In a television advertisement
a while ago the statement was made that, if it is on the internet, it must be
true. I was reminded of that a couple of
days ago when I read an article comparing film to sensor resolution. The writer boldly stated that most films have
a resolution of at least 300 l/mm (lines per millimeter). Of course that was overstating things by a
huge margin. I don’t mean to say that
there aren't films that can attain such high resolution figures, but all films?
Resolution is generally
tested by taking photographs of test targets which show a pattern of black
lines in an ever decreasing size against a white background. Eventually the lines will become so small
that the film, or the lens, can no longer distinguish the black lines from the
white spaces in between. One black line
and the adjacent white space are referred to as 2 l/mm or 1 lp/mm (line pair per
millimeter).
Typical test target
It is a known fact, however,
that evaluating resolution with test targets does not render very conclusive
information. The black lines and white
spaces in between constitute a very high contrast. This makes it substantially easier for the
film (or a lens) to separate the two.
Reducing contrast by using grey lines on a white background would render
substantially different results.
Another major factor
influencing resolution is the grain structure of the film. A film image is made up of silver halide clumps which show up in form of grain. The smaller the silver halide clumps or the grain, the finer the detail that can be shown. Faster films simply do display coarser grain
which in turn lowers the resolution of a film.
These three images are from a fine grain negative (Agfapan APX 25).
The first was scanned from an 8x enlargement, showing the entire negative area.
The second image was scanned from a 16x enlargement.
The third shows a cropped section of the same 16x enlargement
Grainy film image. The grain is so large that small detail simply cannot be shown
Photo: Góry Bialskie
For comparison: Full image and cropped section from a 5 megapixel digital camera (Leica Digilux 2)
Finally, the structure of the
emulsion or emulsion layers influences film resolution because in any case,
light traveling through the emulsion, will scatter and thus reduce resolution
as well.
Subsequently, to say that
most films have a resolution of 300 l/mm is patently false. As a matter of fact, only few commercially
available films even have that high a resolution.
Researching this topic, I
came across a report written by Joseph A. Schantz, Assistant Head of Research
and Development Department at the Navel Photographic Center in Washington, DC. He wrote that since 1963 the Navel
Photographic Center and the Navel Air Systems Command as a matter of continuous
policy have expanded efforts to upgrade 35mmphotography on a systematic
basis. The aim of this work was not only
to improve the quality of documentary and reportage photography but also to
improve intelligence collection capabilities of the Navy’s cameras.
According to the research
done by Mr. Schantz, the best resolution obtainable with conventional, slow
speed films, like the old Agfapan APX 25, is 250 – 300 l/mm compared to 550
l/mm with the Agfa High Contrast Copy Film and 600 l/mm with Kodak 5069 and
3414 film.
Kodak High Contrast Copy Film
when processed in the POTA developer of Marilyn Levy (Levy, M., “Wide Latitude
Photography,” Science and Eng. Vol. II Number I, January, February 1967) yield
excellent high resolution negatives with adequate film speed. The Agfa High Contrast Copy film gives a
practical combination of good resolution and emulsion speed.
In addition, C. B. Neblette
in his book “Photographic Lenses” clearly states: The resolving power of a
lens-film combination is not fixed by the film alone, but by both the lens and
the film (or sensor). Resolution is determined principally by the sharpness of
the image (lens resolution). But it is
profoundly influenced by the tone producing properties of the receptor (film or
sensor) and its ability to reproduce steep gradients. For that reason resolution cannot be regarded
as an exclusive property of the lens.
For the average films
available today, a more modest resolution of 100 to 200 l/mm is a realistic
figure, based on film speed and general properties of the film. Black and white films generally have a higher
resolution than color films. The former
Agfapan APX 25, for instance, had a resolution close to 300 l/mm while Fuji
Velvia 50 is rated to resolve 160 l/mm.
To make film resolution more
understandable in this comparison, let’s refer to the smallest detail a film
can show as pixels. On a standard 24 x
36mm 35mm frame, a film with a resolution of 100 l/mm would render a total of over
8,6 million pixels. That increases to over
19,4 million pixels with a film resolution of 150 l/mm and over 34,5 million
pixels with a 200 l/mm resolution.
Of course a 35mm negative or
transparency is of little use just by itself.
Today transparencies generally are scanned and then further processed
digitally. Does anyone still use a slide
projector? Many film users still make
their own enlargements, mostly from black and white negatives, or the negatives
are scanned for further processing.
Regardless how films are used, any further processing will have an image
degrading effect, based on the slide projector, enlarger or scanner used and by
their respective quality.
For more details on this
topic go to LEICA Barnack Berek Blog article “LEICA LENSES – WHAT GIVES THEM
THEIR OUTSTANDING QUALITY.”
How does this compare to
digital sensors? Top level full frame
(24 x 35mm) cameras currently have resolution levels of approximately 25 to 35
megapixels, with higher pixel counts to be expected in the near future. The general belief is that the higher the pixel
count, the better the image quality.
However, there is a lot more to that than meets the eye. The new CMOS sensor in the Leica M (Typ 240) has definite advantages over conventional CMOS sensors. For a more detailed description of digital
sensors and some of the major differences, got to LEICA Barnack and Berek Blog article “THE PIXEL RACE - DOES IT REALLY MAKE SENSE?”
Section of a typical sensor
Image courtesy of Red Dot Forum
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
Unlike film, digital sensors
will render the same contrast level up to the finest detail. This has the result that the finest detail becomes less visible. A color image is made up out of RGB (red, green,
blue) image elements. With the exception
of the hardly ever used Foveon sensors, digital sensors can record only in black
and white. In order to obtain a color
image, the light passes through an array of red, green and blue filters, the
Bayer filter grid. This means that the
total number of pixels in a sensor are exposed to either red, green or blue
light only. To form a color image, the
information obtained from the sensor is then processed by interpolation in the
camera or by raw conversion software. It
takes the pixels of each color, and assigns all colors to each pixel. With other words, the software will take a
red pixel, for instance, and assign theoretical green and blue values as well to form a
complete color image. As good as these
types of software have become, there are certain losses involved.
With lower quality cameras
these losses can be as much as 50 percent of the resolution. The only exception to this is the Leica M
Monochrome. Here the Bayer filter and
interpolation software is eliminated to record just black and white
images. See LEICA Barnack and Berek Blog article “MONOCHROME SENSOR - WHAT IS THE DIFFERENCE.” The result is an unsurpassed
image quality and tonal range.
In the final analysis, just
as there are definite performance differences among films, there are also considerable
differences among sensors. CCD sensors used
to be the choice of most camera manufacturers.
These have been widely replaced by CMOS sensors. In this respect, Leica is no different. Many people are under the mistaken impression
that the CCD sensor in the Leica M9 delivers superior results than the current
CMOS sensor in the Leica M (Typ 240) A
recent comparison test by David Farkas of the Leica Store Miami thoroughly
debunked that. He took this very subject
to task in a three part series in the Red Dot Forum (www.reddotforum.com). See LEICA Barnack Berek Blog article “LEICA M
(TYP 240) VS LEICA M9”.
The debate of which is
better, film or digital sensors, cannot be answered with any certainty because
the large differences among films and sensors.
What can be said is that both film and sensors are capable of delivering
very high quality images. In many cases
they do exceed the requirements of the photographer since extreme cropping or
enlarging is necessary to even reveal the limits of their capabilities. Thus it is more a matter of personal choice
than effective differences pointing to one or the other medium as being
superior.
As for myself, I used to
spend many hours in my lab developing films and printing with a Leitz Focomat
V35 as well as medium and large format enlargers. Having switched to digital, I don’t
miss analog photography at all, and I can say with certainty that I am not
compromising the overall quality of my work by having done so.
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Here we talk about digital camera high range, with sensors and optics at the top of what the market offers. I think it depends very much on the film format. With an average size of Hasselblad and Zeiss optics (to stay in the top range) there is no sensor that takes ... If then we go to the optical bench with large slabs, becomes impossible any comparison with digital. In 35 mm already 6 or 7 megapixel cmos or ccd have more detail (slightly above the CCD, although slower and energy-hungry) ... In any case also depends greatly on the film speed and the accuracy of the development. I would not go beyond certain comparisons. For now though sensors with the same "soul" of a film I do not see.
ReplyDeleteI argue that in fact already '6 or 7 mpx are substantially higher in definition to the classic film 135mm. On this we agree. On HST and Pan-STARRS are mounted ccd for astronomical use. if you have not opted for cmos will have their reasons ... The lack "soul" of the sensor and 'linked to the nature of the raw files that must collect the most information in a "neutral" to allow then the most' ample opportunity 'to obtain quality images' .... But to get this often serve hour work PC. I do not make matters any better / worse. I think everyone works with the means that more 'the own pace. I just think some comparisons leave the time they are ... I work in both analog and digital, but I choose to use the technique based on the type of photos that I have to do. Different techniques for different emotions. Professionally work only in digital. For more photos and my personal use almost exclusively analog.
ReplyDeleteI see that ultimately our opinions are not very different from each other. I work only digitally. That, however, does not mean that I do not appreciate film. I simply don't like to take the time any longer that is necessary to develop and print (or scan) negatives and transparencies.
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