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On Sun, 19 Mar 2006, George McNamara wrote:

> I inputted to the PFIG Resolution Calculator Applet at
> http://www.pfid.org/html/objcalc/?en [...]

Results:

> Resolution at sample (button) assuming pinhole size of 1 Airy unit
> Theoretical XY resolution = 220 nm
> Theoretical Z resolution = 615 nm
[...]
> Nyquist XY sampling rate = 110 nm
> Nyquist Z sampling rate = 308 nm

It seems that this calculation of the Nyquist rate is based simply in
dividing by two the spatial (Rayleigh) resolution, which is not exactly
right. The definition of the Nyquist rate is based on the system bandwidth
(in the frequency space, not using real distances). Despite the "divide
the resolution by two" rule of thumb usually gives a good first estimator,
this may lead to some undersampling in many circumstances. (See e.g.
http://support.svi.nl/wiki/NyquistRate).

For a confocal with NA = 1.2 objective in water the Nyquist rate is about
one sample per 60 nm in lateral directions, and one per 180 nm in axial
direction.

Cheers,

jose.