Программа для измерения границ резкости

Rules of Thumb
In this chapter, we’ll collect in one place a number of the basic
concepts relevant to depth-of-field. Several of these were already listed
earlier in Chapter 5, but we’ll add a few more here.

1. If we want an object to be resolved, we make sure that
the disk-of-confusion is smaller than the object. If we
want to resolve a letter “A” on a sign where the brush
strokes forming the letter are one inch wide, we should
ensure that the disk-of-confusion is no larger than about
one inch.

2. If we want an object to be blurred out, we make sure
that the disk-of-confusion is larger than the object. If
we want to ensure that the letter “A” is not readable, we
should make sure that the disk-of-confusion is about
equal to the height or width of the whole letter.

3. Between the point of exact focus and the camera, the
disk-of-confusion can never be larger than the working
diameter of our lens. Beyond twice the distance from
lens to point of exact focus, the disk-of-confusion grows
larger than the lens opening—without limit!

4. If we want anything at infinity to be critically sharp,
focus at infinity.

5. If we want all objects of, say, 5 millimeters diameter to
be recorded—at whatever distance—we should use a
lens aperture of 5 millimeters or smaller and focus no
closer than half the distance to the furthest object. A 5
millimeter aperture corresponds to f/10 for a 50 mm
lens, for example.

6. The zone of acceptable delineation of the subject falls
equally in front of and behind the point of exact focus
(not 1/3, 2/3!).

7. Stopping down the lens one stop gives us about 40%
more depth-of-field; opening the lens one stop gives us
about 30% less depth-of-field.

8. Stopping down two stops (to double the f-number)
gives us twice the depth-of-field; opening the lens two
stops (half the previous f-number) yields half the
depth-of-field.

9. To get ten times the depth-of-field requires that we
close the lens down by 7(!) stops.

10. Depth-of-field scales linearly with distance from
camera to point of exact focus—if we don’t change
lenses. That is, the zone of acceptable sharpness about
the point of exact focus is twice as great if the lens is
focused at 20 ft than it would be if the lens were
focused at 10 ft.

11. Combining rules 8 and 10: for objects of a particular
size, the length of the zone of sharp focus is directly
proportional to a) the distance from the camera to the
point of exact focus, and b) the working f-number of the
lens. To double the depth-of-field, we can either place
the objects twice as far away from the camera, or stop
the lens down by two stops (double the f-number).

12. If we do change lenses (or zoom) to maintain the same
image magnification as the camera-to-subject image
changes and keep the lens (or lenses) set to the same
f-number, the depth of the zone of acceptable sharpness
does not change.

13. The size of an out-of-focus image of an object
corresponds to the size of the object plus the size of the
disk-of-confusion. And from this there follow the next
two points.

14. Out-of-focus images are larger than their corresponding
(lens stopped down to a pinhole) in-focus size.

15. Out-of-focus images are rounder than their in-focus
cousins.

16. The human eye can see an object which measures about
one thousandth of the distance to that object from the
eye—perhaps one two-thousandth if your eyes are
good.

17. A good normal focal length lens can resolve objects
which measure one five-thousandth of the distance to
the objects—perhaps one ten-thousandth if everything
is just right.

18. Diffraction places the ultimate upper limit on the
resolution of which any lens is capable. The general
rule is: the smallest object the lens can resolve is about
equal to the distance from lens to object divided by
1600 times the diameter of the lens opening measured
in millimeters.

19. For best resolution, film flatness typically limits the
physically largest (numerically smallest f-number)
aperture we can use reliably to about f/8 for 35 mm
cameras. And it gets worse than that (we must use even
smaller apertures) for larger formats using roll film.

20. The usual depth-of-field scale is calculated for a 1/30
mm circle-of-confusion. Typical 35 mm films and
lenses are capable of delivering a 1/150 mm standard.
To convert an existing depth-of-field scale to a new
(higher, more demanding) standard, all we have to do is
multiply the numbers on the depth-of-field scale by the
improvement factor we desire. To go for that five-fold
possible improvement, multiply all the numbers by 5:
Instead of f/2, read f/10. Alternatively, divide the
f-number you are actually using by 5 and look for that
spot on the existing depth-of-field scale: if you are
using f/11, look for the f/2.2 depth-of-field mark. And,
if you wish, you can use different standards for the far
limit of depth-of-field and for the near limit.

21. We can also easily estimate the revised hyperfocal
distance from existing depth-of-field scales. Suppose
we wish to use a figure of 1/150 mm for the diameter of
the circle-of-confusion but the scale on our lens is based
upon the 1/30 mm figure. Place the infinity mark over
the depth-of-field marker for the aperture in use, and
read off the standard hyperfocal distance at the focus
pointer. Multiply that distance by five—that’s our new
hyperfocal distance.

22. If we are using the standard depth-of-field scales (or
scales modified as suggested in 20.) and focusing the
lens at its hyperfocal distance, the disk-of-confusion at
the near limit of the depth-of-field will be one-half the
diameter of the lens opening. A further result of this is
that the actual definition of objects can get worse by no
more than a factor-of-two, between the supposed inner
limit of depth-of-field and right in front of the camera!
Take care, however, to note that this last rule applies
only if one chose to focus at the hyperfocal distance.

23. A gentle repeat reminder: when you focus at the
hyperfocal distance, you are guaranteeing that subjects
in the distance will be resolved no better than your
specified minimum standard. In order to improve upon
this, you must focus beyond the hyperfocal distance.

Ёханы бабай! Когда уже производители фотокамер додумаются такие калькуляторы встраивать в фотокамеры???

Кроме того, есть альтернативные теории посвежее,
где такие таблички не нужны:

Главное - в зоне между камерой и точкой фокусировки различимы детали размером >= линейного размера диафрагмы.
А вот за плоскостью фокусировки все может быть размыто до бесконечности.
Для получения максимальной информации о сцене стоит фокусироваться на самый дальний объект что нам нужен резким, в ближнем поле мы теряем куда меньше, чем приобретаем том самом дальнем объекте.
Чтобы разрешать ту же травку на расстоянии 200м нам нужна резкость больше на расстоянии 10м.


+очередное напоминание про то как устарели старые шкалы и таблицы ГРИП
(в основном это касается большого допустимого кружка нерезкости)

+ еще немного всякого по теме.

23. A gentle repeat reminder: when you focus at the
hyperfocal distance, you are guaranteeing that subjects
in the distance will be resolved no better than your
specified minimum standard. In order to improve upon
this, you must focus beyond the hyperfocal distance.

бред, грип элементарно рассчитывается исходя из кружка рассеяния, фокусного и диафрагмы, сам такую формулу выводил...

желаемый кружок нерезкости зависит от расстояния до объекта

бред, грип элементарно рассчитывается исходя из кружка рассеяния, фокусного и диафрагмы, сам такую формулу выводил...