Last time we discussed this, bloodsong pointed our attention to the theory that Distance Falloff was effected by the focal length of the camera used to record the scene via the scale of the camera. Atleast, that's how I understood it. Nance brought up the 'Vertigo effect' as a special case where this may cause a problem. A combination of boredom and curiousness drove me to recreate the legendary shot first devised by Sir Alfred Hitchcock (and any technicians that may have been attached to the discovery).

A 190kb QuickTime 4 movie file can be viewed here here.

Details:

As you will see in the above image, after animating the focal length of the Dolly Camera from 35mm to 22mm and moving the camera forwards (down on the Y axis in this case) by a distance of 1.000, it turns out that no adjustment of the distance fall off of Light 1 was necessary. I'm planning on making some adjustments to this test to allow for a greater change in focal length, but it seems to me that focal length has no effect on falloff or any parameters of a spotlight. So, I quote myself when I ask...

"What am I doing wrong?"

Oh Noooo! This requires far too many brain cells for a Sunday morning -- before coffee. :-0

Attached Link: http://drsga.virtualave.net/mov/vertigo.mov

uhhh... i know nothing about lights and cameras. i was just an innocent bystander!! :)

Ok, I was able to figure this out. My experimenting is telling me that focal length really has nothing to do with distance falloff, but it is the scale of the camera that is the true issue. As petercat pointed out in the last thread, when you adjust the focal length, Poser automatically alters the scale and distance of your camera. Well, this is true for the Main, Aux and Posing cameras (and probably several of the others), but this doesn't happen on the Dolly Camera. On the Dolly Camera, you can adjust the focal length without effecting any of the other dials. Also, on the Main Camera (as well as the others that work like it...Aux and Posing) you can change the scale independantly of the focal length.

Lets say you're using your main camera. Focal at 35mm, Dolly Z at 10.000 (keep X and Y at 0 to keep it simple) and Scale at 100%. Now change your Focal to 70mm and Poser automatically adjusts Dolly Z to 5.000 and Scale to 200%. If you were to render now, your falloff settings would not give you the desired results. But, now we can change the Dolly Z back to 10.000 and the Scale back to 100% and the Focal length will stay at 70mm. Now render, and you will see your desired falloff results.

Of course if you use the Dolly camera, adjusting your focal length never messes with your scale and you don't have to worry about this at all. So my question now is, why does it have to mess with your scale and distance on the Main, Aux and Posing Cameras?

(P.S. bloodsong, I've seen your work. I think you know more about lights and cameras than you think you know.)

(shhhhhhhh!!!) you want my opinion, i think its the way they built poser. i think that changing a camera focal length is too hard to program, so they just changed the scale of the camera and got the same effect, so they left it. now, they couldn't do that with the dolly camera because... as i understand it... the dolly camera stays on a track around the center of the universe, and they couldn't move it around or... something. anyway, email curious labs and tell 'em to make this more logical, huh? :)

Had that cup o'coffee yesterday - went to work - & just got back 30 hrs later. Just wanted you to know that we're following your journey here (though haven't seen your flik yet). Sounds like you've eliminated another variable from the mix.

Actually bloodsong, the way you described the Dolly camera is more like the Main or Aux cameras. The Dolly camera is the only camera in the Poser line-up that rotates around its own axis. With the Dolly camera you can pan, pitch and yaw...which ultimately gives you more realistic/predictable camera moves than the orbiting that the Main and Aux cams allow.

The focal length CAN be changed on the Dolly camera and with predictable results without altering its position or scale. This is proof that they were able to program focal correctly (or that they were able to hide whatever trick they used from us and the physics of the rest of the scene).

I always use the Dolly camera anyway, because it moves like I want it to move for my animations. But I think that, due to what we've found here, the Dolly camera should be the camera of choice for any render, animation or still, where lighting is important.

E-mail curious labs? You must be kidding. They might actually have real answers for me and that would take all the fun out of figuring this stuff out. That's almost as bad as reading the manual!

BTW, between the last thread and this one, I got the Pro Pack. When I save a .pz3 where I have the distance falloff set, the next time I load the .pz3, the maximum limit on both the distance min and distance max are set to 1.000 as well as the values themselves. I don't even have Use limits turned on and I can't set it past 1.000 until I've raised the maximum limit. Has anyone else noticed this?

oh. SEE! i TOLD you i dunno nothing about cameras and lighting! :) now, i might know about composition and shadows... but that's different. i only use the top, left, right, main, face and hand cams. :: btw, while you're messing around... can you figure out what 'hither' is on the cameras? somebody on the tech forum here wants to know. :)

When I last checked the ptech forum, petercat had already answered that question. Hither is an area infront of the camera where poser will make items invisible so as not to obscure the shot.