Aperture Plates and Filters
The aperture wheel, the shutter, and the upper and lower filter wheels are used for both Blue and Red Channel.
The aperture plates are tilted 12.5° with respect to the optical axis to allow for reflection to a slit viewing acquisition and guide camera. The available aperture plates are listed in the table below. The aperture wheel will accept up to seven aperture plates at a time. One position in the wheel has been modified to allow the aperture to be changed while the spectrograph is mounted on the telescope. Observers may request any aperture plate for this position. The other six positions are typically populated with the 180″ long slits excepting only the 0.75″ wide slit.
The 20″ and 9″ slits are generally used for the Blue and Red Channel echellettes, respectively, in cross dispersed mode. The last two columns provide the FWHM of a Gaussian fit to an unresolved comparison lamp emission line as a function of the width of the entrance slit. In both cases a low-resolution grating was used, so the anamorphic factor is near unity. The CCDs were not binned on readout. Selecting the links in the table entries will display measured profiles.
Note that the comparison lines are not well approximated by a Gaussian for wider slits so the quoted FWHM are not particularly accurate.
Standard Slits: (√ = available)
| Slit Width (arcsec) | 180″ Length | 20″ Length | 9″ Length | Blue FWHM (pixels) | Red FWHM (pixels) |
| 0.75 | √ | √ | 2.6 | ||
| 1.00 | √ | √ | √ | 2.8 | 3.2 |
| 1.25 | √ | √ | √ | 3.1 | 3.8 |
| 1.50 | √ | √ | √ | 3.6 | 4.1 |
| 2.00 | √ | √ | √ | 4.5 | 5.3 |
| 3.50 | √ | √ | √ | 7.9 | 10.0 |
| 3.75 | √ | ||||
| 5.00 | √ | √ | √ | 11.5 | 16.0 |
Special Purpose Slits:
Comb – line of 1″ diameter circular holes on 10″ centers
3″ diameter single circular hole
1.0″, 1.4″, and 5.0″ diameter double circular holes
1.0″ x 2.6″ and 2.0″ x 3.0″ double slits
1.25″ x 90″ slit for use with the Blue Channel cross dispersing prism
90″ circular hole for direct imaging
Slit Length: The finite size of the filter wheels vignettes light near the ends of the long slits. The unvignetted slit is about 150 arcsec long. The following links show plots of the intensity along the slit. For this data, the CCD was binned by a factor of two in the spatial direction, giving a spatial image scale of 0.6″/pixel, twice that of the nominal unbinned scale of 0.3″/pixel.
A Uniblitz shutter is located below the slit assembly and above the filter wheels. The shutter is controlled by the data acquistion computer and the CCD controller.
Each filter wheel has seven filter positions and one clear position. Each position can accommodate a 2-inch square filter with a thickness of up to ~6 mm. The available filters and their transmission curves are provided below. Filters cannot be changed while the spectrograph is mounted the telescope so please contact MMTO staff if you require a non-standard filter configuration. The two filter wheels are currently populated as follows:
Upper Wheel:
- Clear
- 2.5 Mag
- R-63
- L-38
- ND 0.5
- 1.25 Mag
- UV-36
- L-42
Lower Wheel:
- Dark
- CM500
- CuSO4
- LP-530
- U-330
- LP-495
- 14th Order
- Clear
The filter transmission curves provided below were measured in 1989 by Sally Oey using the monochromator at NOAO.
Blue Blocking Filters: The following filters are available to block light from higher orders. A plot of the filter transmission curves is available in pdf or png format.
- UV36
- L-38
- L-42
- LP-495 (Y-50)
- LP-530
- R-63
Red Blocking Filters: The following filters are available to block light from lower orders. A plot of the filter transmission curves for the CuSO4 and U330 filters is available in pdf and png format and for the C-500 and CM-500 filters is available in jpg format and gif format. Or see the Hoya Color Compensating Filters Page.
- CuSO4
- U330
- C-500
- CM-500
Larger Filters: We also have a few larger 6-in x 6-in filters. A plot of the filter transmission curves for the larger filters is available in pdf and png format. Blue Channel Echellette Order Sorting Filters: PDF plots of the echellette order-sorting filters are available below. Note that these are not usually resident in the spectrograph, so prospective users should contact the Instrument Specialist well in advance of their run.
Hoya Filters: The following standard Hoya Glass 2-inch square filters are kept on hand at the MMT. Consult a Hoya catalog for transmission curves. Note that these are not usually resident in the spectrograph, so prospective users should contact the Instrument Specialist well in advance of their run.
- ND 0.3
- ND 0.5
- ND 1.3
- ND 2.5
- ND 4.0
- ND 5.0
- ND 7.0
- U 360
- UV 28
- O 54
- O 56
- B 390
- R 60
- R 68
- IR 85
- LB 120
- LB 145
- LB 165
- LB 200
- LA 120
- RM 90
- Y 48
- V 10
- G 533