The Signal calculation involves variables that directly relate to the foreoptic and slit:
$$
s_{\text{optic}} = \frac{1}{f_n^2}\cdot
\eta_{\text{optic}}\cdot
\epsilon
$$
Where
- $s_{\text{optical}}$ [%]: The factor of the signal calculation (used for the Signal-to-Noise calculation) that relates to properties of the foreoptic and slit.
- $f_n$: F-number of the foreoptic.
- $\eta_{\text{optic}}$ [%]: Transmittance of the optical system.
- $\epsilon$ [%]: Fraction of light blocked by the slit (slit area divided by image diameter from the foreoptic incident on the slit face).