Wide field three colours simultaneous imager (as of 2014/7/14)

Basic info.

Type of telescopePure Ritchey-Chretien system
Diameter of the primary relection mirror510mm
F-ratio of the primary relection mirror3
Coating the primary relection mirrorAl with the SiO protection layer
Total focal length4080mm
Usable backfocus from backflange360mm
Field of view24 x 24 arcmin2
Pixel size13.5um
Available bandsSDSS-u, Rc, Ic
Optical elementsFused silica
Focal length with corrector4250mm
Pixel scale0.68mm
Tracking accuracy0.3arcsec rms w/ open loop (expected)
Pointing accuracy< 3arcmin
Maximum slweing speed2 degrees/sec

Optical layout

We adopt Ritchey-Chretien system to eliminate spheriacal and coma abberations. Introducing two spherical same material corrector lens system, we can obtain fine image quality up to 0.5 degree of field of view (Wynne 1968). We divide the telescope beam into three channels with dichroic mirros.

Key ideas



bandmean wavelength in nm10% trasnmission wavelength (min)10% trasnmission wavelength (max)Compositions
u'348.7301.3391.7KG3(2mm) + UG11(1mm) + Fused Silica (2mm)
Rc656.4580.3729.9OG590(3mm) + Fused silica(2mm)
Ic798.0709.3887.7R-60(5mm) HOYA colored glass

Dichroic mirros

Measured surface (provided by Asahi Spectra)

Corrector lens system and its housing

Expected spot diagram

Boxes in each figure are identical to the pixel size. All of the rms radii fit within the pixel size.

u-band channel

Rc-band channel

Ic-band channel


u-band channel

Rc and Ic-band channel

Dewar window consists of double Fused Sillica with MgF2. A thickness of each is 1mm.

System Diagram

Tracking System

see Activity report


The atmospheric model is "1976 US Standard Asmosphere" with airmass = 1.2, H2O PWV=1.5mm. This atmospheric model was calculated by Prof. Yasuda (Kavli IPMU) using MODTRAN.

Total performance

The lines show the trasmission at the 5100m altitude, the dashed lines show at the filter only and the dashed dotted lines show that at the ground. In this figure, the CCD quantum efficiency (dotted line, blue for uv-enhanced and green for mid-band, -70C) and the dichroic mirros reflection and transmission (not shown here) are included in the resulting curve for 5100 and 0m.
bandmean wavelength in nmGain
``Gain'' is a ratio of integrated transmission curves between 0m and 5100m convolving with the CCD quantum efficiency, Filter transmission, Atmosphere and properties of the dichroic mirros while ``wavelength'' is derived by the filter. For u-band, the UV-enhanced CCD at the 5100m site gains 3.01 times higher efficiency thant the mid-band CCD at the ground.


Here is links to softwares related to this projects. These are still developing.