Tamron AF18 - Focal Lengths: Film vs. Digital; Angle of View Equivalents

Designed to capture the optimum scope when used
with a digital SLR camera
Designed to fit smaller-size image sensors
in order to reduce its diameter
Film and Digital
-- Angle of View and Focal Length
36mm
24mm
43.27mm
Film
35mm Film
about 23.2mm
about 15.5mm
27.9mm
Digital SLR with smaller-size imager
35mm Film
Principal
point
Principal
point
Angle of view
75˚ 23'
Angle of view
52˚ 58'
Lights
Camera
Focal
point
Focal
point
Film/
Image Sensor
Same
Focal Length
28mm
Mirror
Image
sensor
General
Image Sensor
Focal Length
General
Image sensor
*When pictures taken with a
Di-II lens mounted on a 35mm
film camera or digital SLRs
with image sensor larger than
24mm x 16mm, image corners
become dark
( ie., vignetting
becomes noticeable).
Film : 300mm
Digital : 200mm
Digital : 50mm
Film : 78mm
Digital : 18mm
Film : 28mm
*Film = 35mm format.
Imgaer taken with a digital
SLR with a smaller-size
imager are actually crop-
ped to about 70% scope.
*The general image sensors
(smaller-size imagers) are
about 24mm x 16mm.
However, the dimensions and
effective size differ depending
upon manufacturers.
A14QuickGuideRear
Image circle
for Di lenses
Vignetting when used
with a 35mm format camera
35mm Film
Diagonal
75˚33'
Horizontal
65˚36'
35mm
54mm
Equivalent
Diagonal
43˚28'
Horizontal
36˚40'
AF18-200mm
18mm
28mm
Equivalent
18mm
28mm
Equivalent
50mm
78mm
Equivalent
35mm
54mm
Equivalent
100 mm
155mm
Equivalent
200 mm
300mm
Equivalent
Diagonal
75˚33'
Horizontal
65˚36'
Diagonal
31˚11'
Horizontal
26˚7'
Diagonal
15˚53'
Horizontal
13˚14'
Diagonal
7˚59'
Horizontal
6˚38'
Diagonal
43˚28'
Horizontal
36˚40'
Angles of View
When designing a lens having a short focal length range (when designing a
wideangle lens), the diameter of the lens inevitably becomes large. However, in
designing the 18-200mm Di lens, Tamron has successfully solved this problem
by using an image circle designed to match that of general image sensor (smaller-
size image sensor), achieving almost the same compactness as the 28-300mm
lens (A061), which offers the same angles of view produced in 35mm film format.
36mm
24mm
about 23.2mm
about 15.5mm
Telephoto 7˚59'
Standard 31˚11'
Wide 75˚33'
*Digital = Digital cameras with smaller-size imagers.
50mm
78mm
Equivalent
Diagonal
31˚11'
Horizontal
26˚ 7'
100 mm
155mm
Equivalent
Diagonal
15˚53'
Horizontal
13˚14'
200 mm
300mm
Equivalent
Diagonal
7˚ 59'
Horizontal
6˚38'
AF18-200mm
Model A14
Since the sizes of 35mm film format are different from
the image sensor of a digital camera, the scope of the
image captured is different even when focal lengths
are the same (i.e., angles of view differ).
The 18-200mm Di is designed to capture optium
scope when used with a general digital SLR, espe-
cially at its wide angle side.
Tamron 18-200mm Di
-
Different angles of view
-
new