Fig. 3.

Spectral analysis of filter combinations of the 480-nm excitation filter and three potential emission filters. At 520 nm within the emission band of green fluorophores (green fluorescent protein [GFP], Alexa-488, fluorescein), all three combinations performed equally well. However, at shorter wavelengths, they differed significantly, resulting in different background transmission capabilities. The 515-nm long-pass interference filter almost completely blocked background transmission, whereas the two glass filters (GG495 and OG515) achieved a more desirable signal-to-background ratio. The background ratio of GG495 was appropriate for generating a non zero background for navigation and signal detection without fully saturating the charge-coupled device (CCD) which can cause loss of detail