Through a Blue Lens
Through a Blue Lens is a documentary film produced by the National Film Board of Canada.
 The film follows interactions between police officers and drug addicts and documents the extreme poverty and suffering many addicts endure.
Box camera
A box camera is a simple type of camera, the most common form being a cardboard or plastic box with a lens in one end and film at the other.
 They were very popular in the late 19th and early 20th centuries.
 The lenses are often single element designs meniscus fixed focus lens, or in better quality box cameras a doublet lens with minimal (if any) possible adjustments to the aperture or shutter speeds. Because of the inability to adjust focus, the small lens aperture and the low sensitivity of the sensitive materials available, these cameras work best in brightly lit day-lit scenes when the subject is within the hyperfocal distance for the lens and of subjects that move little during the exposure.
 Eventually, box cameras with photographic flash, shutter and aperture adjustment were introduced, allowing indoor photos.
A-scan ultrasound biometry
A-scan ultrasound biometry, commonly referred to as an A-scan (short for Amplitude scan), is routine type of diagnostic test used in optometry or ophthalmology.
 The A-scan provides data on the length of the eye, which is a major determinant in common sight disorders.
 The most common use of the A-scan is to determine eye length for calculation of intraocular lens power.
 Briefly, the total refractive power of the emmetropic eye is approximately 60.
 Of this power, the cornea provides roughly 40 diopters, and the crystalline lens 20 diopters.
 When a cataract is removed, the lens is replaced by an artificial lens implant.
 By measuring both the length of the eye (A-scan) and the power of the cornea (keratometry), a simple formula can be used to calculate the power of the intraocular lens needed.
 There are several different formulas that can be used depending on the actual characteristics of the eye.
 All the information here is not valid for medical purposes.
Anti-scratch coating
An anti-scratch or scratch-resistant coating is a film or coating that can be applied to optical surfaces, such as the faces of a lens or photographic film.
 The coating does not interfere with how the lens functions and does not affect vision, but creates a permanent bond with the lens that reduces the appearance of hairline scratches which is common to eyeglass lenses.
 Though an anti-scratch coating is not 100% scratch-proof, it helps to prevent minor scratches that can easily happen to a regular lens.
 These minor scratches can damage the surface of the lens and impair vision.
 An anti-scratch coating acts as a protective layer thus making the lenses more durable and safe.
Fungal contamination of contact lenses
Microbial corneal infection is the most serious and "most common vision threatening" complication of contact lens wear, which is believed to be strongly associated with contact lens cases.
 Such infections "are being increasingly recognized as an important cause of morbidity and blindness" and "may even be life-threatening."
 While the cornea is believed to be the most common site for fungal eye infections, other parts of the eye such as the orbit, sclera, eyelids, and more may also be involved.
 Contact lens cases are recognized as a "potential source of pathogens associated with corneal ulcers" and according to Moorfields Eye Hospital, contact lens wear is “the most prevalent risk factor for new cases of corneal ulcers.”
 Contaminants "isolated from contact lens associated corneal ulcers have often been shown to be" the same as found in the patient's contact lens case, thus providing evidence contaminated contact lens cases may be a "replenishable source of pathogenic microbes."
Intraocular lens
Intraocular lens (IOL) is a lens implanted in the eye as part of a treatment for cataracts or myopia.
 The most common type of IOL is the pseudophakic IOL.
 These are implanted during cataract surgery, after the cloudy eye's natural lens (colloquially called a cataract) has been removed.
 The pseudophakic IOL provides the same light focusing function as the natural crystalline lens.
 The second type of IOL, more commonly known as a phakic intraocular lens (PIOL), is a lens which is placed over the existing natural lens, and is used in refractive surgery to change the eye's optical power as a treatment for myopia, or nearsightedness.
 IOLs usually consist of a small plastic lens with plastic side struts, called haptics, to hold the lens in place within the capsular bag inside the eye.
 IOLs were conventionally made of an inflexible material (PMMA), although this has largely been superseded by the use of flexible materials.
 Most IOLs fitted today are fixed monofocal lenses matched to distance vision.
 However, other types are available, such as multifocal IOLs which provide the patient with multiple-focused vision at far and reading distance, and adaptive IOLs which provide the patient with limited visual accommodation.
Capsulotomy
Capsulotomy is a type of eye surgery in which an incision is made into the capsule of the crystalline lens of the eye.
 In modern cataract operations, the lens capsule is usually not removed.
 The most common forms of cataract surgery remove nearly all of the crystalline lens but do not remove the crystalline lens capsule (the outer “bag” layer of the crystalline lens).
 The crystalline lens capsule is retained and used to contain and position the intraocular lens implant (IOL).
Plasmat lens
The Plasmat lens is a widely used and long-established lens type invented by Paul Rudolph in 1918, especially common in large-format photography.
 It provides high correction of aberrations with a moderate maximum aperture (e.g. f/5.6 ).
 It is a specific instance of the Dagor type double-meniscus anastigmat.
 Double-meniscus anastigmats use widely separated positive and negative surfaces, generally thick meniscus lenses, to achieve a flat field.
 The most basic form is two sharply curved meniscus elements located symmetrically about a stop.
 Further refinement of the form replaces the two simple meniscus lenses with achromats for chromatic correction.
 The Dagor type further refines these achromats into triplets with the following design parameters: a high-index, doubly convex (DCX) lens cemented to a medium-index, doubly concave (DCV) lens cemented to a low-index meniscus lens.
 Up to this point, all refinements have maintained symmetry about the stop.
 The Plasmat further refines the Dagor form by uncementing the meniscus, allowing for placement away from the first two elements and removing the criterion of symmetry.
Reisekamera
The Reisekamera, meaning a "travel camera", is a large-format wooden bellows tailboard view camera of almost standardised design, unlike the much lighter and more flexible field camera, but not as cumbersome as the studio camera.
 A sturdy tripod is always brought along, but it might just as well be placed on a tabletop.
 It has equally sized rectangular front and back panels on a full-width double-extension baseboard that is hinged near the front.
 The front panel, holding the lens plate, has horizontal and vertical movements, while the back is tilt-suspended on brass standards running on brass tracks on either side of the baseboard, providing rack and pinion focusing on the film plane.
 An almost non-tapering calico double-extension bellows is employed; allowing the projected image to freely reach the photographic plate regardless of lens offset position.
 The camera folds flat, after the back panel is brought forward to the lens panel, by folding the hinged base board up, and thus conveniently protecting the focusing screen.
 For insertion of the wooden dark slide plate cassette, the hinged focusing screen is swung up and away.
 The Reisekamera was made available for several plate sizes; most common are the 13×18 cm, 18×24 cm and 24×30 cm versions.
 Shutter and lens were normally not part of the original delivery.
 However, some were made available with a spectacular focal-plane shutter, recognisable by the brass mechanisms either side of the back panel.

Question: What do Through a Blue Lens and There Is No Authority But Yourself have in common?
Answer: documentary