class=MsoNormal align=center style='margin-bottom:0cm;margin-bottom:.0001pt;
text-align:center;mso-line-height-alt:0pt'>style='font-size:14.0pt;font-family:Arial;mso-bidi-font-family:Arial'>Double
Vision: Cine Lens Quality
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;mso-line-height-alt:
0pt'>style='font-size:14.0pt;font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;mso-line-height-alt:
0pt'>style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>Author:
Ian Marshall
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;mso-line-height-alt:
0pt'>style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>Principal
Optical Development Engineer
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;mso-line-height-alt:
0pt'>style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>BAE
Systems
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;mso-line-height-alt:
0pt'>style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>Rochester
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;mso-line-height-alt:
0pt'>style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>Kent
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;mso-line-height-alt:
0pt'>style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>UK
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;mso-line-height-alt:
0pt'>style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>ian.marshall@baesystems.com
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;mso-line-height-alt:
0pt'>style='font-size:14.0pt;font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;mso-line-height-alt:
0pt'>style='font-size:14.0pt;
font-family:Arial;mso-bidi-font-family:Arial'>Abstract
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;tab-stops:
list 72.0pt 108.0pt'>style='font-size:12.0pt;line-height:115%;font-family:
Arial;mso-bidi-font-family:Arial'>Cine lenses are used to produce movies, TV
productions and adverts. Producers are trying to emotionally engage viewers
with the content, whereas the imaging quality of the lens obstructs or enhances
this engagement. In particular, the aesthetics of a lens are not fully
understood from a scientific standpoint. There is Ôdouble visionÕ: the users want
more than lens designers fully understand. This paper takes data from two
lenses tests conducted by users and a sample still image taken from the web to
illustrate some of the underlying lens design theory.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;mso-line-height-alt:
0pt'>style='font-size:14.0pt;font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;mso-line-height-alt:
0pt'>style='font-size:14.0pt;
font-family:Arial;mso-bidi-font-family:Arial'>About the Author
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>To introduce myself, I am currently working
in aerospace and defence, but have worked as a lens designer for Cooke Optics
designing 5/is and miniS4s. I am basing this presentation on that experience
and subsequent viewing of sample videos from the web.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:14.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:14.0pt;font-family:Arial;mso-bidi-font-family:Arial'>Introduction
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>This paper is based on the following premise:
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Cine lenses are used on movies, TV
productions and adverts where the cinematographer is attempting various forms
of emotional engagement of the viewers.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The lens and camera system, including post
processing and projection, creates a ÔportholeÕ through which the viewer engages
with the artistic composition.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The imaging quality of the lens obstructs or
enhances this engagement. Small variations in lens characteristics (including
aberrations) are therefore important to end users.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>An example of a quote taken from the web is ÒI
have had discussions with rental companies about lenses looking better than
other lenses with greater MTFÓ.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>This paper takes data from two lenses tests
conducted by users and a sample still image taken from the web to illustrate
some of the lens design theory affecting the tests.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>I propose that there is Ôdouble visionÕ: the
users want more than lens designers fully understand.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The characteristics that the users want are
usually compromised or traded off in a conventional lens design. Furthermore, some
important characteristics are not understood from a scientific standpoint
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify'>style='font-size:12.0pt;line-height:115%;font-family:Arial;
mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify'>style='font-size:12.0pt;line-height:115%;font-family:Arial;
mso-bidi-font-family:Arial'>To illustrate the way lenses might be used on a
set, I have copied a clip from the ÔThe Big Ole Lens Test PartyÕ with permission
from Ben Eckstein et al.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify'>style='font-size:12.0pt;line-height:115%;font-family:Arial;mso-bidi-font-family:
Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>In this view the camera is in a single position
to capture images through different lenses on the same focus settings; so as to
look for different properties in the lenses. By keeping all else the same, the
differences between the lenses are exposed.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>On a real set, there will usually be more
than one camera fitted with different focal length lenses set to different
focus distances. Because the images produced by different lenses have to have
closely matching aesthetics (else the viewer is distracted by the lens
differences); the imaging characteristics of different lenses in a set working
at different settings must also be closely matched.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The actors repeat short scenes many times,
and the images from different perspectives are carefully edited to avoid
mismatch.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:14.0pt;font-family:Arial;mso-bidi-font-family:Arial'>Focusing
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The first issue that I am presenting is focusing.
The focus puller controls the lens focus to match the actorÕs positions using a
variety of methods, which require the focus marks on the lens to be accurate.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The clip shows how the story line is
controlled by accurate focusing which controls the centre of attention. The
focusing is on the actors faces, it follows the storyline, and is accurate and
smooth.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Notice also how the centre of attention, and
hence the sweet spot required of the aberration compensation, may be quite a
long way off centre.
class=MsoNormal style='text-align:justify'>style='font-size:12.0pt;
line-height:115%;font-family:Arial;mso-bidi-font-family:Arial'>(please double
click the separate video clip ÔZeissCP2-windows.wmvÕ)
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Because the focus puller controls lens focus
to actorÕs positions, the focus puller does not want the focus distance to vary
with aberrations on stopping down. He uses a variety of methods and needs the
focus marks on the lens to be accurate. Some methods use the lens focus marks
as a ÔrulerÕ.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Also, the through focus Ôroll offÕ needs to be
consistent from view to view and lens to lens. This refers to the aesthetic of
how the image blurs and changes colour (due to secondary spectrum) as the
object changes distance to the lens.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Therefore aberrations affecting focus roll
off should be consistent across the prime lens set. And lens aperture settings
that vary between views of the same scene must not change the look. Hence variations
in aberration form with aperture should be controlled.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The need to match these aberration properties
between different focal length lenses in a set is a demanding task. And some
users stop lenses down two stops from full aperture as a rule of thumb to
reduce variations.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>To illustrate the scale of when an aberration
type is too large to be acceptable, I have generated a simple lens design with higher
order Spherical Aberrations. The transverse aberration curves show about
0.035mm of spherical aberration at full aperture (corresponding to T/1.4). At
T/2 the aberration form is mostly vignetted.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>
style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>A simple calculation of monochromatic MTF
through focus shows the variation of peak MTF at different positions at the
sensor plane.
class=MsoNormal>style='font-size:12.0pt;line-height:115%;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal>style='font-size:12.0pt;line-height:115%;font-family:
Arial;mso-bidi-font-family:Arial'>The longitudinal difference of 0.017mm is a
variation that some users have stated to be a problem in lens blogs. As a general
rule, I have noticed that lenses without full fiducial markings on the focus
ring suffer from this variation. Therefore I suggest users should beware lenses
without such marks.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>lang=EN-US style='font-size:12.0pt;
font-family:Arial;mso-bidi-font-family:Arial;mso-ansi-language:EN-US;
mso-no-proof:yes'>style='font-size:12.0pt;
font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal>style='font-size:14.0pt;line-height:115%;font-family:Arial;mso-bidi-font-family:
Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify'>style='font-size:14.0pt;
line-height:115%;font-family:Arial;mso-bidi-font-family:Arial'>Bokeh
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The second issue I am presenting is the well-known
out of focus effect calledstyle="mso-spacerun:yes"> ÔBokehÕ.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Taking the previous demonstration lens
design, one can trace rays through the sensor plane to simulate the effects of
going out of focus. As shown in the ray trace diagram, the lens aberrations
cause hard or soft edges to out of focus highlights, depending on which side of
focus the highlight is. In this diagram, the small ray patterns might represent
the focus roll off characteristics of the highlight. The larger patterns which
are further away from focus represent the ÔBokehÕ characteristic. So Bokeh and
focus roll off are linked issues. Notice how a medium sized aberration, in this
case +/-0.035mm, has a large effect on through focus aesthetics. Hence is one
reason why this author believes MTF to be a poor measure of image quality.
class=MsoNormal>style='font-size:
12.0pt;line-height:115%;font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal>style='font-size:12.0pt;line-height:115%;font-family:
Arial;mso-bidi-font-family:Arial'>The basic cause is Schlieren photography. A
small highlight acts as a point source. Ray tracing through a lens causes light
to either concentrate or be dispersed at the sensor image plane. The effect
reverses on the opposite side of focus; which is a key indicator of a phase
effect in the lens. The highlight intensity is proportional to ray density,
which is proportional to wave-front curvature. I have seen curvatures lower
than 0.1 microns have a strong effect in test images.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal>style='font-size:12.0pt;line-height:115%;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>In the example shown below, taken from the
web under open permissions from Ashley Pomeroy, the lights simulate Schlieren
photography with hard edges due to lens aberrations.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:
12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>By normal optical theory, the hard edged ring
is convolved with image information to create artefacts in the background.
Hence, every time there is a transition from light to dark in the background,
the feature has a hard edge. For example, the stair cases. Sometimes
cinematographers like this and sometimes they do not.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>But quality lens sets need the same Bokeh and
focus roll off for every lens in the set so that images taken from different
angles by different lenses can be matched. Therefore the higher order aberrations
must match across a range of focal lengths.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>This requires a tighter aberration compensation
than is offered only by a good MTF. Notice again from the sample image how the
higher order aberrations at the edge of the field of view may be important.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>From an optical engineering point of view, Bokeh
acts like a built in interferometer in every lens. To use it, it is necessary
to image an out of focus point highlight, like an LED Christmas tree light. The
result is a very sensitive ÔinterferogramÕ that measures less than 0.5 microns
wave-front error. Though to get a quantitative measure requires a lot of
interpretation, as the Bokeh is measuring localised wave-front curvature. One
key indicator that one is looking at aberrations rather than some other effects
occurs because the phase errors in the lens reverse the distribution in
intensity across the Bokeh on the opposite side of focus.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>A lot of lenses have zonal aberrations that
induce noticeable hard out of focus edges in the distant background. However,
the aberrations are also changing the ÔsmoothnessÕ of the gradual softening of
an image as the lens goes out of focus. The best lenses have smooth focus roll
off with small amounts of zonal aberrations.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>And the zonal aberrations are matched to give
a consistent focus roll off over the whole range of lenses, which demands a
higher quality standard than just achieving a reasonable MTF.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:14.0pt;font-family:Arial;mso-bidi-font-family:Arial'>Colour
Matching
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The third issue I am discussing is colour
matching.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Aberrations affect how colours are reproduced.
Not just in obvious ways. Colour balancing requires the red, green and blue
signals from the sensor to be matched in a consistent way. For example, if the
green signal is softened through aberrations in comparison to the red and blue
signals, then the lens will present a false colour balance to the sensor. The
differences should be matched across a complete set of prime lenses so that the
images look the same.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Different lens types have different
reputations. For example blog comments on Zeiss lenses include the comments
ÔflatterÕand Ôhigher white contrastÕ.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Cooke lenses are called ÔrounderÕ with a
greater colour depth.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal>style='font-size:12.0pt;line-height:115%;font-family:
Arial;mso-bidi-font-family:Arial'>An extreme test of colour matching is to
image reflections from scrunched up foil, as with this example from the SALT
III lens tests. These images are from the two most consistent lens sets in the
tests. Both look similar at T/2.8, though with a slight colour difference.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:
12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>However, at T/1.4 there is
a substantial difference between the lenses. But there is an even greater
difference between images produced by the same lens at different apertures. In
both cases, one would assume that images captured by the same lens at different
apertures would require post processing to colour match. The variations between
aperture settings indicate strongly that the difference is due to lens
aberrations.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The images are courtesy of Matt Hayslett et
al.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-top:0cm;margin-right:0cm;margin-bottom:0cm;
margin-left:36.0pt;margin-bottom:.0001pt;text-align:justify;mso-line-height-alt:
0pt'>style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The effects of colour matching are most
obvious when the images are shown side by side.
class=MsoNormal>style='font-size:12.0pt;line-height:115%;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>LetÕs return to the Big OLE lens test party
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>(please double click on the separate video
clip ÔSidebySide-windows.wmvÕ)
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>If one views the blog, then the comments by
the lens testers show that they recognised a difference between these images.
This is despite the scenes being shot at T/4. Assuming the differences are due
to aberrations, then the aberrations are small, but still produce a visible
effect.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>This implies that intercut lenses must be
aberration balanced to very fine consistency, and that MTF is not accurate
enough to define the quality standard.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The owners of the video clip are identified
from the credits.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Two still images where captured for further analysis.
A line of pixel values was taken across similar parts of each image, shown by
the yellow lines. The lenses were the Cooke 35mm and the Zeiss Superspeed 35mm.
One would expect that the effects of aberrations in the lenses are well
softened and suppressed by the T/4 aperture and the low video quality
reproduced by the web.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>lang=EN-US style='font-size:12.0pt;
font-family:Arial;mso-bidi-font-family:Arial;mso-ansi-language:EN-US;
mso-no-proof:yes'>
style='font-size:12.0pt;
font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='text-align:justify'>style='font-size:12.0pt;
line-height:115%;font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Various factors could also affect RGB signal
levels. For example, differences in brightness and contrast caused by
differences in the angle of the face to the lighting and differences in the
actorÕs position relative to his ÔmarksÕ. And one would expect spectral
transmission differences between the lenses to change the relative levels of
the RGB channels. One way of attempting to find a pattern, despite these
variations, style="mso-spacerun:yes"> is to look at the
differences between adjacent pixel values across the lines, as shown.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>
style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>There are
differences between the lenses, but no obvious relationship to lens aberrations.
Isolating patterns that are only due to colour matching aberrations requires
further processing.
class=MsoNormal style='text-align:justify'>style='font-size:12.0pt;
line-height:115%;font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>I have therefore used simple mathematics in
an analogous way to CIE chromaticity coordinates. At each pixel, an approximate
equivalent to CIE colour coordinates is calculated, by taking one signal and
dividing it by the sum of all three signals. The pixel to pixel differences of
these coordinates is calculated.
class=MsoNormal>style='font-size:12.0pt;line-height:115%;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal>style='font-size:12.0pt;line-height:115%;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal>style='font-size:12.0pt;line-height:115%;font-family:
Arial;mso-bidi-font-family:Arial'>By plotting out the blue and red constructs
relative to the green construct, one can see a more pronounced relationship of
the colour coordinate variations in the Cooke lens. One could intuitively
relate this to the aberrations in the lens designs.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>lang=EN-US style='font-size:12.0pt;
font-family:Arial;mso-bidi-font-family:Arial;mso-ansi-language:EN-US;
mso-no-proof:yes'>
style='font-size:12.0pt;
font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Because the analysis indicates that there is
a better correlation between red and green and blue and green pixel values when
imaged with the S4 lenses, and because the lens testers are commenting on the
better skin rendition of the Cooke lenses, I hypothesise that a better
rendition of skin tones is caused by the red and blue contrast changes more
faithfully following the green contrast changes. And that this is caused by the
matching of red green and deep blue aberrations in the lens design.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>In theoretical analysis, I am using public
domain information of the RGB absorption spectra of typical Kodak film. The absorption
peaks correspond approximately to Ceg wavelengths, which are:
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>e: 546nmstyle='mso-tab-count:1'> g:
436nmstyle='mso-tab-count:1'> C:
656nm
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal>style='font-size:12.0pt;line-height:115%;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-top:0cm;margin-right:0cm;margin-bottom:0cm;
margin-left:36.0pt;margin-bottom:.0001pt;text-align:justify;text-indent:-36.0pt;
mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:Arial;
mso-bidi-font-family:Arial'>The 436nm g wavelength represents a deep blue
wavelength.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>lang=EN-US style='font-size:12.0pt;
font-family:Arial;mso-bidi-font-family:Arial;mso-ansi-language:EN-US;
mso-no-proof:yes'>
style='font-size:12.0pt;
font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>To follow this argument, I have set up two
lens models. One is a lens taken from a Zeiss patent to represent a 50mm
Masterprime lens. The second is a guess at a Ceg corrected lens (on axis only)
with better deep blue correction.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>A white bar pattern is computed from red,
green and blue line spread functions, as shown below. The Ceg lens has a higher
contrast blue pattern and a closer match between the red and blue images. The
Masterprime image has a higher contrast red image and a closer match between
the green and red images.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>lang=EN-US style='font-size:12.0pt;
font-family:Arial;mso-bidi-font-family:Arial;mso-ansi-language:EN-US;
mso-no-proof:yes'>
style='font-size:12.0pt;
font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The discrepancy between the colour described
by the text and the colour of the line is just a test to see that the reader is
still awake.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='text-align:justify'>style='font-size:12.0pt;
line-height:115%;font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Plots from the bar patterns show that the Ceg
lens has a greater correlation between the changes in G/(G+B+R) and B/(G+B+R),
except for two outliers. The parallel lines in the Masterprime model are caused
by aliasing in the model.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>lang=EN-US style='font-size:12.0pt;
font-family:Arial;mso-bidi-font-family:Arial;mso-ansi-language:EN-US;
mso-no-proof:yes'>
style='font-size:12.0pt;
font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>I propose that this hypothesis has some merit
and requires further study to evaluate. However, it is reliant on the artistic
preferences of cinematographers, and hence on subjective comments about image
quality. Therefore, it is difficult to define a method of deriving objective
measures.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:14.0pt;font-family:Arial;mso-bidi-font-family:Arial'>Summary
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>To
summarise focus marksstyle='font-size:12.0pt;font-family:Arial;
mso-bidi-font-family:Arial'>, they are required to measure focus consistently within
the tolerance imposed by the Depth of Field. This is usually judged by circle
of confusion of 0.01-0.025mm on an S35 sensor.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>There are variations between lenses and
aperture settings. But the lenses in a set require a consistent ÔlookÕ or aesthetic
of focus roll-off. style="mso-spacerun:yes"> And the through
focus MTF peak should be consistent with aperture setting.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Lens designs are sensitive to zonal
aberrations, which should be similar across all lenses in a set. This lack of differences
differentiates lens aberrations in the mathematical sense and demands a higher
standard of aberration compensation.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>I suggest that a suitable metric for focus ÔqualityÕ
has not been defined, particularly with regard to focus roll off.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>To
summarise ÔBokehÕ,style='font-size:12.0pt;font-family:Arial;
mso-bidi-font-family:Arial'> the consistency of aesthetic between shots is very
sensitive to small variations in wave-front curvature. And that aesthetic is
important across most of the width of the field.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Therefore a higher standard of aberration
compensation is required to match different lenses and aperture settings.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>I suggest that a metric suitable to measure
Bokeh quality does not exist.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:Arial;mso-bidi-font-family:Arial'>To
summarise colour matching,style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'> the SALT III tests show an inconsistency in
colour rendition from wide open to 2 stops down in any one lens.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>There are subtle but noticeable colour
differences that exist between different lens types wide open and at 2 stops
down. There are greater variations between the Masterprime and Summilux C
lenses when stopping the same lens down from T/1.4 to T/2.8, than between different
lenses at T/4. Therefore, colour aberrations have noticeable effect with
aperture variation.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>The effects of differences between aberration
states demand a higher state of aberration compensation, particularly zonal
chromatic aberrations.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>I suggest that a suitable metric for colour
matching does not exist.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:14.0pt;font-family:Arial;mso-bidi-font-family:Arial'>Conclusions
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Three areas have been described where quality
cine lenses have to be designed and built to standards higher than just a good
MTF
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Users vary aperture and lenses in one
photographic sequence and are sensitive to variations in ÔlookÕ. Users see lens
performance differently from optical engineers and interact with subjective and
artistic views.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Insufficient metrics are available to enable
the two groups to interact objectively.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:14.0pt;font-family:Arial;mso-bidi-font-family:Arial'>Credits
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>I wish to credit and thank the people below
for granting permission to use their work in this presentation, as well as the
people credited on the Big OLE Lens Test Party clips.
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Picture of a Monkey statue at the Natural
History Museum: Ashley Pomeroy via Wikipedia, open permission granted
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>Big Ole lens test party courtesy of Ben
Eckstein et al (Other contributors are acknowledgedstyle="mso-spacerun:yes"> in the above videos)
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>
class=MsoNormal style='margin-bottom:0cm;margin-bottom:.0001pt;text-align:
justify;mso-line-height-alt:0pt'>style='font-size:12.0pt;font-family:
Arial;mso-bidi-font-family:Arial'>SALT III lens test courtesy of Matt Hayslett
et al
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justify;mso-line-height-alt:0pt'>
style='font-size:
14.0pt;font-family:Arial;mso-bidi-font-family:Arial'>