ENERGY
a proposal for a Multi-channel
Cmos Camera
hn
e-
F. Pedichini, A. Di Paola, R. Speziali
INAF Oss. Astr. Roma
What is multi-channel imaging?
The most standard duty of an astronomer
simply : Multi Band Photometry
How to do it?
The 3 most used
technologies:
• 1- an old, but good, FILTER WHEEL + 1
CCD imager
•2- a MOSAIC FILTERED CCD imager
•3- a DICROICH focal plane
splitter + several CCD imagers
All of these items deserve a...
deep comparative analisys !
an old, but good, FILTER WHEEL
+ 1 CCD imager
Imager
...101010
00111....
Has been used since the first digital imager, with great results,
low cost, simple mechanics, user selectable bands and thx. to
modern CCDs also a very good Q.E.
......but......
different bands are exposed and acquired at different times
due to detector readout time and filters set up time
a MOSAIC FILTERED CCD
imager
....RGBRGB.... matrix
filter
widely used in low cost tv cameras, digital
photography apparatus and amateur astronomy color
imagers with all the bands taken during the same
exposure
.....but.....
no user selectable bands, low Q.E. (quite impossible
to be used with back illuminated detectors) and the
bad MOIRE effect...
the MOIRE effect...
the color of each pixel is function of the signals of the
nearest ones producing nice
on
sharp edges....!
astronomers dont’LIKE!
a DICROICH focal plane splitter
+ several CCD imagers
Imager
Imager
...101010
00111....
Imager
...101010
00111....
...101010
00111....
sometime used in astronomy
with the best Q.E. and time
sincronicity in each channel
....but....
complex, expensive and
polarization & f# sensitive
polarization & f# sensitive
• dicroichs are made up by dielectric layers and
partially polarize the reflected and transmitted
beams
• best performances about field uniformity need
collimated beams so a collimator and several
camera optics must be added in the imager
optical train
• often the weight and size of a “dicroich”
imager make it impossible to fit some
telescope focal planes as in the case of
Schmidts or fast prime foci
and now we go to a comparative table...
comparative table....
Type
Q.E.%
Sampling
Syncro
Complexity
Filter
Whell
90
Good
No
Standard
Mosaic
Filter
20-30
Moire
Yes
Low
Dicroich
80-90
Good
Yes
High
........is the world of C-MOS helping us with a fourth chance?
http://www.foveon.com
in this detector each pixel outputs
R,G and B signals with all the nice features of
a CMOS “on chip camera”
•about 10Mpix in three layers
•low power
•on chip 12bit ADC
•windowing and binning
•4 f.p.s.
•less than 30e- RON
foveon phisycs:on silicon
“dicroich”
• red photons are
deep penetrating the
silicon
• green photons make
photoelectrons
midway
• blue photons
interact early.....
foveon bands:
1.2
BJ
1
VJ
RJ
0.8
0.6
0.4
0.2
• bands are not user
selectable
• how do they compare
to Johnson filters
• what can we do with
them in astronomy?
0
0.3
0.4
0.5
0.6
0.7
0.8
0.9
-0.2
0.4
Bfov
0.35
Vfov
Rfov
0.3
0.25
0.2
0.15
0.1
0.05
0
0.3
-0.05
0.4
0.5
0.6
0.7
0.8
0.9
Black Bodies simulations:
Teff
20000
15000
10000
8000
6000
4000
2000
B
V
7.3
7.99
9.24
10.13
11.57
14.4
22.58
7.57
8.18
9.24
9.98
11.16
13.47
20.22
R
7.74
8.29
9.24
9.89
10.91
12.87
18.5
Bf
7.47
8.11
9.24
10.02
11.27
13.64
20.05
Vf
7.61
8.2
9.24
9.95
11.09
13.24
19.22
Rf
7.75
8.3
9.24
9.89
10.9
12.82
18.24
25
B
V
20
R
Bf
15
Vf
Rf
10
5
Teff
0
0
5000
10000
15000
20000
25000
BB spectra from
2000 to 20000 K
convolved with BVR
Jhonson and BVR
Foveon converted
to magnitudes
reduction to Johnson....
it is possible using instr. color index Vf-Rf or Bf-Vf and
a second order polinomya.
error is 0.01 mag.
V-Vf = 0.7818(Vf-Rf)^2 + 0.2571 (Vf-Rf)- 0.0051
3
B-Bf
R2 = 0.9998
V-Vf
2.5
R-Rf
Poli. (B-Bf)
2
Poli. (V-Vf)
Poli. (R-Rf)
1.5
R2 = 0.9992
1
0.5
R2 = 0.9989
0
-0.2
0
-0.5
0.2
0.4
0.6
0.8
1
Vf-Rf
1.2
Energy camera:
•Uses Foveon M10 x3 CMOS
•2200 x 1500, 9 micron pixels
•3 bands, 4fps
•about 25 arcmin2 @ 12 m focal lenght
•0.15 arcsec/pixel
•30 e-RON
•0.25 seconds read out time
•no shutter needed
LBC comparison on a mag 14 star:
Target:
star field BVR
fast photometry
at S/N = 100 to detect
light transients
SKY 1”seeing
~21mag/arcesc^2
CCD:
exp. 0.013 sec
QE 90%
2e/adu
RON 5 e-
Time for 3 bands:
exp. 3x0.013 sec
filter 3x1 sec
readout 3x1sec
total ~3 sec
Telescope:
Mirror 8.2m. 1.4F#
(prime focus camera)
Energy:
exp. 0.04 sec
QE 30%
5e/adu
RON 30 e-
Time for 3 bands:
exp. 1x0.04 sec
filter 0 sec
readout 1x0.25sec
total ~0.3 sec
Both cameras:
9 micron pixels
about 4Mpixel
LBC comparison on mags @ S/N 100:
12
3.9Hz
3.5Hz
10
CCD exp
Energy exp
8
2.9Hz
2Hz
6
1.1Hz
4
0.5Hz
2
0
11
13
15
17
19
21
Mag 23
ENERGY @ 60/90/180 Schmidt:
On a smaller telescope at the resolution of
1”/pixel the field is 1180 arcmin^2.
Energy becomes a:
multiband GRB Hunter on raw satellite triggers
Hz
4.5
4.0
3.5
3.0
S/N=100
2.5
S/N=10
2.0
1.5
1.0
0.5
0.0
4
6
8
10
12
14
16
Mag18
2nd comparative table....
Type
Q.E.%
Sampling
Syncro
Complexity
Filter
Whell
90
Good
No
Standard
Mosaic
Filter
20-30
Moire
Yes
Low
Dycroich
80-90
Good
Yes
High
CMOS
Foveon
~30
Good
Yes
Low
open discussions:
•1) Is it useful in astronomy?
•2) Can Foveon modify the shape of the bands?
•3) Will we have more than 3 on-chip bands in the future?
•4) Can Foveon technology used on back ill. detectors?
•5) Can Foveon technology join CCDs?
the end.....
Energy
is a
Multi channel camera
or...
2
Mc