[click on image to see a larger one]
It is a shorter wave filter (center is 340nm) and its transmission is this, as compared to the Baader (Venus) U filter (red line):
Here now some first impression about using the Jupiter-U filter. Target was a Gazania flower. Left: Venus U2, right Jupiter-U: 
Here VIS comparison shots: Baader-U (Venus U): 
Jupiter-U: 
Interesting to note the metallic golden rendering of leafs: 
Here now using a bred Kalanchoe floower in a quadriptych showing the VIS image (top left), Baader U2 (top right), Jupiter-U (bottom left), special 300-350nm filter (bottom right) 
and in more detail: 
If you look closer at the flower center, you'll notice only in the two shorter wave shots on the bottom a variation of reflectance (indicated by changing colors) [To make things clear, this is a filter for my work, it is not for sale.]
Stay tuned, more will follow on that fascinating subject...
More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos
