SARG - Available Slits and their efficency
Available Slits
There are 9 positions available on the SARG slit wheel. They are used as listed in the following Table.
| Aperture | Resolution | Size
(mm) |
Size
(arcsec) |
Projected slit
(pixels) |
Notes |
| #1 | 29,000 | 0.30 X 1.50 | 1"60 X 8"0 | 9.8 X 49.1 | Short Slit |
| #2 | 57,000 | 0.15 X 1.00 | 0"80 X 5"3 | 4.9 X 32.5 | Short Slit |
| #3 | 86,000 | 0.10 X 1.00 | 0"53 X 5"3 | 3.3 X 32.5 | Short Slit |
| #4 | 164,000 | 0.50 X 1.00 | 0"27 X 5"3 | 1.6 X 32.5 | Short Slit |
| #5 | 43,000 | 0.20 X 5.00 | 1"07 X 26"7 | 6.6 X 162.5 | Long Slit |
| #6 | 115,000 | 0.075 X 5.00 | 0"40 X 26"7 | 2.2 X 162.5 | Long Slit |
| #7 | 144,000 | 0.30 X 0.30 | 1"60 X 1"60 | 2.0 X 68.6 | Image Slicer |
| #8 | Pinhole | 0.025 X 0.025 | 0"13 X 0"13 | Wavefront reference | |
| #9 | Mirror |
In the first column the position on board the slit wheel is indicated. Slits in positions #1, #2, and #7 are custom made slits. They are laser cut on 9.5 mm diameter polished stainless steel discs. Slits in positions #3-#6 are stock precision slits by Melles-Griot and Edmunds Scientific.
The slits are mounted with an inclination of 10 degrees with respect to the optical beam in order to feed the slit viewer.
Slits efficiency
Figure gives the transmission of slit aperture for different resolutions and in different seeing conditions. In typical seeing condition SARG efficiency at very high resolution is enhanced by using the image slicers. When computing efficiency given by the image slicers we considered 10% losses at each air-SF5 interface (coated with MgF2: this value should be approximately correct for an incidence angle of 54.6 degrees) and 2% losses at each face of the field lens, while we neglected losses within SF5 (given its small size, they are smaller than 2% even at the UV extreme of the SARG wavelength range, 370 nm). Note that projected slit width with this array is smaller than with the simple air slit.
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