We have touched on this
topic on several occasions. The basic
answer is “Yes”. We have also given
examples from time to time. But we are certainly
not the only ones that make those claims.
Just today I came across an article by David Taylor-Huges who discovered
some interesting difference among Leica sensors and those of some competitors. He wrote about the performance of the
Novoflex Canon EOS adapter for the Leica SL.
This gave him the opportunity to compare not only lens performance in
general, but interestingly enough the performance of Canon lenses on the Canon 5Ds
and the Sony A7rII compared to the Leica SL.
He stated:
“I have to say that I found this surprising, but these
Canon lenses are super sharp on my SL. The 17-40mm zoom, which gave me only
average results on my Canon 5Ds and soft corners on my Sony A7rII is incredibly
sharp on the SL. And so are the others, including the 18 yr.old designed
28-135mm. Of particular mention is the 85mm f/1.8, which is spectacularly sharp
across the frame. The brilliant little 40mm f/2.8 FF pancake is also very good
indeed. As I indicated, I wasn’t expecting this, but Leica’s commitment to
non-AA filtered sensors shows it’s benefits here. I’m quite happy to admit that
I’ve not been that complementary about Canon EOS EF lenses, but on the evidence
of this they are a lot better than I thought. Once you get rid of that AA
filter softness that is.
I can’t really speculate why the Sony A7rII ... I used the 17-40mm lens f/4 with was so poor, but it
was. Very soft corners and poor overall sharpness. Using the same lens with the
Novoflex adapter on the SL has shown me that there is nothing wrong with it, in
fact quite the reverse. These are focal lengths I use a lot, so I was pleased
to see the results with this lens.”
See the complete article
here:
This brings up the
question of what it is that allows the Leica sensors to show such performance
increases. The elimination of the anti
aliasing filter is one thing. Whil;e
most other manufacturers use such a filter to prevent aliasing problems, Leica
does so strictly electronically, with nothing in the way of the light path from
the lens. But there is more.
Most people are under the
mistaken impression that the higher the megapixel count in a camera, the better
the performance. Even though it may
appear to defy logic, this is not necessarily the case. Any optical system, even a theoretical one
that is made without any optical aberration or other faults, has a performance
limit.
With the ever increasing
pixel density of digital sensors, an ever increasing number of megapixels are
being put in the same space. That brings
up the question if our lenses are even capable of a level of resolution to take
advantage of the sensor’s capability.
Even the most accurately
made lenses have an absolute limit: the physical properties of light.
The resolution of any
optical system is limited by diffraction.
The light, the aperture and especially the diffraction of the light at
the edges of the diaphragm constitute an absolute limit of the overall
resolution. It is impossible to achieve
a resolution higher than that allowed by the lens, regardless of the resolution
capabilities of the sensor or film.
This brings up the
question of what resolution a photography system is capable of under ideal
conditions. This is a very interesting
question in view of the fact that many digital cameras are getting close or
even exceed the limits of diffraction – the sensors are of a resolution level
that the lenses are hardly capable of achieving. To be clear, this has nothing to do with the
quality of the lenses, it is solely because of the limits of physics.
Here is a table of these
limits based on sensor size.
The lens opening or
aperture is the deciding factor for the resolution capabilities of any optical
system. The larger the diameter in
relation to the focal length, the larger is the theoretical resolution. Each subsequent smaller aperture will half
the visible resolution.
Unfortunately, the
performance of most lenses is usually less wide open than when moderately
stopped down. The theoretical values at
f/1.4 can hardly be reached in the real world.
Optimum performance usually is not reached until stopping down to a
range of f/2.8 (at best) to f/5.6 or f/8.
Please note that due to diffusion within the emulsion these figures
extend to f/11 with most color and black and white films.
This is especially
important with smaller sensor sizes.
While a 35mm full frame sensor is capable of a theoretical resolution of
60 megapixels at f/5.6, a 2/3 sensor is reduced to just 4.4 megapixels at the
same aperture.
At this point, the actual
pixel size becomes important also. As a
rule of thumb, we use Aperture divided by 1.5 equals pixel size in microns or
µm (Aperture/1.5=pixel size). For
example, 2 / 1,5 = 1,3; 5,6 / 1,5 = 3,7.
At f/2, all sensors with a length of 1,3 µm or more on each side are
capable of resolving all the lens can deliver, but at f/5.6 the individual
pixel size has to increase to a length of at least 3,7 µm to do the same. If the individual pixel size is smaller,
resulting in a seemingly higher sensor resolution, we are dealing with a
so-called blind resolution which cannot be achieved because of the physical
limits of the resolution of the lens.
It must be pointed out
once more that these values all are based on theoretically flawless optical
systems. Not included are negative
impacts from anti-aliasing filters, signal processing (keyword Nyquist
Frequency), increases in noise and the necessary interpolation of sensors with
Bayer mosaic (RGB filters).
Ultimately it is up to
each individual what performance parameters we want to set for or expect from
our camera equipment. This article
hopefully made it clear that megapixel resolution is not necessarily the key to
overall performance of our camera equipment, that lens performance is of equal,
if not even greater importance.
This brings us to Leica
lenses in particular. Since theoretical
resolution is highest at the largest aperture of a lens, it makes sense to use
lenses which do offer good performance at those apertures. In this regard Leica lenses are
unsurpassed. While competitor lenses
might come close in performance to their Leica equivalents at smaller
apertures, their performance fall off wide open is usually noticeably greater
than with their Leica counterparts. For
example, the 180mm f/3.4 Apo-Telyt R was specifically designed to offer optimum
performance at maximum aperture. There
was no appreciable performance increase at smaller apertures. Other examples are the Summilux f/1.4 lenses
and the Noctilux f/0.95. These lenses
are capable of taking full advantage of the performance increase when used wide
open. We should always evaluate a lens
by its performance at ALL apertures and not only the ones that result in the
best results. It doesn’t make any sense
to buy a fast f/1.4 lens, for instance, if it requires to be stopped down to
f/4 or f/5.6 to deliver adequate results.
Leica 180mm f/3.4 Apo
Telyt-R and 50mm f/0.95 Noctilux
While these are compelling
reasons for considering Leica cameras and lenses, their sensors do set
themselves apart from the competition also.
Instead of participating in the pixel race, Leica and their sensor
manufacturer have done a remarkable job of optimizing sensor performance.
Compared to their
competitors, both the Leica M and S line of cameras seem to be lagging
behind. As far as total pixel count
goes, that is definitely correct.
However, that does not at all translate into lesser performance and
capabilities. The Leica sensors differ
in several respects, all of which are designed to optimize performance. Besides, what is really gained by a higher
pixel count?
Take the Leica S sensor
for instance. The difference between the
37.5 MP sensor of the Leica and a 50 MP sensor is only 10 – 15% as far as the increase in linear resolution
is concerned. Is that really enough of
an increase compared to the other advantages of the Leica MAX_24MP CMOS Sensor
as used in the Leica M? Let’s take a
closer look.
It is no secret that
individual pixel size does make a difference.
The larger the individual pixels, the better they will perform. To increase resolution, either the pixels need
to be made smaller to fit into a certain sensor size, or the sensor size needs
to be increased.
Regardless of the number
of pixels on a sensor, not the entire surface area of each individual pixel is
light sensitive. The pixels need to be
supported by a substructure and each individual pixel needs to be connected to
the system by small wires. Canon, for
instance uses wires with a size of 0.35 micron.
Sony is definitely better with a size of 0.18 micron. Leica by far exceeds that with a size of 0.09
microns. As a matter of fact, when
determining the specifications for the sensor, Leica demanded that the
structure sizes be kept as small as technically possible.
One goal was to keep the
non-sensitive areas of each pixel as small as possible. If less of the surface of the sensor is taken
up by supporting electronics overhead, then more surface area can be used to
collect incoming light. This results in greater dynamic range and a higher
initial sensitivity.
The surface of a
sensor. If the non-sensitive areas can
be made as small as possible, more surface area is gained to collect
light. Image courtesy of Leica Store Miami
Another means to increase
sensor performance is to make it as thin as possible. The Leica CMOS sensor in the Leica M240 is
the thinnest ever developed. Each sensor
contains several layers. By making each
of them as thin as possible, the end result is a significant increase in
performance because more of the incoming light can actually reach the
photodiodes, the individual pixels.
Another advantage was
gained by using copper for the connecting material instead of aluminum, which
is the common choice because the process of using copper is substantially more
complex. Copper has a substantially
lower electrical resistance than Aluminum, meaning that conducting layers with
half the thickness could be used. In
addition, to minimize thickness, instead of having four metal layers for the
conductors typically employed on CMOS sensors, only two were necessary on the
MAX CMOS chip.
An advantage was also
gained by using a different design for the microlens covering the entire
sensor. Instead of using the common flat
lenses, Leica went to an elongated, parabolic design. That has the advantage that more of the
incoming light will be redirected to the individual pixel areas and, especially
at the corners of the sensor, there will be no noticeable vignetting.
Conventional CMOS sensor
with deep pixel wells and flat microlenses
Leica CMOS sensor with
very shallow pixel wells and tall micro lenses, allowing for larger pixel area
This can easily be
verified. Several other camera
manufacturers allow the use of Leica M lenses on their cameras. Take the Sony A7r for instance. Mount a Leica 18mm Super Elmar-M ASPH on the
Sony and take a few test shots. Then
compare those to the results obtained from a Leica M. The difference is more than obvious. But it doesn't even require an extreme wide
angle lens like that. Take a 35mm
Summilux ASPH, and you will find similar difference. The Sony sensor just isn’t capable of
handling non-retrofocus lenses anywhere near as well as the Leica M does.
Therefore, when it comes
to selecting a high performance camera system, one has to decide if a gain of
two or three pixels per inch in linear print resolution is more important than
the long list of advantages gained with the Leica MAX CMOS sensor.
Some information in this
post was first used in an article about the Leica S system by Leica StoreMiami
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