Filters are used to eliminate light from outside of the desired wavelength range. In particular, a blue-cut filter is used to eliminate second-order blue light when a red region is observed.
The filters installed in the system and their transparent wavelength ranges are
given in Table . The following shows examples of the filter
sets used in the standard setups for blue and red regions.
(ex.1) Red region (510-780nm): Filter 1=Free, Filter 2=SC-46
(ex.2) Blue region (340-510nm): Filter 1=SQ, Filter 2=Free
Since the optical path is changed by the insertion of filters, the focal length of the collimator is also changed. The standard position of the collimator is determined for one filter with a thickness of 5mm. This is the reason why the SQ filter is used for the blue setup (see the above example). The thickness of the ND filters is negligible. Therefore, the standard position of the collimator is applicable to the combination of one color filter and one ND filter. If the observation is done with a special filter or without any filter, re-focusing of the collimator system may be required.
Users should also take into account that the ADC cuts-off all wavelengths shorter than about 360 nm.
Filter | Turret | Coverage* | Wavelength region (setup) |
SQ | 1 | (quartz) | |
ND1 | 1 | (10%) | |
ND2** | 1 | (1%) | |
ND3** | 1 | (0.1%) | |
ND4** | 1 | (0.01%) | |
U340 | 1 | ?-?nm | ?-?nm (Blue?) |
OG530 | 1 | 590-980nm | 590-980nm (Red) |
KV408** | 1 | 434-774nm | 434-774nm (Red) |
He4686** | 1 | 467-470nm | 467-470nm*** |
O5007 | 1 | 499-503nm | 499-503nm*** |
O6300** | 1 | 629-632nm | 629-632nm*** |
Hα | 1 | 654-659nm | 654-659nm*** |
S6717** | 1 | 670-675nm | 670-675nm*** |
SC-46 | 2 | 485-896nm | 485-896nm (Red) |
GG495 | 2 | 550-900nm | 550-900nm (Red) |
SC-42 | 2 | 456-796nm | 456-796nm (Red) |
KV389 | 2 | 410-746nm | 385-746nm (Red) |
KV370 | 2 | 394-680nm | 394-680nm (Blue) |
WG335** | 2 | 393-606nm | 393-606nm (Blue) |
RG610** | 2 | 660-1120nm | 660-1120nm (Red) |
RG715** | 2 | 780-1200nm | 780-1200nm (Red) |
* For the short-wavelength-cut filters, the 99% transparent wavelength and twice the 1% transparent (i.e., cut-off) wavelength.
** These filters are prepared, but not installed, to the filter turrets in the standard setup.
*** These are narrow-band filters used in the longslit mode and without cross disperser.