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Peer-Review Record

Accurate and Rapid Auto-Focus Methods Based on Image Quality Assessment for Telescope Observation

Appl. Sci. 2020, 10(2), 658; https://doi.org/10.3390/app10020658
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Appl. Sci. 2020, 10(2), 658; https://doi.org/10.3390/app10020658
Received: 13 December 2019 / Revised: 9 January 2020 / Accepted: 13 January 2020 / Published: 16 January 2020
(This article belongs to the Section Optics and Lasers)

Round 1

Reviewer 1 Report

This paper presents very practical and efficient auto-focus methods. In order for the paper to be more clear, I recommend to consider the following issues:

 

(1) Title:

There is no reason to say "large aperture telescope system". The ES-DAFW methods is good for "large number of pixels in one image", not for the large aperture. I recommend to delete "large aperture telescope system" or change to other words.

 

(2) 2. Auto-Focus Principle

The important information in this section is the experiment set up.  I recommend to change to section title to "Experiment"

 

(3) Figure 4 and Figure 6

The comparison plots show the efficiency of the AF methods. It would be interesting to show quantitatively. The authors can introduce a kind of efficiency factor = (Max - Min) / (Max + Min). The "Max" and "Min" from the plots of normalized evaluation function value.

 

Author Response

Point 1: Title:

There is no reason to say "large aperture telescope system". The ES-DAFW methods is good for "large number of pixels in one image", not for the large aperture. I recommend to delete "large aperture telescope system" or change to other words.

 

Response 1: In this paper , we wish to solve the fast focusing of the auxiliary telescope module, to achieve the contour capture and centre positioning of the target, not for the astronomical telescope. " large aperture " does deviate from the subject, and change article title to " Accurate and Rapid Auto-focus Methods based on Image Quality Assessment for Telescope Observation " according to your suggestion.

 

Point 2: 2. Auto-Focus Principle

The important information in this section is the experiment set up.  I recommend to change to section title to "Experiment"

 

Response 2: The second part is really more experimental than theoretical. It has been revised to " Auto-Focus Experiment Set" according to your suggestion.

 

Point 3: Figure 4 and Figure 6

The comparison plots show the efficiency of the AF methods. It would be interesting to show quantitatively. The authors can introduce a kind of efficiency factor = (Max - Min) / (Max + Min). The "Max" and "Min" from the plots of normalized evaluation function value.

 

Response 3: Efficiency factors are introduced based on your recommendations, quantifying the data in Figure 4 and listing in Table 6. The data in Figure 6 are quantified in Table 7 by the average slope.

 

 

Thank you sincerely for your suggestions to our article.

 

Reviewer 2 Report

The authors propose a method to improve the quality and speed of auto-focus systems in a electro-optical device, such as
large astronomical telescopes. The proposed method is presented and compared to traditional auto-focusing systems.
It is based on two main principles: first, a sampling of the entire CCD image that avoids the need to locate the
focusing target in a preliminary stage and, second, an adaptive method based on a dynamic focusing windowing that
prevents the need of an initial setup of the focusing region. The idea is to identify ROI pixels from background
due to their higher change of IEF value and by increasing the de-focusing localized precision through
a sub-window matrix splitting the image, thus improving the quality and speed of auto-focusing corrections.

However, the idea to build a sub-pupil matrix where to estimate and correct a well-localized de-focus is not new and it
is one of the well known mechanisms at the base of the so-called "active optics" technology, broadly adopted in new generation
astronomical observing devices in the last 20 years. Moreover, in the paper a very weak point is the missing consideration about the primary
mirror correction requirements to achieve the proposed solution on large telescopes in a practical way and to probe the
realistic application of their method on new generation observing instruments.
Furthermore, active optics systems were already proposed and in many cases already mounted on real large telescopes, able
to cope with first order aberrations, such as the windowed de-focusing corrections. See for example Schipani et al. 2006,
2007 and a complete review of technological solutions in Proceedings of the International Astronomical Union Symposium S232,
ISSN 1743-9213, Cambridge University Press, 2006.

In order to make more interesting and pragmatic their solution, the authors should discuss technological aspects related to
the realistic usefulness of the proposed method in case of large telescopes, by probing the compatibility with hardware
mechanisms able to reflect the theoretical approach in case of large primary mirrors and to compare de-focusing performances
with the solutions proposed in literature, such as active optics systems.

In the following a series of linguistic and syntax typos corrections:

ABSTRACT

- row 19: ...scenarios. It is demonstrated that the...

INTRODUCTION

- row 39: ...to increment the cost...
- row 40: ...this limits -> thus limiting
- row 44: ...telescope systems,
- row 45: of astronomy -> of Astronomy
- row 46: ...in this paper, we investigate -> we analyzed (avoid repetition of the word investigate)
- row 47: of the image estimation

SECTION 2

row 64: repetition of "investigated". The investigated EOTS... -> remove "investigated"
row 66: ...Cassegrain telescope involved a -> Cassegrain telescope composed by
row 69: of the telescope there is a CCD...
row 76: program has an estimation -> program performs an estimation
row 77: counter-clockwise direction. Then, a mechanical...
row 84: ...the focus concrete process -> the concrete focus process
row 86: as figure 2 -> are shown in figure 2
row 87: length, and record the -> length, recording the
row 87: maximum value the stepper... -> maximum value. The stepper...
row 90: make the knob rotate -> the knob is rotated (remove "make")
row 91: is repeated until
row 92: stepper motor. Then, the auto...

SECTION 3

row 94: Different scenes, as captured by EOTS, ...
row 104: ...in spatial and frequency domains.
row 129: correct the sentence as follows -> "as only a small part of the object in the target."
row 131: ..so it may cause that part...
row 140: ...gradient information of the...
formula (7) : explain that M and N are the image dimensions
row 149: redundant repetition of words. Replace as "including 4 and 8 domain Laplace templates."
row 149-150 replace the sentence as follows: "In order to maximize the gradient information of the image, 8 domain
Laplace templates are used in the experiment."
row 170: ...indicating the exist of -> indicating the presence of

SECTION 4

row 204: ...focusing window. We the pixels -> focusing window. The pixels

Author Response

Thank you sincerely for your suggestions to our article. The imaging blur caused by defocusing is really the key problem in the astronomical telescope system. In this paper, we wish to solve the fast focusing of the auxiliary telescope observation, and to achieve the contour and centre positioning of the target. We pays more attention to the algorithm technology in the process of auto focusing. We change article title to " Accurate and Rapid Auto-focus Methods based on Image Quality Assessment for Telescope Observation ".

       Our article does have some errors in linguistic and syntax typos. To the best of our ability, we have modified the grammatical issues in our article based on your comments. Thank you very much for giving us very detailed amendments in this regard, which is very helpful to us.

Round 2

Reviewer 2 Report

The authors adjusted the manuscript that now can be published, since it is mostly referred to auxiliary, small size, instruments.

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