Optical–digital joint design of refractive telescope using chrom...
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Optical–digital joint design of refractive telescope
using chromatic priors
Jingang Zhang (张金刚)
1,2,†
, Yunfeng Nie (聂云峰)
3,
*
,†
, Qiang Fu (付 强)
4
,
and Yifan Peng (彭祎帆)
5
1
Key Laboratory of Computational Optics Imaging Technology, Chinese Academy of Sciences, Beijing 100094, China
2
University of Chinese Academy of Sciences, Beijing 100049, Beijing
3
Brussel Photonics, Department of Applied Physics and Photonics, Vrije Universiteit Brussel, 1050 Ixelles, Belgium
4
King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
5
The University of British Columbia, Vancouver V6T 1Z4, Canada
*Corresponding author: ynie@b‑phot.org
Received October 15, 2018; accepted January 30, 2019; posted online April 30, 2019
The conventional optical system design employs combinations of different lenses to combat aberrations, which
usually leads to considerable volume and weight. In this Letter, a tailored design scheme that exploits state-of-
the-art digital aberration correction algorithms in addition to traditional optics design is investigated. In par-
ticular, the proposed method is applied to the design of refractive telescopes by shifting the burden of correcting
chromatic aberrations to software. By enforcing cross-channel information transfer in a post-processing step, the
uncorrected chromatic aberrations are well-mitigated. Accordingly, a telescope of F-8, 1400 mm focal length,
and 0.14° field of view is designed with only two lens elements. The image quality of the designed telescope is
evaluated by comparing it to the equivalent designs with multiple lenses in a traditional optical design manner,
which validates the effectiveness of our design scheme.
OCIS codes: 220.4830, 220.1010, 200.4740, 100.2980.
doi: 10.3788/COL201917.052201.
Telescope objectives are frequently applied in remote
sensing, photography, and security surveillance applica-
tions. The performance of refracting telescopes is
typically limited by ch romatic aberrations that are inher-
ently originated from the long focal length
[1]
.In
order to correct the i nduced chromatic aberrations, the
most common methods are using cemented doublets or
triplets that are composed of two or three optical mate-
rials with anomalous dispersion, such as CaF
2
and
FK71
[2]
. However, these carefully designed telescopes
are usually expensive, troublesome to manufacture due
to fragility, unstable in harsh environments, and unavail-
able in large apertures
[3]
. McCarthy
[4]
and Wynne
[5]
pro-
posed special optical layouts to eliminate longitudinal
chromatic aberrations with normal glasses. Both systems
consist of two or more widely spaced lens groups, which
are not suitable for remote sensing and other narro w
space occasions. Besides, these optical systems still suffer
from lateral chroma tic aberrations and other hig h-order
monochromatic aberrations. Yang et al.
[6]
introduced a
four-group design, where most aberrations are carefully
removed. Nevertheless, the design is still too long with
easily more than seven components, increasi ng the manu-
facturing and assembly costs.
With the maturing of diffractive optical elements
(DOE) in design theory and manufacturing, they are more
and more frequently used to decrease secondary spectra
based on their particular dispersion feature. These designs
can have much larger apertures compared to refractive
counterparts, yet the good image quality and high
transmission can only be achieved in a narrow-band
spectrum
[7]
. Some reflecting telescopes are also subject
to chromatic aberrations due to the existence of corrective
lenses in the front or rear group, for example, the famous
pan-Cassegrain system, where the secondary spectrum
can be considerable
[8]
.
We propose a tailored design scheme that utilizes the
benefits of a digital imaging processing technique to alle-
viate the burdensome chromatic aberration correction
from optical design. The optical–digital design chain
includes firstly an optical design optimization procedure
to obtain the optical layout with quasi-monochromatic
imaging performance. After that, digital processing is
implemented to recover the sharpness of other color
channels to fulfill a broad-band design. Results show that
a comparable performance can be achieved in a two-lens
design with our method when compared with its classic
multi-lens counterparts.
In classic Fourier optics, the imaging systems are con-
sidered as linear systems, where the point spread function
(PSF) distribution is regarded as spatially invariant
[9]
,at
least within a local patch of a certain size. Under this
assumption, the noise has a devastating influence when
recovering the image. We consider the following well-
known image formation:
z ¼ AðαÞx þ n; (1)
where α represents different optical aberrations, and AðαÞ
are the PSFs in matrix form, x is the target scene in vector
COL 17(5), 052201(2019) CHINESE OPTICS LETTERS May 10, 2019
1671-7694/2019/052201(4) 052201-1 © 2019 Chinese Optics Letters
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