Useful tips on writing TTF proposals

The signal-noise performance calculator is a good place to start, not least because it provides a summary of most of the free parameters which go into a proposal.

Detectors.  The CCD detectors available at the AAT  are detailed here.  The field of view and plate scales are shown below:
AAT f/8  (9' max field of view) AAT  f/15 (5' max field of view)
Tek 1Kx1K (24um pix) 0.594 "/pix 0.315 "/pix
MITLL2, MITLL3 2Kx4K (15um pix) 0.37 "/pix 0.20 "/pix
EEV2 2Kx4K (13.5um pix) 0.33 "/pix 0.18 "/pix

Resolution.  The key TTF  parameter is simply the resolving power you wish to use at a given wavelength. This figure illustrates the range of "safe" resolving powers across the optical window.

Choosing a bandpass. If you are unsure what bandpass to use, here are some useful tips.

Isolating orders.  The TTFs are periodic in their instrumental profile.  It is important to consider which blocking filter best suits your particular need. At small plates spacings, where the resolving powers are lowest,  the orders are well separated in wavelength (i.e. the free spectral range is large). It is possible to block light pollution from the neighbouring orders with conventional broadband filters. At the largest spacings, where the resolving powers are highest, neighbouring orders are closely spaced in wavelength. This requires much narrower filters to block the neighbouring orders. As a general rule, the blocking filter should be comparable to or smaller than the free spectral range.

This is what the distribution in FSR looks like:

   FSR  =   40 * lambda /  R

If you do not block the neighbouring orders, you are susceptible to (a) spurious emission lines appearing within your bands, (b) an increased sky background by a factor of the blocking filter width divided by the FSR. In this event, you will need to degrade the SNR result derived from the calculator by the square root of this factor (assuming, as in most cases, that you are background limited).

The TTF produces 40 independent spectral bandpasses between neighbouring orders, i.e., FSR  =   40  * lambda / R   =   40  * bandpass. Therefore, try to ensure that your blocking filter is at least comparable to this value, if not narrower.

The available broadband blockers are illustrated here. The available intermediate band blockers are shown here.  The RTTF blockers are shown superimposed on the atmospheric airglow lines here.  Note that the intermediate blockers give you 20% more coverage to the blue with filter tilts, as shown here.  Text files for all of the transmission profiles can be retrieved from here.

Atmospheric features. Surveyors of arbitrary emission lines at arbitrary redshift routinely forget to check what the atmosphere is doing in the chosen bands.  This is particularly true of  those important off band exposures. The TTF calculator incorporates a detailed model of the atmosphere based on echelle observations at the AAT and at CTIO.  Spend some time trolling through these plots. Note that if you are working in narrow bands, you could end up observing in an atmospheric trough with near zero transmission!

Shuffle modes.  The web tool for making arbitrary shuffle files is not quite ready. There are different modes of shuffling one might consider. For now, since the shuffle overhead is essentially negligible in all modes, proceed with your SNR calculations for each of the individual bandpasses required.