A production run of a set of narrow-band and special filters was started in 1999. The specified center, cut-on, and cut-off filter wavelengths (µm) are given below.
|CO (2-0 bh)||2.316||2.292||2.340|
Note: "HK Notch" is a 1.47-2.4 µm filter with notch at 1.8 µm that blocks out the atmospheric water band. This filter is designed for deep imaging. The half-power points are at 1.48, 1.80, 1.98, and 2.30 µm.
The manufacturing specifications are the same as for the Mauna Kea near-infrared filters except for the items given below:
For the 1999 production run a long-wavelength blocker was also specified to suppress long-wavelength leaks. It was anticipated that achieving the out-of band blocking would prove to be very difficult, and this was the case. After delivery of the initial set of filters, some of the filters were found to have leaks near 4 µm.
The order-sorting filters and their wavelength ranges (in µm) are given below:
|Order sorter 1||4.40-6.00|
|Order sorter 2||2.90-4.25|
|Order sorter 3||1.92-2.54|
|Order sorter 4||1.47-1.80|
|Order sorter 5||1.17-1.37|
|Order sorter 6||1.03-1.17|
|Order sorter 7||0.91-1.00|
The thickness spec and tolerance are required to ensure that the focus does not change when changing the filters. These filters are not located at a pupil image, thus the optical thickness is required to be constant.
Note: The adopted optical thickness can be adjusted if it helps in manufacture or in meeting specs, provided all filters are not thicker than specified and all filters can be handled with reasonable precautions.