Motorised pinholes are fitted in the Hyperion microscope, controlled with a QEGui program. While the pinhole sizes are fixed, the projected aperture (i.e. size of beam hitting sample and detector) will be dependent on the technique and the objective being used.
The calculation is simple enough:
For transmission:
Spot size (μm) = pinhole size (μm) / magnification
For ATR experiments, the refractive index (n) of the crystal being used needs to be factor in:
Spot size (μm) = pinhole size (μm) / magnification / n
The final considerations when selecting pinhole size are resolution and signal intensity. Please refer to the appropriate sections on diffraction limited resolution and spatial resolution for a discussion of these topics. A “typical” signal count for each experimental technique can be found below (NOTE: values are an indication only and may vary over time).
Below is what the QEGui looks like. Note the selected objective. The selected objective is the “standard” for the technique, but we do have other configurations. Please contact a Beamline Scientist to discuss your project further.
