Video Camera Lens Fundamentals

Carlo Beltrano

www.canonbroadcast.com

LENS SELECTION CRITERIA

• What is the application? (studio, field, news, copy stand, etc.)

• Which camera model? (mount type, CCD size, 16:9/4:3)

• What VIEWING ANGLE is required? (wide, telephoto)

• How much of a ZOOM RATIO is required/desired?

• How will the lens be controlled? (manually, controls, remotely)

VIDEO LENS SPEC

20X8

FILM LENS SPEC

8~160mm

ANGLE OF VIEW

Determined by: Lens Focal Length & CCD size

Angle of View = 2tan-1 Image size (CCD or film)Focal Length X 2

Standard Image Sizes

2/3” CCD (4:3): 8.8mm X 6.6mm

2/3” CCD (16:9): 9.59mm X 5.39mm

1/2” CCD: 6.4mm X 4.8mm

35mm Movie: 24.92mm X 18.67mm

35mm Still: 36mm X 24mm

w

h

ANGLEHorizontal 1/2" Video (4:3 CCD) 2/3" Video (4:3 CCD) 2/3" HD Video (16:9) 35mm Still(in degrees)

[ccd width of 6.4mm] [ccd width of 8.8mm] [ccd width of 9.59mm] [gate width of 36mm]

82.2 3.7 5.0 5.5 20.6 77.3 4.0 5.5 6 22.5 63.2 5.2 7.2 7.8 29.3 61.9 5.3 7.3 8 30.0 51.2 6.7 9.2 10 37.5 43.6 8.0 11.0 12 45.0 35.5 10.0 13.8 15 56.3 29.8 12.0 16.5 18 67.6 27.0 13.3 18.4 20 75.1 22.6 16.0 22.0 24 90.1 21.7 16.7 22.9 25 93.8 18.2 20.0 27.5 30 112.6 15.6 23.4 32.1 35 131.4 13.7 26.7 36.7 40 150.2 12.2 30.0 41.3 45 168.9 11.0 33.4 45.9 50 187.7 10.0 36.7 50.5 55 206.5 9.1 40.0 55.1 60 225.2

FOCAL LENGTH

Focal Length and Image Size

VIDEO LENS NOMENCLATURE

J11aX4.5 BIRS J = 2/3” CCD IRS = w/ 2X

YH = 1/2” CCD VRS = w/ 0.8X WRS = w/ 2X & 0.8X KRS = none

B = compensated for prism

4.5 - 50 mm

9 - 100 mm (with 2X)

FNO =f

DThe smaller the FNO, the brighter the image

F-number vs T-number

FNO =

TNO =

TNO = 3

aperturefocal length

FNO

Transmitance %X 10

example

TNO =F2.8

86%X 10

2/3” LENS OUTPUT

11 mmDiameter

2/3” CCD (4:3 only)

2/3” CCD

(8.8 x 6.6 mm)

Lens image

11 mmDiameter

2/3” CCD vs 1/2” CCD

2/3” CCD (8.8 x 6.6 mm)Lens image

11 mmDiameter

1/2” CCD(6.4 x 4.8 mm)

2/3” CCD (16:9)

16:9 CCD

(9.59 x 5.39 mm)

Lens image

11 mmDiameter

2/3” 16:9 CCD (4:3 mode)

4:3 mode(7.19 x 5.39 mm)

Lens image

11 mmDiameter

Fixed 4:3 CCD

4:3 CCD (8.8 x 6.6 mm)

11 mmDiameter

Lens image

11 2 23

16:9 CCD

Switchable CCD in 16:9 Mode

16:9 mode

Lens image

11 mmDiameter

11 2 23

(9.59 x 5.39 mm)

1 1

4:3 mode

Lens image

11 mmDiameter

2 232 23

Switchable CCD in 4:3 Mode

(7.19mm x 5.39mm)

11

16:9 / 4:3 lens compensation

With 0.82X

Lens image reduced by 18.5%(9mm Diameter)

2 23 11 2 23

Lens image11 mm Diameter

11

Lens image reduced by approx. 20%

16:9 / 4:3 SWITCHABLE LENSES

J17aX7.7 WRS

J11aX4.5 WRS

J22aX7.6 WRS

16:9 / 4:3 SWITCHABLE LENSES(BOX TYPE)

• image size is 11mm diameter for both formats

HDTVlenses

vs.SDTV(NTSC)lenses

• Red and Blue abber. correction is better on HDTV lenses

• prism compensation is different between the two

• tracking error is minimized on HDTV lenses

• overall resolution is better on HDTV lenses

RGB OFFSET (2/3” LENSES)

10 um

5 um

NTSC

HDTV

When an SD lens is used on an HD camera, the MTF is greatly reduced when an image is slightly out of focus.

The amount by which an image is out of focus which causes only a 10% MTF loss in SDTV, causes a 50% MTF loss in HDTV.

MTF: HD vs SD

Depth of Field

Depth of field = x FNO x distance2

(focal length2) - (x FNO x distance)

permissible circle of confusion

Behind Object

for 2/3” ccd, =ccd diagonal

# of raster lines

for SDTV, = 0.021 mm

for HDTV, = 0.010 mm

for 16mm, ~ 0.009 - 0.012 mm

Range Calculator Test Q1

Find the focal length required to satisfy the following conditions:

• width of stage to be in the frame: 10ft

• distance between camera and stage: 70ft

• camera: 2/3” 4:3 ccd

Range Calculator Test Q2

How far back (distance) from a stage must a camera be placed in order to satisfy the following conditions:

• the full stage set height of 40ft must fill the frame (vertically),

• for maximum depth of field, the widest part of the lens is used: in this case an 8mm focal length,

• you are using a 2/3” 4:3 ccd camera.

Q & A