Transcript Document

Production Technologies
The Central Role of the Lens
in
HDTV Imaging
Laurence J. Thorpe
Broadcast & Communications
Canon U.S.A.
Broadcast Transmission Systems
> Signal
Integrity
> Quality
of Service
> Channel capacity
> Transmission
Impairments
> Noise
> Interference
> Fading
> Ghosts
> Reflections
> Bit
Error Rates
The HDTV Lens as Transmission System
>
Optical Image Integrity
>
>
>
Quality of Service – namely, Quality of Image
“Channel” capacity – namely, Sensitivity
Transmission Impairments
>
>
>
>
>
Fundamental Optical Limitations
Distortions
Aberrations
Ghosts
Reflections
HDTV Lens as Transmission System
HDTV Production
Creative Role
of the
HD Lens
Role of the HDTV Lens
Lighting
Scene
Lens
Digital Camera
Represent
Capture
In digital domain
on Digital Media
Digital Recorder
Create
The
Optical Image
Image
is completely defined
at this point
Creation of the Optical Image
Multidimensional Aspect of the Optical Image
Shaping the Image
>
Angle of View
>
>
Zoom
>
>
Real-time dynamic adjustment to Angle of View
Depth of Field
>
>
Framing of a chosen image segment from object scene
Expressing a 3-D representation on a 2-D image
Perspective
>
Further creative adjustment to sense of picture depth
Creation of Optical Image
Multidimensional Aspect of the Optical Image
Qualifying the Picture
>
Contrast
>
>
Color Reproduction
>
>
Tonal Reproduction
Lens Transmittance Characteristic
Picture Sharpness
>
Resolution – what is this in the context of “distant” viewing ?
Quality Optics for HDTV
The
Lens-Camera
Imaging System
Role of the Digital Camera
Optical Representation
Of the
Object Scene
Digital Modification
Opto-Digital
Transformation
Imaging
System
Digital Representation
Of the
Optical Image
RGB Digital Processing
RGB
Digital
Facilitates adjustments
to meet the prescribed
HDTV Production Standard
Digital
Representation
According to
ITU 709
Detent Settings:
• ITU 709 High Def Standard
Role of the Digital Camera
Optical Representation
Of the
Object Scene
Digital Modification
RGB Digital Processing
Opto-Digital
Transformation
Imaging
System
Facilitates adjustments to:
RGB
Digital
• Tonal Reproduction
(Gamma and Knee)
• Color Reproduction
(Colorimetry)
• Picture Sharpness
(Image Enhancement)
Digital Representation
Of the
Optical Image
Adjustable Settings:
• Creative Control
Digital
Representation
According to
Creative
&
Aesthetic
Desires
The Science of Optical Design
>
Is a Science of Optimization
>
Dealing with Multiple Variables
>
>
>
Multiple Picture Attributes
Multiple Aberrations
These Parameters are Dynamic – in that they vary with:
>
>
>
Zoom
Focus
Iris
HDTV Studio Zoom Lens
HDTV Studio Zoom Lens
Variator
Compensator
HDTV Zoom Lens
Wide Angle
Mid Zoom Range
Telephoto
The Science of Optical Design
Multiple Attributes
Contributing to
Overall
Image Performance
Image Performance Parameters
> Sensitivity
> The inherent Optical Speed of the lens (the “channel” capacity)
> Picture Contrast
> Tonal Reproduction (integrity of the grey scale)
> Reproduction of Dark portions of the scene
> Handling of strong light sources
> Color Reproduction
> Color Gamut
> Picture Sharpness
> Horizontal and Vertical Resolution
> Limiting Resolution
> Resolving Power
The Science of Optical Design
Multiple Impairments
Attempting to Detract
from Overall
Image Performance
Lens Aberrations
For a single Lens Element:
• There are FIVE aberrations
for monochromatic light
• Mathematically predicted by
a German scientist Seidel
in 1856
Five Aberrations of Seidel
1. Spherical Aberration
> Parallel light at lens edge converges to focal point nearer to lens
than light passing through center
2. Coma
> Comatic aberration is a phenomena visible in the periphery
of an image – light rays entering the edge of the lens at an angle
converge in the form of a comet
3. Astigmatism
> Off-axis subject point appears as an ellipse
4. Curvature of Field
> Focusing on a flat object field produces a bowl-shaped optical image
5. Distortion
> Geometric distortions – of the pincushion and barrel form
Optical Limitations & Aberrations
>
Optical Physical Limitations
>
>
>
>
Diffraction – imposes a fundamental limitation to MTF
Relative Light Distribution – Light fall-off from picture center
Focus Breathing – Angle of view changes with focus control
Distortions & Aberrations
>
>
>
>
Spherical
Curvature of Field
Coma
Astigmatism
>
Geometric
>
Chromatic Aberrations
>
>
Flare, Ghosting, and Veiling Glare
Unwanted stray rays – stimulated by highlights
}
Focusing Distortions
(Lateral and Longitudinal)
Quality Optics – Optimizing Multiple Variables
Perfect
Lens
Total Lens
Performance
• Maximum Attributes
• Minimum Impairments
Increasing Costs
SDTV
Lens
HDTV
Lens
• Collective Technology Refinements
• Collective Manufacturing Processes
HDTV Lens-Camera Resolution
Concept
Of
Modulation Transfer Function
(MTF)
Modulation Transfer Function (MTF)
• The Contrast of these Spatial Frequencies
• Diminishes as the frequency increases
• The Behavior of that Contrast with Frequency
• Described by the Modulation Transfer Function
Image Resolution
as Described by MTF Characteristic
100 %
MTF
Lens
Contrast
Modulation Transfer Function
(MTF)
Lens
Resolving Power
Video
Optical
Limiting
Resolution
TVL / ph
LP / mm
Concatenation of MTF
(Provides System MTF)
Camera
Sampling
Lens
MTF #1
X
MTF #2
Human
Visual
System
Display
X
MTF #3
X
MTF #4
Typical 1920 (H) x 1080(V) HD Camera and Lens
SMPTE Specified Filter
872 TVL/ph
30 MHz
Carrier
100%
Lens
Horiz
MTF
50%
45%
HD Camera
800
Ref
Measurement
1080
Nyquist Limit
Horizontal
2160
TVL/ph
HDTV Resolution
Picture
Sharpness
Picture Sharpness
Visual Picture Sharpness
Is
Proportional to the
Square of the Area under the MTF Curve
Otto Schade Snr
RCA Research Labs
Picture Sharpness
100 %
Contrast
Level
MTF
2
Modulation Transfer Function
(MTF)
Limiting
Resolution
Spatial Frequency
Video TVL / ph
Optical LP / mm
Image Resolution
100 %
Most important region of the MTF curve
Contrast
Level
Picture
Sharpness
Least important
region
Image
Texture
Picture Definition
Resolving
Power
TVL/ph
Line Pairs/mm
The Importance of In-Band MTF
872 TVL/ph
100%
30 MHz
Carrier
Lens-Camera
Typical Spec
Horiz 50%
MTF
200
400
600
800
Ref
Measurement
1080
Nyquist Limit
Horizontal
2160
TVL/ph
The Importance of In-Band MTF
872 TVL/ph
100%
30 MHz
Carrier
Lens-Camera
Typical Spec
Horiz 50%
MTF
Unspecified – but
Vitally important
To Picture Sharpness
200
400
600
800
Ref
Measurement
1080
Nyquist Limit
Horizontal
1920
TVL/ph
Fs
The Studio Lens
Optimization of Picture Sharpness
High MTF
Across
Image Plane
• High
Contrast
• Flat
Relative
Illumination
• Minimum
Defocusing
Distortions
Relative MTF of HDTV and SDTV 2/3-Inch Studio Lens
Measured at Picture Center
Wide-angle @ F-4.0
16:9 5.5 MHz SDTV
Band-edge
100
SDTV
MTF
%
20
40
60
80
LP/mm
Line-Pairs per Millimeter
Relative MTF of HDTV and SDTV 2/3-Inch Studio Lens
Measured at Picture Center
Wide-angle @ F-4.0
16:9 5.5 MHz SDTV
Band-edge
100
Bandpass
Of
Interest
SDTV
MTF
%
20
40
60
80
LP/mm
Line-Pairs per Millimeter
MTF of 2/3-Inch HDTV Studio Lens
Measured at Picture Center
Wide-angle @ F-4.0
100
HDTV
MTF
%
20
40
60
80
LP/mm
MTF of 2/3-Inch HDTV Studio Lens
Measured at Picture Center
Wide-angle @ F-4.0
1080/60i HDTV
Band-edge
100
HDTV
MTF
%
20
40
60
80
LP/mm
Relative MTF of HDTV and SDTV 2/3-Inch Studio Lens
Measured at Picture Center
Wide-angle @ F-4.0
16:9 5.5 MHz SDTV
Band-edge
1080/60i HDTV
Band-edge
100
HDTV
Bandpass
Of
Interest
Bandpass
Of
Interest
MTF
%
20
40
X 2.7
SDTV
60
80
LP/mm
Line-Pairs per Millimeter
MTF of 2/3-Inch HDTV Studio Lens
Measured at Picture Center
Wide-angle @ F-4.0
Optical
Reference
100
Camera
1080/60i HDTV
Reference Band-edge
HDTV
MTF
%
20
40
56
60
LP/mm
74
LP/mm
80
LP/mm
MTF of 2/3-Inch HDTV Studio Lens
Measured at Picture Center
Wide-angle @ F-4.0
Optical
720P Reference
Camera
720/60P HDTV
Reference
Band-edge
100
HDTV
MTF
%
20
40
56 60
LP/mm
LP/mm
49
80
LP/mm
Relative MTF of HDTV and SDTV 2/3-Inch Studio Lens
Measured at Picture Center
16:9 5.5 MHz SDTV
Band-edge
100
Wide-angle @ F-4.0
Optical
Reference
1080/60i HDTV
Band-edge
HDTV
SDTV
MTF
%
20
40
56 60
80
LP/mm
Line-Pairs per Millimeter
Picture Sharpness and MTF
MTF is Dynamic
Across the
Image Plane
16:9 HD Lens MTF Measurements
7.0 mm
5.4 mm
Corner
Middle
3.9 mm
9.6 mm
Center
3.5 mm
2.0 mm
Lens MTF across Image Plane
(Measured at 56 Lp/mm or 600 TVL/ph @ f-4.0)
100
90
80
70
MTF
%
Center
Middle
Corner
Lens MTF across Image Plane
Measured at 56 Lp/mm (or 600 TVL/ph) @ F-4.0
100
90
HDTV
80
70
SDTV
MTF
%
Center
Middle
Corner
Picture Sharpness and MTF
MTF
Varies with
Focal Length
Variation of MTF with Zoom
100
Measured at Picture Center 56 Lp/mm @ F-4.0
90
HDTV
80
70
MTF
%
SDTV
Focal Length in mm
Wide
15
30
45
60
90
120
Tele
MTF Profile with Focal Length
(Measured at 56 Lp/mm)
100
90
Mid-range
80
Telephoto
70
Wide-angle
MTF
%
Center
Middle
Corner
Picture Sharpness and MTF
MTF
Varies with
Object Distance
Variation of MTF with Object Distance
Measured
at
Picture
Center
at
56
Lp/mm
@
F-4.0
100
HDTV
90
80
70
MTF
%
SDTV
Object Distance in Meters
0.6
1.0
2.0
3.0
5.0
10.0
50.0
Infinity
Picture Sharpness and MTF
MTF
Is Dynamic
With
Aperture Setting
MTF as a Function of Aperture
The Perfect Lens (Diffraction Limited)
HDTV Passband
Optical
Reference
100%
30MHz
872 TVL/ph
HD Reference
27.5MHz
800 TVL/ph
F 2.0
F 4.0
Modulation
Transfer
Function
(MTF)
F 8.0
SDTV
400 TVL/ph
F 16.0
20
40
30 Lp/mm
(1080-Line System)
60
80
56 Lp/mm
74 Lp/mm
600 TVL/ph
800TVL/ph
Lp/mm
TVL/ph
MTF Profile with Focal Length
(Measured at 56 Lp/mm)
100
90
80
70
Telephoto
Mid-range
Iris
Wide
Open
Wide-angle
MTF
%
Center
Middle
Corner
MTF Profile with Focal Length
(Measured at 56 Lp/mm)
100
90
Mid-range
80
Aperture
F- 4.0
Telephoto
70
Wide-angle
MTF
%
Center
Middle
Corner
HDTV Lens
Light Management
Within the
Lens Transmission System
Light Management
1. Spectral
>
>
Transmittance
Sensitivity
Color Reproduction
2. Relative
Light Distribution
3. Chromatic
>
>
Aberrations
Lateral
Longitudinal
HDTV Lens
Spectral
Transmission
Lens Spectral Transmittance
Lens Spectral Transmittance
Spectral Transmittance
Lens
Color Reproduction
HDTV Color Reproduction
CCD
Imager
Beam
Splitter
Lens
Lens
Spectral
Transmittance
Sample
&
Hold
Amplifier
X
Prism
Spectral
Shaping
A/D
X
Imager
Spectral
Response
X
Digital
Processing
Linear Matrix
IRcu t Filter(CM 500S)分光特性
IR Cut Filter
1. 0
1. 0
0. 8
0. 8
In ten sity
In ten sity
Studio 光源分光特性（
Tungsten 3200
3200K ）degree
0. 6
0. 4
0. 2
0. 0
400
0. 6
0. 4
0. 2
450
500
550
600
650
0. 0
400
700
450
500
W a ve (n m )
1. 0
550
600
650
700
650
700
W a ve(n m )
Generic
Camera
Prism
Prizm (H D-SON
Y)分光特性
CCD Imager
CCD分光特性（ SO N Y）
1. 0
0. 8
0. 6
Intensity
In ten sity
0. 8
0. 4
Bch
G ch
Rch
0. 2
0. 6
0. 4
0. 2
0. 0
400
450
500
550
W a v e(n m )
600
650
700
0. 0
400
450
500
550
W a v e (n m )
600
Many Variables relating to Color Reproduction
CAMERA
PRISM
Canon
Hitachi
Ikegami
Panasonic
Sony
Thomson
Fujinon
IMAGER
Matsushita Sony
Toshiba Angenieux
LENS
Canon Fujinon
Testing the HDTV Lens
Relative Light Distribution
Specification of Light Distribution
Image Height
5.4 mm
2.7mm
5.5mm
4.8mm
9.6 mm
Lens Relative Light Distribution
>
The Lens F-Number
>
1.
Natural Vignetting
>
>
2.
Off-axis Points do not receive this same Amount of Light
Cosine 4th Power Law – light reaching the image margins decreases
as the 4th power of the Cosine of angle of view
Optical Vignetting
>
3.
Indicates the Amount of Light collected at the Center of the Image
Oblique light rays are presented with a lesser lens opening than on-axis rays
Mechanical or “Hard” Vignetting
>
Caused by extensions added to the lens – lens hoods, matte box holders etc
Lens Light Distribution
Lens Light Distribution