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Spie Press Book

The Proper Care of Optics: Cleaning, Handling, Storage, and Shipping
Author(s): Robert Schalck
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Book Description

If you want the best performance from your optics, they need to be properly maintained. This book describes the cleaning, handling, and storage methods used by professional technicians to keep optics in top condition. It is written for a diverse audience, from first-time optical cleaners to assembly technicians and seasoned engineers looking to expand their repertoire. In the lab or in the field, you'll find the right technique to protect your equipment from harm. Reference lists of tools, solvents, and suppliers are provided to help you find solutions quickly.

An updated version of the book is now available: The Proper Care of Optics: 2019 Update


Book Details

Date Published: 27 March 2013
Pages: 236
Volume: PM233

Table of Contents
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Chapter 1 Introduction
1.1 Safety
1.2 Optical Materials: Glass, Coatings, Plastic, and IR
1.3 When to Clean

Chapter 2 Cleaning Tools and Work Area
2.1 Equipment for Cleaning Optics
      2.1.1 Worktable
      2.1.2 Laminar flow bench
      2.1.3 Lighting
      2.1.4 Lighting types
      2.1.5 Compressed air and gas
2.2 Cleaning Tool List
      2.2.1 Cleaning-tool usage summary
      2.2.2 Soft brushes
      2.2.3 Gloves and finger cots
      2.2.4 Cleaning solvents and materials list
      2.2.5 Solvent dispensers
      2.2.6 Solvents
      2.2.7 Personal protective equipment: gloves, cots, face mask, head cap, and lab coat
2.3 Applicator Types
      2.3.1 Hand technique for cotton- and foam-tip applicators
      2.3.2 Folding lens tissue
      2.3.3 Hand techniques for folded tissues or wipes

Chapter 3 Inspecting Optics
3.1 The Inspection Process
      3.1.1 Types of contamination
      3.1.2 Scratch and dig: a history
      3.1.3 Visual method: using the unaided eye
      3.1.4 Using the eye loupe magnifier
      3.1.5 Using a low-power and Nomarski microscope
      3.1.6 Map making: visual and digital methods
      3.1.7 Mirror coating
      3.1.8 Antireflection coating
      3.1.9 Digital microscopes

Chapter 4 Cleaning Techniques for Small and Large Optics
4.1 Small Optics
4.2 Inspecting Large Optics
      4.2.1 Large optics: hand-cleaning techniques
      4.2.2 Large lens
      4.2.3 Large mirror
      4.2.4 Large window
      4.2.5 IR optics: transmission and reflective

Chapter 5 Special Cleaning Processes
5.1 Drag Method
5.2 Strip-Coating Cleaning
5.3 Cleaning Plastic Optics
5.4 Chalk Cleaning
5.5 CO2 Cleaning
5.6 Ultrasonic Cleaning
5.7 Carbon-Tip Cleaning
5.8 Spin Cleaning
5.9 Automatic Cleaning System: A Reference

Chapter 6 Cleaning Optical Systems and Instruments
6.1 Techniques for Instrument Cleaning
      6.1.1 How to view instruments
      6.1.2 Marking methods: identification
      6.1.3 Hand tools for instruments
      6.1.4 Instrument and optical-system cleaning
6.2 Internal Optics Cleaning
      6.2.1 Instrument Windows and View Ports
      6.2.2 Disassembling an instrument
      6.2.3 Refractor telescope
      6.2.4 Reflector telescope
      6.2.5 Catadioptric optical system
      6.2.6 Binoculars and monocular
      6.2.7 Light microscope
      6.2.8 Eyepiece
      6.2.9 Camera: single-lens reflex and video
6.3 Non-instrument Cleaning and Instrument Protection
      6.3.1 Vehicle and Building Windows: A Reference
      6.3.2 Metal optics
      6.3.3 Covering optical instruments
      6.3.4 Video CCD and CMOS sensor chips
      6.3.5 Cleaning microscope slides
      6.3.6 Eyeglasses: a reference

Chapter 7 Tricks of the Trade
7.1 Edge Cleaning
      7.1.1 Surface protection
      7.1.2 Wood stick tools
      7.1.3 Soap and detergent
      7.1.4 "Huffing" and skin oil
7.2 Black Paint and Black Pen Ink for Edge Blackening
      7.2.1 Blackening the edge of a lens, window, or prism
      7.2.2 Painting a nonoptical surface with black paint
      7.2.3 Blackening the edge with a rotating spindle
7.3 Removing RTV Silicone Rubber
      7.3.1 Removal of cured glue and cement from an optical surface
      7.3.2 Removing aluminum coating with liquid etch: a reference
      7.3.3 Lighthouse lenses: a historical reference

Chapter 8 Handling Optics
8.1 Tweezers and Hemostats
8.2 Special Tweezers
8.3 Suction and Vacuum Cups
8.4 Using Trays to Handle Optics
8.5 Storage Box and Cabinet Types

Chapter 9 Protection Methods for Optics
9.1 Tissue
9.2 Envelopes
9.3 Storage Containers

Chapter 10 Storing Optics
10.1 Short-Term Storage of Optics
10.2 Long-Term Storage of Optics

Chapter 11 Shipping Optics
11.1 Cardboard, Plastic, and PET/G Boxes
11.2 Cardboard Shipping Containers
11.3 Clamshell Shipping Containers
11.4 Other Types of Shipping Boxes

Chapter 12 R&D Laboratory Cleaning Kit

Chapter 13 Cleaning Optics in the Field
13.1 Field Cleaning Kit
13.2 Field Setup and First Process
13.3 Outdoor Lighting
13.4 Field Work Area

Chapter 14 Resources
14.1 Suppliers of General Cleaning Products
14.2 Suppliers of Cleaning Tools
14.3 Suppliers of Storage Items
14.4 Shipping Suppliers

Quick Cleaning Reference


Of all the human senses, sight is the dominant one. The human brain receives most of its information in the form of visual stimulus, and optics plays an important role in delivering that information. Take, for example, a person using a digital camera to shoot a picture of the Grand Canyon. A person's eyes perceive the scene first, possibly while wearing eyeglasses, contacts, or sunglasses. Photons (light) from the sun are reflected or absorbed by the pigments in the canyon walls. The photons hit the first surface of the camera lens and are then refracted several times by the internal optical lenses. The collections of photons are focused on the surface of the imaging chip and stored, to be retrieved by a computer or printed onto paper. On the computer, the image is displayed on a screen, observed, and adjusted. The image is then sent to a device to be printed or projected using internal optics. Fiber optic cables send the image electronically.

We use optics every day, from the moment we wake up until we retire for the night:

* An alarm clock displays the time using lenses and LEDs;
* We view our reflection in a bathroom mirror;
* The headlights and taillights in vehicles have lenses and reflectors;
* When we drive down the road, reflectors guide us and keep us on the correct side of the road;
* Traffic lights control the flow of traffic, streetlights light the roadways, and video cameras monitor traffic;
* Digital projectors are used for meetings, computer screens display information, stage lighting in theaters use Fresnel lenses, and a microscope allows us to view microbes.

This book describes the cleaning, handling, and storage methods used by professional technicians and engineers to maintain optics. It is written for a diverse audience, from a first-time optical cleaner to a seasoned engineer who is looking for an old optical trick used many years ago. There are many ways to clean optics; some are learned from experience and/or failure. A few people will discover that these methods may differ from what they learned and question them. How to clean optics has always been a challenging and controversial subject. Searching the Internet will yield hundreds of articles and videos that claim to know the best methods.

Cleaning is one of the procedures used to keep an optical instrument at its peak performance. Dust, fingerprints, and stains can degrade even the best optical system, resulting in poor imaging. Failing to remove certain types of contamination in a timely manner can damage the optics or optical coatings. Cleaning consists of a series of simple, easy steps. To master these steps, all that is required is frequent practice.

Cleaning methods have improved since the 1960s with the start of the manufacturing of critical optics for aerospace applications and lasers. Surface quality specifications became tighter, and a so-called "commercial type finish" is no longer the norm. It is now common to have specifications for scratch and dig ranging from 40-20 to 10-5. Practically all particles must be removed to avoid interference with the image quality or the possibility of damage to critical electronics. Even partial monolayers of real contaminants can compromise coating performance and adherence. Newer materials and methods were developed to meet these new demands.

The storage of optics and optical systems is very important to maintain the optical surface cleanliness. Proper storage techniques for mounted and unmounted optics are discussed; storage for complex optical instruments (e.g., video cameras, film cameras, etc.) are not covered, although similar procedures can be used. Handling optics is considered only as it applies to cleaning, protection, and storage. Other considerations such as shipping, assembly, and disassembly are also discussed.

Robert Schalck
February 2013

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