Lee Skinner wrote:

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What's weird about this one is that the bottom part of the planet's "rings" disappears when drawn at the higher resolution of 1600x1200, instead of being drawn sharper!

Jim Muth replied:

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You are probably using passes=g. What's happening is that the first coarse pass is probably missing the thin line and assuming that nothing is there on the subsequent passes. Try rendering the image with passes=t, or if that fails, passes=1.

The lower "rings" come into view only with 640x480 and 1280x1024 if passes=1. At 800x600, 1024x768 and 1600x1200 they disappear. But at 1280x1024, they go all the way to the bottom of the screen - but, like you say, changing to passes=g will also cause them disappear. Apparently the line is so narrow, that some of the resolutions miss it entirely, even at passes=1.