# Dual mirror telescope optics

The size, shape and position of the primary mirror tiles are given via
the parameter, either as the parameters of the segments of the ring or
as a list explicitly defining the parameters of each mirror in the case
of hexagonal or circular mirrors. The mirror tiles are positioned on the
primary and secondary dish following shapes defined by polynomials with
parameters set by and respectively.

## Optical PSF

The optical PSF of the telescope is affected by

1.  the type of optics and size of mirror tiles;

2.  the micro-roughness of the mirror surface;

3.  the shape deviation of the single mirror tiles from the polynomials
    defining the dual optics;

4.  random misalignments and misplacements of the mirror tile on the
    dish.

Items 2 and 3 are intrinsic to each mirror tile and their effect can be
quantified in the laboratory by measuring the spread of directed-light
on the single mirror tiles (item 2), and by determining the difference
between the expected and measured direction of reflected light (item 3).
More details on these measurements can be found in
Ref. [@measurements-document]. In the simulations, the small-scale
roughness of the mirror surface is taken into account with a Gaussian
smearing of the reflected photon direction according to an r.m.s. spread
given by the parameter (for a better description of the tails of the
PSF, optionally the sum of two Gaussians can be used). At the moment,
the effect of items 3 and 4 is not taken into account in the simulation
in the case of dual mirrors. An effective way to take into account the
effect of item 4 is to increase the parameter in order to match
measurements made with the telescope.