Sony ALC-F62Z Specification Guide

  

The job of varying focal length in a zoom lens 
requires a fairly complex mechanism that 
translates zoom ring rotation into precise group 
movement along the optical axis of the lens. Zoom 
mechanisms must be precisely manufactured 
to exacting tolerances so that all elements and 
groups stay in perfect alignment throughout the 
zoom range.

Focusing is sometimes accomplished by moving 
the entire lens closer to or further away from 
the image sensor plane, although some lenses 
employ a “floating construction” in which groups 
of elements move independently in order to 
maintain optimum optical performance at all 
shooting distances.

There is a lot of pertinent information 
printed or engraved on the outside of 
lenses that can help you understand their 
characteristics and how to best use them.

Here are a few examples.

Read your lenses

A look inside

Lenses: How they capture and control light

The linguistic roots of the word “photography” are the Greek words meaning “light” and “drawing.” Photography is “drawing 
with light,” and lenses are the brushes. After their imagination, lenses are the photographer’s primary creative tools. The way 
a lens captures and presents an image to the camera’s sensor determines the visual outcome more than any other factor. 
The ability to choose the right lens and use it well is one of the most important skills an aspiring photographer should acquire. 
In this brief guide we’ll look at some of the basics that will help you to choose lenses that are suited to your needs, and 
make the most out of them to create truly satisfying photographs.

Our eyes do it, cameras do it, even a simple 
light-tight box with a tiny hole in one end will 
do it: the feat of turning light into an image 
can only be accomplished by first capturing 
the light from a scene and projecting it onto 
a surface. That surface, the “image plane,” 
can be a wall, a piece of film, a sensor, or 
the retina in our eye. In all cases the image 
is projected upside-down and horizontally 
reversed. Let’s take a look at the precursor of 
modern cameras, the simplest camera of all: 

the pinhole camera. In a pinhole camera a tiny 
hole is all that’s needed to project an image.

To make this easier to understand, remember 
that light normally travels in straight lines, then try 
to imagine the subject being photographed as 
being made up of a multitude of points of light of 
appropriate brightness and color.

In the example in Figure 1, light from a point at 
 the top of the tree travels in a straight line 

through the pinhole and reaches a point at 
the bottom of the image plane, whereas light 
from a point at the bottom of the tree ends up 
at the top of the image plane after passing 
through the pinhole.

The real-world scene becomes an image 
projected on the image plane, upside-down 
and reversed left-to-right. 

Pinholes can “project” images, but they are limited and inflexible. In 
order for the projected image to be sufficiently sharp, the hole must be 
very small, but this also means that the projected image is very dim. 
In principle, lenses work similarly to the pinhole, but they are capable 
of capturing more light from each point on the subject, and therefore 
project a much brighter image. A lens can also bring more light into 
sharp focus. That’s helpful because it means we can use short sub-

second exposures rather than having to make sure that both the  
camera and subject stay perfectly still for many minutes or even hours, 
which is usually the case with a pinhole camera. Other advantages are 
that lenses can be made in a variety of focal lengths from wide-angle to 
capture expansive scenes or telephoto to photograph distant subjects.
Modern lenses are precision optical devices that give photographers 
boundless freedom to realize their creative vision by “drawing with light.”

A pinhole camera is basically a light-tight box 
with a small hole in one end

Figure 1. A simple pinhole of appropriate size 
is capable of projecting a sharp but dim image

Figure 2. A lens uses the principle of “refraction” 
to gather more light from the subject and project 
a sharp, bright image

Projecting an image

Refraction: bending light

The physical principle that allows lenses to 
gather and focus light is called “refraction.” 
Refraction causes lightwaves to change speed 
and direction when they pass from one medium 

(air, for example) to another (glass, for example), 
and allows lenses to be designed to “bend” light 
in a controlled way. The “refractive index” of an 
optically transparent medium is a measure of 
the speed of light in that medium, and therefore 
the degree to which light will be “bent” by that 
medium. Optical materials that have different 
refractive indices—conventional optical glass and 
ED glass, for example—are sometimes combined 
in lenses to achieve the desired characteristics.

This is the most basic, most important 
characteristic of any lens. Focal length plays 
a primary role in determining what types of 
subjects and compositions the lens is suitable  
for (see page 10 for more details).

Lenses marked “SAM” or ”SSM” feature 
built-in motors that drive the lens’s 
focusing mechanism. Lenses that 
don’t have internal motors are driven 
by a motor in the camera body  

(see page 17 for more details).

This number represents the maximum 
aperture, or “f-number,” of the lens 
and tells you how “bright” the lens is 

(see page 9 for more details).

Sony lenses marked “DT” (Digital 
Technology) have been specifically 
designed for use on APS-C format 
A-mount cameras (see page 8 for 
more details). 

This switch lets you switch between 
autofocus and manual focus modes. 

Focal length

Distance scale

Autofocus drive type

Maximum aperture

Lens format

AF/MF switch

Lens element

Lens group

Mount

Aperture

Lens barrel

Wide

Medium

Telephoto

Aspherical lens  (see page 16 for more details)
ED glass  (see page 16 for more details)

Light reflected by the subject is effectively collected 
and focused by the lens elements to project an 
image on the camera’s image sensor plane.

Subject

Light

Lens element

Focal point

Viewfinder

Mirror

Pentaprism (flips the image so it can viewed in proper orientation)

Image 
sensor plane

Focal length

Optical axis

All modern photographic lenses are “compound” 
lenses that use a number of lens “elements” 
precisely mounted along the same optical axis. 
The use of multiple elements allows lens designers 
to effectively reduce optical aberrations so you 
get nice sharp, clean images.

“Elements” are the individual pieces of specially 
shaped glass that make up the lens. A “group” 
consists of two or three elements that have been 
glued together to function as a unit. Sometimes 
groups consist of different types of glass that 
have been combined in order to control some 
form of aberration. Lenses are sometimes 
described in terms of the number of elements 
and groups they contain. You’ll hear terms such 
as “7-group 9-element lens.” 

Fixed focal length lenses, also known as “prime” 
lenses, generally have the simplest construction 
with the fewest groups and elements. Zoom 
lenses require a larger number of groups/
elements to support the zoom functionality.

While most lens elements are “spherical,” 
meaning that one or more surfaces form part 
of a sphere, some lenses include “aspherical” 
elements. Aspherical elements have more 
complex shapes than simple spherical elements, 
and are much more difficult and more expensive 
to produce. Aspherical elements are sometimes 
used in wide-angle and fast standard lenses, 
where they can be effective in reducing certain 
types of aberration. 

TECH TALK

The distance scale indicates the 
approximate distance from the 
camera’s image plane to the object 
that the camera is focused on.

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