Instrument specification
All twenty units are identical in optics, mount and camera. They differ only in the filters they carry, which is what allows the array to cover the full medium-band set in a few exposures.
Optical tube assembly
Each unit is a PlaneWave DeltaRho 500, a corrected Cassegrain of 508 mm aperture with a focal length of 1,537 mm and a focal ratio of f/3.0. The design delivers a 70 mm image circle covering approximately 2.6 degrees - fast optics over a field far wider than a conventional research telescope of the same aperture. Optomechanical alignment of all sixteen operational units is complete, and image quality is monitored continuously through routine survey operations rather than in scheduled campaigns.
| Model | PlaneWave DeltaRho 500 |
|---|---|
| Design | Corrected Cassegrain |
| Primary diameter | 50.8 cm |
| Focal length | 1537 mm |
| Focal ratio | f/3.0 |
| Image circle | 70 mm (≈ 2.6°) |
Mount
The DeltaRho 500 rides on a PlaneWave L-500 mount operated in equatorial configuration. Its direct-drive motors reach a slew rate of 20 degrees per second and sustain unguided tracking longer than the 100-second exposure used for survey work. Polar alignment is maintained through pointing models built by PWI4 from 40 to 50 sky points, and pointing and tracking accuracies are monitored continuously, with models refreshed when required.
| Model | PlaneWave L-500 |
|---|---|
| Drive | Direct drive, equatorial |
| Slew rate | 20 deg s⁻¹ |
| Unguided tracking | > 100 s |
| Pointing model | PWI4, 40–50 sky points |
Camera
Each unit carries a Moravian Instruments C3-61000 PRO. Its back-illuminated SONY IMX455 CMOS sensor measures 36 by 24 mm with 9,576 by 6,388 pixels of 3.76 micron pitch. At the DeltaRho focal plane this gives a field of view of 1.34 by 0.90 degrees at a pixel scale of 0.5 arcseconds - about 1.25 square degrees of spectral mapping per pointing. Bias levels are consistent with the manufacturer specification of roughly 3.5 electrons RMS, and the horizontal pattern characteristic of CMOS detectors is present but stable.
| Model | Moravian C3-61000 PRO |
|---|---|
| Sensor | SONY IMX455 back-illuminated CMOS |
| Sensor size | 36 × 24 mm |
| Dimension | 9576 × 6388 pixels |
| Pixel size | 3.76 µm |
| Pixel scale | 0.5 arcsec |
| Field of view | 1.34° × 0.90° |
| Operating temperature | −10 °C |
Filters
Every unit carries a nine-slot filter wheel. Three slots in each wheel hold Sloan g, r and i; one unit adds u and three units add z. The remaining slots hold medium-band filters, distributed across the array so that the full set is covered in a small number of exposures. The original twenty medium bands are spaced regularly at 25 nm from 400 to 875 nm with 25 nm FWHM. Fifteen more, procured from Edmund Optics and installed in late 2025, fill the gaps between them with central wavelengths from 412 to 832 nm and bandwidths of 14 to 41 nm. The current suite of 35 filters covers 375 to 875 nm, advancing toward the designed complement of 40 medium bands at 12.5 nm spacing.
The additional fifteen filters depart from the regularity of the original set: their central wavelengths are not precisely aligned to the 12.5 nm grid, their bandwidths vary, and no filter between 700 and 800 nm is included in the second batch. These departures reflect availability and will be addressed as the remaining five filters become available. Their spectrophotometric calibration is in preparation; the original twenty remain the calibrated set in operational use.
| Filter wheel | 9 slots per unit |
|---|---|
| Sloan g, r, i | Every unit |
| Sloan u | 1 unit |
| Sloan z | 3 units |
| Medium bands installed | 35 of 40 planned |
| Wavelength coverage | 375–875 nm |
| FWHM | 14–41 nm (typ. 25–30) |
| Manufacturers | Chroma (broad), Edmund Optics (medium) |
Filters are designated by central wavelength in nanometers — m400 is the band centered at 400 nm. System response curves, which fold in detector quantum efficiency, sky transmission and telescope optics, are shown under status and overview; photometric calibration and its accuracy are reported on the performance page.
What the filter set looks like
