Mighty peculiar. The trick to doing tests like these is to change as few variables at a time as possible, and note the differences. What seems to be happening here is that the falloff is interacting with the **scale** of the camera -- which Poser changes on its own (along with the camera position) when you change the focal length. It must be how they simulate the focal length effect, since the camera doesn't really have a "lens" to adjust. Nance's example file had the camera's focal length at 110 and the scale at 300. Once I set them back to 35 and 100 (the default, and the settings I used in my tests previously), the falloff worked as expected, as shown in the top screenshot. I've added some measuring sticks (stretched square props) to help indicate the distance: 0 is at the light location (z=2.7), the others at whole unit positions as shown. The front of the steps prop is at z=1 (1.7 units from the light), while the "wall" is at z=0 (2.7 units from the light). I've also pasted in a shot of the light settings, which are the same in all screenshots. With Distance Start = Distance End = 2, the light reaches the top couple of stairs, but not the measuring stick at 2. Then I changed the focal length to 70. Poser altered the camera position and scale as shown in the second screenshot, and you can see that the falloff pattern has also been altered. According to the manual, the camera "scale adjusts the dimensions of the studio in the window." That is, it seems to act as a **multiplier** for the dimensions. That's why the falloff is changing: at 200% scale, the falloff settings are effectively 200% of what the dial shows, or in this case, 4 -- as shown in the third screenshot, with the steps moved back by 2 units. As in the second screenshot, the light reaches the top part of the stairs (at 3.7) and cuts off before reaching the measuring stick at 4. In the fourth shot, with the steps back in the original position, I reset the scale to 100, and the falloff was back to the same as in the first screenshot: the light reaches the top couple of stairs, but not the measuring stick at 2. So to get predictable results, be careful to ensure that the scale of the camera is at 100%. If you want to do a "vertigo effect" (which I believe is the name given to Hitchcock's effect, since he first used it in the movie "Vertigo"), as JKeller said, you'll have to animate the distance falloff -- if the falloff is important in the scene, otherwise just set them to 0 to shut off the effect. At least now there's a way to calculate what they should be. So, set the first frame with the camera at 100% scale; set the last frame at the desired focal length, note what the scale is, and multiply the distance falloff start and end by that percentage to get the numbers for those settings in the last frame. Another funky thing I've noticed, if you change one of the default infinite lights to a spotlight, both distance falloff dials are created with maximum limits of 1, so if you have "Use Limits" checked in the Figure menu, it won't let you set them above 1. Just double-click the dial and enter a high maximum value, if you don't want to shut off limits (which may affect your poses). If you create a new spotlight, the maximum limit is set for a very high value already. By the way, I didn't know this stuff before -- I've learned it over the past couple of days in working out this puzzle and figuring out why we're seeing these effects.