and the Ambient color set to the actual color I wanted to see.