companion observations of a standard star. Details of each target are given in Table \[tab:obs\].

Instrumental setup and characteristics
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Throughout this work, a distinction is drawn between a *frame* (corresponding to one set of data read from the CCD), an *image* (a number of frames at the same etalon settings which have been combined for analysis) and a *field*, or stack of images of the same area of sky at different etalon settings.

### Wavelength variation and the optical axis {#sec:wlvariation}

Fabry-Pérot images have a quadratic radial wavelength dependence of the form $\lambda_\theta = \lambda_{centre}(1 - \theta^2/2)$ [@Bland89], where $\theta$ is the off-axis angle at the etalon. In a typical observation, the wavelength varies across the field by around 1% of $\lambda_{centre}$. Wavelength calibration is performed with respect to the axial wavelength; for any given pixel position on the image, it is then possible to calculate the wavelength observed at that point.

### Objects at $z \sim 2.2$

The TTF was used at $f/8$ on the AAT in combination with the EEV2 CCD. This resulted in a scale of 0.33” per pixel. After processing, the total useful rectangular field of view in the observations was around 7’ by 5’. 