better filters to distinguish GFP from autofluorescence?

I was wondering if anyone might have advice on filter selection to improve 
the discrimination of weak GFP expression and autofluorescence.  We're using 
an EPICS XL with a 488 laser on mammalian cell lines expressing emerald GFP 
(peak excitation 487 nm, peak emission 509 nm).

The filters we're currently using for this are a 550 dichroic longpass a 
525/15 bandpass.  Is there room here for improvement?

Thanks,
Chris

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Christopher Logg
University of California, Los Angeles