In this second part of my “revised” instructional series, we’ll discuss … the “Lens”.
In the previous post we said that the all important “frame” is the stage with which we capture and display images or events to an audience. That being said, the “lens” is the glass that not only seperates but also to a degree, impacts how the viewer percieves the events that are happening in the “frame”.
Before delving into the details, it would be difficult to discuss lenses without first discussing some basic concepts regarding lenses.
FoV (Field-of-View) The observable expanse visible through an optical instrument at a given time. In simple terms, its the how much a lens can ‘see’.
Focal Length Technically speaking, the focal length is the measurement (expressed in mm) of the distance between the lens and the capturing device (film or sensor) when the subject is in focus. Practically speaking, the focal length of a lens lets us know the FoV (Field-of-View) of a lens. The smaller the focal length, the wider the FoV and conversely, the larger the focal length, the narrower FoV.
DoF (Depth-of-Field) The distance from the closet and farthest objects that appear to be in focus is referred to as the Depth of Field. The amount of DOF is a result of 1) lens focal length, 2) lens aperture, and 3) subject distance to lens.
Aperture Opening which allows light to pass through a lens. This opening can be expanded (to allow more light) or constricted (reduce amount of light), altering the exposure (brightness) of an image. The size of the opening is often expressed numerically as “f-stops” or “t-stops” (for all intents and purposes these are the same thing). This is not a physical measurement, but rather a ratio, expressing the lens’s focal length in relation to the diameter of the aperture. Practically speaking, the smaller the number, the wider the opening, thus allowing more light to pass through lens. Aperture effects DoF in that a wider aperture results in less DoF, or a narrow focus range.
Bokeh “Bokeh” refers the visual quality of the out-of-focus areas of a photographic image, especially as rendered by a particular lens.
With those concepts in mind, the “Lens” is quantified by OPTICAL PROCESS, the “LOOK”, COMPATIBILITY, and ERGONOMICS.
OPTICAL Process
OPTICAL Process refers to the primary optical design used in a lens, either SPHERICAL or CYLINDRICAL, or more commonly referred to as ANAMORPHIC. This subject was previously discussed in this post. Essentially, the type of optics used in a lens impacts how it manipulates light and thus impacts the viewer experience. Below is an example of a scene recorded using Spherical and Anamorphic lenses. Note the visual differences (round vs oblong “bokeh”, Depth-of-field, dimensionality in the face, etc).
“I like the immediacy of spherical lenses, cause I like being close to the subject. I like the feeling of the background staying more present and more sharp. And with anamorphic it tends to push the backgrounds away and put them out of focus.” – Roger Deakins ASC
THE “LOOK”
“LOOK” refers to the over-all aesthetic characteristics of a lens. Apart from the aesthetic differences associated with the optical process, the “Look” of a lens can be quantified by PERSPECTIVE, COLOR, CONTRAST, and TEXTURE.
PERSPECTIVE referes to the visual transformation or change of an image as it viewed through different lens focal lengths. This primarily affects three things areas: COMPRESSION, SHAPE, and PRESENCE.
COMPRESSION is, “phenomenon of background elements appearing larger than they actually are – hence the scene becomes “distorted” since those background elements appear closer and larger than they are in real life”.
SHAPE refers to the over-all appearance of an object when viewed through varying focal lengths.
PRESENCE refers the sense of location a particular focal length can impute to the audience.
The second quantifier of the ‘LOOK’ of a lense is COLOR. Color refers to over-all color cast lens may apply to the image. Often described as WARM, COOL, or NEUTRAL.
The third quantifier for the ‘LOOK’ of a lens is CONTRAST. Contrast is the over-all manner in which a lens captures varying levels of brightness and the transitions in between. High-Contrast lenses tend to exaggerate the differences, resulting in a “punchier” image while low-contrast lenses, tend to minimize them, resulting in a “flatter” or monotone image.
The fourth quantifier for the ‘LOOK’ of a lens is TEXTURE. Texture refers to a lenses ability to not only capture detail (resolution) but also the manner in which it does so. A lens can be sharp or it can ‘soft’ (yet still be in focus). Additionally, this could also apply to how a particular lens renders out-of-focus objects or “bokeh”.
Interestingly, manufacturers will often use the last three quantifiers to differentiate or market their products. In the example below look for the differences in color, contrast, and texture.
“The Cooke ‘look’ is not only renowned but coveted by many top DP’s. The look has been described as creamy, warm, luscious with excellent sharpness while retaining beautiful bokeh and falloff. ” — Christopher Barrett
COMPATIBILITY
COMPATIBILITY refers to the ability to match a lens to a capture device. The main areas of consideration are IMAGE CIRCLE and LENS MOUNT.
Essentially, a lens works by capturing the reflected light of objects and projecting them back towards a capture device (like a film frame or sensor). The over-all size of the projection is the IMAGE CIRCLE. In practical terms, the Image Circle has to be of sufficient size to cover the capture format (physical size of the capture device). (Resource: https://www.hdvideopro.com/columns/help-desk/sensors-circles/2/)
After the Image Circle, the next consideration for compatibility is the LENS MOUNT, or the physical connection of the lens to the camera. Most camera/lens manufacturers have their own type of mount. Some common ones include PL or Positive-Lock (ARRI), EF (CANON), F (Nikon), E (SONY), and Micro Four Thirds (used by PANASONIC, OLYMPUS, & BLACKMAGIC). That being said, no matter the manufacturer, all mounts fall into two main categories, PASSIVE or ELECTRONIC.
Passive Mounts are simply mechanical in nature. Electronic Mounts on the other hand involve passing information from the lens to the camera. This could simply mean passing along information or can be as complex as allowing control of the lens via the camera. (Resource: https://www.premiumbeat.com/blog/whats-the-difference-between-lens-mounts/)
ERGONOMICS
ERGONOMICS refers to the actual physical handling of a lens. The primary considerations are PRIME vs. ZOOM and CINE vs. STILL.
First consideration is PRIME vs ZOOM lenses. Prime lenses have fixed focal lengths, while zooms have the ability to alter their focal length. From a purely technical standpoint, compared one-to-one (same focal length, aperture, brand, etc), there should be no discernible difference between prime and zoom lenses. That being said, due to the more complex design of a zoom lenses (see image below), designers often have to make comprises that can impact performance. For example, prime lenses often are “faster”, or have the ability to have a wider aperture, and thus have the ability to have shallower Depth-of-Field. (Resource: https://www.bhphotovideo.com/explora/content/prime-vs-zoom-can-you-tell-difference).
The second consideration is CINE vs. STILL lenses. Due to the inherent differences between a Motion Picture (CINE) and photographic (STILL) environment, lenses have been designed for each. That does not mean lenses designed for one cannot be used for the other. Rather, it simply means that in order to fully utilize the design features of each, it is often best to use lenses for the work it is designed for.
For example, CINE lenses are primarily designed to have more finite control over lens parameters, such as aperture and focus, and thus have manual step-less or ‘de-clicked’ apertures and have long focus movement with very accurate focus marks (also referred to as ‘witness marks’). (Resource: https://thecinelens.com/2010/04/29/still-vs-cine-lenses/)
“If you’re doing a tracking shot, you can strengthen the composition throughout without it feeling like a zoom. It’s just more convenient to zoom in a bit and go again than to spend time changing the lens while everyone’s waiting. And if you’ve got to climb a hill, you’d rather take one zoom than a whole box of lenses.” — John Mathieson BSC (on use of zooms for Robin Hood)
TAKE-AWAY POINTS
Understanding the technical and creative impact of lenses will allow you to make the right choice for your individual taste and project!
In out next installment, we’ll discuss … Capturing the “Frame”!
Post No.17
A CINEMATOGRAPHER'S JOURNAL 
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