I have a problem when adjusting the level of a map. If the level > 0, it seemed OK, but when it is less than 0, it showed a solid box. This is different from EMAN2. In EMAN2, the threshold less than 0 also works. I'm not sure whether the defining of level is the same as the threshold in EMAN2. Or is there any other way to show the density of a map as in EMAN2 with threshold less than 0? 

Some snapshots of the visualization in both programs are attached to the post.

Thank you!