FOCUSING
TESTS
or
HOW
TO PROVE THAT YOUR CAMERA CANNOT FOCUS
@ 1983 The
Anstendig Institute
PREFACE
According to Ansel Adams, "When we say an image is sharp or in
focus, we mean that, theoretically, the light rays from anyone point on the
subject are converging at a corresponding infinitesimal point in the image of
the focal plane.1 This is quoted by Joseph Dahl, Oct. 20, 1962, in
his application for a U.S. Patent, which was granted August 30, 1966, for his
absolutely focal-point-exact focusing device Messraster. Mr. Dahl then explains
that, in the applied-for patent "this theoretical assumption has become a
reality" and that "instead of the heretofore permissible diameters of
the circle of confusion of 1/lOOOth part of an inch,
i.e., or an area of 314 mu, the now produced minute
bundles of rays have only an area of .078 mu."
(One mu is 1/lOOOth of a
millimeter.) What that means is that lenses were already capable of performance
that achieved that theoretical infinitesimal point but, due to the inaccuracy
of available focusing systems, one never got to see that performance. The
advent of the focal-point-exact Messraster made it possible to realize the true
definition of focusing which in turn, for the first time, showed the high
performance that good lenses are capable of.
Dahl continues: "As to depth of field",
The present invention teaches that such "tolerances of
image definition" represent optical physical non-realities and have now
been eliminated. Instead, there is now given the possibility of the point/true
focusing."
The text goes on to say that the invention also allows the
precise determination "of the true optical destination of depth of
field". In other words, even if one accepts depth of field as meaning
more-or-less tolerable UNSHARPNESS, it remains meaningless unless one can
precisely determine (focus on) the exact subject-plane in front of and in back
of which the depth of field is to extend.
The above-mentioned patent has been known to the optical and
camera industries for decades and has not been brought out, although, by the
time of the inventor's death, some highly respected manufacturers wanted to
deliver it for their cameras (Exakta, Hasselblad, Nikon, Killfitt).
Mr. Dahl maintained until his death that the German optical industry, which he
said was at that time controlled by Zeiss Ikon and the Carl Zeiss
industrial empire, fought the introduction of his invention from the start
because it made their own focusing devices obsolete, refuted most of the
technical ideas they had endorsed, and demanded greater precision in their
cameras. What Mr. Dahl did not say was that it must have been obvious to the
industry that, if the Messraster were introduced and the public understood its
full implications, everyone interested in best picture quality would have
wanted it, and one man, the owner of the patent, would have had control over
the entire industry. With the death of Joseph Dahl in 1970, that threat
disappeared, and it is The Anstendig Institute's firm belief that it is now
time
- for the
true physics of focusing to be made known,
- for the
manifold wrong beliefs upon which the whole field of photography is based
to be exposed and corrected,
- for the
public to become aware that a possibility of real, absolutely exact
precision in picture-taking exists,
- for
manufacturing the Messraster and making it available to all those
interested in precision since it is no more difficult to manufacture than
most of the presently available auxiliary focusing screens on the market.
This paper describes simple tests with which everyone can, for
themselves, prove the greatest hidden scandal in present-day industry: that
none of the multi-millions of cameras that are available or being manufactured
are capable of doing what the word "focusing" means and that their
capabilities extend only within the narrow range from totally inexact to
impossible-to-focus-at-all. If someone does not own a camera, it would still be
instructive to go to a photo store and try these tests with a reputable camera.
THE TESTS
GROUND GLASS
For this test
one can use either a focusing screen that is only a ground glass or one can use
the ground glass part of combination focusing screens that have other devices
in the middle.
First, cover a waist-high table with a newspaper (see diagram A
at the end of this paper). Then, as in the diagram, stand two or three feet
away from the table and point the camera down at a part of the newspaper about
a foot or so from the edge of the table and try to focus. One will immediately
notice that, instead of clearly seeing a sharpest point, one sees a whole
stretch of print that appears sharp in front of and in back of the point upon
which one is trying to focus. Somewhere in that stretch is the really sharpest
point that one should be able to determine with any focusing device, but one is
unable to do so because neither the ground-glass nor one's eyes can
differentiate (resolve) that point. But the film and the lens can resolve it,
and it would be clearly seeable if one took a picture (without shaking the
camera, of course). That stretch, within which no focusing is possible because
everything looks sharp, is the well-known limitation of the focusing precision
of the ground glass, the limitation that caused the optical industry to seek
other means of focusing. Trying the same test with other focal-length lenses
and with different aperture openings (by manually stopping down the lenses)
will provide a more complete picture of the impossibility of achieving
precision with a ground glass. But the same test can be readily carried out
with the SLR focusing grid and with the non-SLR rangefinder cameras with similar
results.
SLR FOCUSING GRID
The same test
can be made with the prismatic focusing grid in the middle of many focusing
screens. The disturbing prismatic grid is supposed to disappear when focus is
achieved. But notice over how long a stretch of the newspaper it seems to
remain invisible (I say seems, because some flicker is always still present, if
not very noticeable). That stretch is the distance within which it is
impossible to focus with this system...the tolerances that define the system's
inaccuracy. Repeating the test as above, with other focal-length lenses and
with different aperture openings (by manually stopping down the lenses) will
give the tester much to snicker about.
NON-SLR RANGEFINDER CAMERA
This test is
for rangefinder-focusing cameras of the type in the original Leica and in many press-type cameras (not through-the-lens,
split-image range-finders). Look at the newspaper through the rangefinder: try
to focus until the two images fuse at the point in the text on which you want
to focus and notice how many lines above and below that line the double image
remains together. It should be said that, with a well-made rangefinder of this type,
the front-to-back range within which no more focusing can ensue is narrower at
short distances than with SLR focusing systems. But the farther away one gets,
the less accurate the rangefinder becomes until at somewhere between 5 and 15
meters, depending on the camera, the lens is at infinity and beyond that
distance, the two images for everything visible in the rangefinder remain
together. Of course, with this system, one does not even see the image as it
will appear on the film, and it does not work on really short distances under
about 2 feet.
SLR SPLIT-IMAGE RANGEFINDER
For this test
find a long, vertical black or dark-colored line that stands out clearly
against its background (the crack in a door, the edge of a door, the edge of a
cabinet, a hanging wire, etc.). Then, as in diagram B, aim your camera at a
point in the middle of the line, cut it with the dividing line of the
rangefinder, and focus until the two sides of the line come together. Now,
slowly raise or lower the angle of the camera while keeping the rangefinder on
the line and notice how far you can go above and below the place on which you
had originally focused without the images separating. You can also try slowly
moving your head closer to and farther away from the line and notice how far
you can move back and forth without the lines separating. If that does not
already have you either snickering or furious, try using other focal-lengths
and/or manually stopping the lenses down. At some smaller aperture (but still
large enough that one should expect to be able to focus with it), the
rangefinder just blacks out and becomes nothing less than an annoying disturbance. The first test can be tried by those who use
the seldom encountered clear-glass circle with hairline cross. While somewhat
more accurate than the ground-glass, this system will still show more
tolerances than its reputation for accuracy would suggest. One should not
forget that one's eye vacillates and seldom continues to see the aerial image
exactly at the plane of the hairline cross, and that the system has a built-in
error if the clear-glass surface is flush with the surface of the ground glass
that it is in the middle of.
Variations of both the first and second tests can be attempted
using auto-focusing systems. The results will probably be hilarious, without
even bringing up the question of how one is supposed to direct those systems at
a single point, like the pupil of an eye, or at a thin wire, etc.
Amazingly, today, in 1983, cameras that have no focusing system
at all are still being produced in enormous numbers. This arrangement was used
in the early beginnings of photography only because no portable method of
focusing existed. An anachronism in the true sense of the word, these cameras
were already indefensible with the introduction of the first primitive
range-finder and SLR cameras. The camera buyer has the right to decide that
he/she does not want to bother with focusing, but only after the buyer has been
made aware that, under such circumstances, only the worse possible, most
unacceptable results can be depended on and not fooled into thinking that being
able to focus is just one more feature that does not make much of a difference.
Any honest person who tries these tests will immediately
understand that there is no way one can speak of accuracy in the whole realm of
photography. The point of photography is to get an accurate image onto the
film, and it does not matter how wonderful the camera body or the lens is if no
precise possibility of getting them together is available. What, pray tell, is
the logic of touting shutters, lenses, electronic exposure controls, etc., as
amazingly precise wonder-works and not expecting EVEN MORE PRECISION from the
most important part of photography, the focusing system? Since the inaccuracies
of the available focusing systems are well-known, but unmentioned in the
industry and the industry-controlled photographic press, the logical conclusion
is that the public is being manipulated to believe that the inaccuracies they
have to put up with are good enough and that there is no need for exact
focusing because it does not make any real difference. It can easily be proved
that focal-point-exact focus DOES make a difference...an ENORMOUS difference in
EVERY aspect of picture quality. In other words, the public is being fooled.
1 Ansel
2 Ibid., page 37.
The Anstendig
Institute is a non-profit, tax-exempt, research institute that was founded to
investigate the vibrational influences in our lives and to pursue research in
the fields of sight and sound; to provide material designed to help the public
become aware of and understand vibrational influences; to instruct the public
in how to improve the quality of those influences in their lives; and to
provide the research and explanations that are
necessary for an understanding of how we see and hear.
Related papers explaining in detail what focusing should really
be and why are available free of charge from The Anstendig Institute.
DIAGRAM A
DIAGRAM B