When used with the Loral 1K x 3K, the echelle grating will have a 3 pixel resolution of approximately 3.6 Angstroms/order#, e.g. .36A at 5600A in 10th order. In all orders, the resolution will be approximately 56120/3.6=15,000 and the coverage will be 1024 times the resolution.
There are two filters for each order, centered at n.25 and n.75 where n=the order number. Each filter is made as wide as possible without permitting significant amounts (maximum .5%, average much less) of any undesired order to pass through.
If the filters were perfect, this would mean that a filter centered at order n.25 would cover from (n-1).75 to n.75 and the filter centered at n.75 would cover from n.25 to (n+1).25. There is therefore always a filter that covers from the overlap zone below the blaze to well beyond the blaze of every order and another which covers from well below the blaze to beyond the overlap zone of every order.
Since the free spectral range is larger than the size of the chip, this means that there is always an optimum filter for every wavelength range.
The filters become less efficient and the skirts wider as the wavelength becomes shorter.
See the appropriate section of the Argus User Manual for further information.
Exact transmission curves for these filters are given in the CTIO Filter List
Filter Order Center Width Transmission
(Average)
#1 5.75 9695A 1492A 75%
#2 6.25 8920A 1249A 84% *
#3 6.75 8259A 1058A 84%
#4 7.25 7689A 907A 87%
#5 7.75 7193A 784A
#6 8.25 6757A 684A 79% *
#7 8.75 6371A 601A 78% *
#8 9.25 6027A 531A 75% *
#9 9.75 5718A 472A
#10 10.25 5439A 422A
#11 10.75 5186A 379A 75% *
#12 11.25 4955A 341A 75% *
#13 11.75 4745A 309A 75% *
#14 12.25 4551A 280A 70%
#15 12.75 4372A 255A 65%
#16 13.25 4207A 233A 47%
#17 13.75 4054A 214A 44%
#18 14.25 3912A 196A 35% *
#19 14.75 3780A 181A 40%
#20 15.25 3656A 167A 50%
Notes:
1. Central transmission of the filters were measured in parallel light. Central transmissions of bluer filters may be 5-10% less in Argus because they are being used in an f/2.5 beam.
2. Filter #18 does not have a flat top, but has a single central peak at the design wavelength. The average transmission over the pass band is about 35%, rising to almost 50% at the peak.