24
The pictures on the left demonstrate the influence
of pixel time and averaging on SNR; object details
can be made out much better if the pixel time
increases or averaging is employed.
Another sizeable factor influencing the SNR of an
image is the efficiency of the detection beam path.
This can be directly influenced by the user through
the selection of appropriate filters and dichroic
beamsplitters. The SNR of a FITC fluorescence
image, for example, can be improved by a factor
of about 4 (6 dB) if the element separating the
excitation and emission beam paths is not a neu-
tral 80/20 beamsplitter
1
but a dichroic beamsplit-
ter optimized for the particular fluorescence.
Fig. 20 Three confocal images of the same fluorescence
specimen (mouse kidney section, glomeruli labeled with
Alexa488 in green and actin labelled with Alexa 564
phalloidin in red).
All images were recorded with the same parameters,
except pixel time and average. The respective pixel times
were 0.8 µs in a), 6.4 µs (no averaging) in b),
and 6.4 µs plus 4 times line-wise averaging in c).
a)
b)
c)
1
An 80/20 beamsplitter reflects 20% of the laser light
onto the specimen and transmits 80% of the emitted
fluorescence to the detector.
337_Zeiss_Grundlagen_e 25.09.2003 16:16 Uhr Seite 27
