|
The optical design for the One Metre Initiative
is breaking new ground in the world of optics by being the largest
field prime focus telescope in the world. The corrector/field
flattener is unprecedented as it will deliver a highly corrected
5 square degrees field of view. A 4 lens design was chosen with
fused silica glass on the first three elements and CaF2 for the
final element. The design uses spherical surfaces except for the
surface facing the image sensor which is aspherical. The design
offers 0.39"/0.7" centre/edge with 80% energy encircle
diameters (r', 0.76"/pixel, 9um pixel).
The OMI optical design uses 4 lens with L1, the
field lens, has a diameter of 345 mm.
Detail of the OMI 4-lens optical design.
The OMI optician commented:
"This will be the largest primary field corrector in the
world."
and...
"I do not know any other primary corrector that has such
a large field of view."
To Clarify: The optical designer knows of no other
telescope in the world with such a wide field of view from a prime
focus-based telescope design. LSST will have a 10 square degree
field but it uses "three" mirrors and a corrector in
a pseudo Schmidt Camera/Cassegrain configuration. Even when LSST
comes on line, as long as no other telescope has come on line
with a 5 square degree field or larger in a prime focus configuration,
the 1m f2.5 we are working toward will still hold its title and
distinction.
|
Field
|
u'
|
g'
|
r'
|
i'
|
z'
|
|
degrees
|
arcsec
|
arcsec
|
arcsec
|
arcsec
|
arcsec
|
|
0.00
|
1.758
|
0.531
|
0.372
|
0.373
|
0.571
|
|
0.173
|
1.780
|
0.552
|
0.366
|
0.394
|
0.625
|
|
0.346
|
1.825
|
0.609
|
0.343
|
0.405
|
0.691
|
|
0.518
|
1.842
|
0.652
|
0.346
|
0.444
|
0.757
|
|
0.691
|
1.799
|
0.665
|
0.403
|
0516
|
0.787
|
|
0.864
|
1.684
|
0.721
|
0.525
|
0.625
|
0.808
|
|
1.037
|
1.591
|
0.819
|
0.713
|
0.804
|
0.919
|
|
1.209
|
1.645
|
0.971
|
0.897
|
0.959
|
0.992
|
|
1.382
|
1.837
|
1.035
|
0.927
|
1.015
|
0.992
|
|
1.555
|
2.058
|
0.943
|
0.705
|
0.994
|
1.138
|
|
Average
|
1.782
|
0.75
|
0.560
|
0.653
|
0.787
|
OMI optical performance table, 80% energy encircle
diameters (arcsec) vs. field (degrees).
OMI Spot diagram curves bases on 80% encircle energy.
OMI Spot diagram with radii data.
|
Lens
|
Glass
|
Diametre
|
Design
|
Total Length (mm)
|
|
|
|
mm
|
|
Corr./Effec.
|
|
L1
|
Fused Silica
|
345
|
Spherical
|
690/2453.95
|
|
L2
|
Fused Silica
|
215
|
Spherical
|
|
|
L3
|
Fused Silica
|
203
|
Spherical
|
|
|
L4
|
CaF2
|
203
|
Spherical/Aspherical
|
|
Lens topology
Vignetting
The vignetting, reduction in illumination at the
edge of the field, is only 6% at 1.56 degrees from the centre.
Next: The Mount
|
