Kiso Schmidt telescope


Kiso Observatory


Institute of Astronomy, the University of Tokyo


Kiso, Nagano, Japan


35d 47m 50.0s N, 137d 37m 31.5s E (WGS84)


1,132 m

Observatory code

381 / Tokyo-Kiso

Effective aperture

1,050 mm diameter

Focal length

3,300 mm

Focal ratio


Field of View

9 degree diameter



Tomo-e Gozen camera (Sako et al. 2018)

Image sensor


Sensor type

35-mm front-side-illuminated CMOS image sensor with microlens array and AR coated cover glass

Sensor format

2,160 x 1,200 pix/chip (whole area)
2,000 x 1,128 pix/chip (photosensitive area)

Sensor chips

84 chips

Pixel size

19 μm/pix

Pixel scale

1.189 arcsec/pix

Field of view

39.7 arcmin x 22.4 arcmin x 84 chips = 20.8 degree2
Tomo-e Gozen field checker
Distribution of sensors on the sky

Photoelectric conversion efficiency
(pixel aperture ratio x quantum efficiency)

0.72 at a peak wavelength of 500 nm
0.36 at wavelengths of 380 and 710 nm
Wavelength dependence curve

Beam efficiency
(vignetting around the primary mirror)

Degraded at fields outer than 2 deg from the FoV center
Degraded to 0.5 at the outer edge of the FoV


Transparent window

Inverse gain factor

0.23 e-/count in High-gain
0.94 e-/count in Mid-gain
2.4 e-/count in Low-gain

Read noise

2.0 e- in High-gain
4.1 e- in Mid-gain
9.2 e- in Low-gain

Well depth
(linearity < 5%)

6,000 e- in High-gain
25,000 e- in Mid-gain
52,000 e- in Low-gain

Dark current

0.5 e-/sec/pix at 290 K
6.0 e-/sec/pix at 305 K

Thermal design

Passive cooling (no temperature control)

Readout overhead

Zero overhead owing to rolling shutter read out

Data output

Frame rate (max)

2 fps in full-frame read
68.8 fps in partial-frame read
Dependence of readout area

Raw image file

16-bit cube FITS
4.9 MByte/frame (full-frame)

Data production rate (max)

830 MByte/sec = 30 TByte/night (full-frame, 2 fps, 10 hours)

Data quality

Sky background light

50 e-/sec/pix in dark night


3 - 4 arcsec (typ.)

Limiting mag in High-gain
(dark night, PSF FWHM = 3 arcsec,
photometry aperture = 2 x PSF FWHM, S/N = 10)

15.9 mag in 0.1 sec exposure
17.7 mag in 1 sec exposure
19.1 mag in 10 sec exposure

Photometric stability

4 to 30 milli-mag (time scale < 5 sec)
1 to 3 milli-mag (time scale > 100 sec)

Absolute time accuracy of timestamps

±0.2 msec

Stability of frame read time


Survey performance

The number of frames acquired in each area

18 frames at 2 fps

Depth reached in each area
(photometry aperture size = 2 x PSF FWHM, S/N = 10)

17.8 mag (stacked of 18 frames, median value in all lunar phases)

Moving time between areas

10 sec in dithering of 40 arcmin
20 sec in switching of 9 deg

Survey scan rate

2,500 deg2/hour

Data production rate

10 TByte/night

Technical Notes