Aperture row (optics)

Aperture row is a term from photography and optics . It describes the entirety of all possible aperture settings of a lens , sorted from the largest to the smallest aperture.

F-number

The f-numbers are relative values that result from dividing the focal length f by the diameter of the entrance pupil ( opening width ). The complete notation of the geometric f-number (BZ) was accordingly f / (BZ); “F / 4” corresponds to the aperture number 4 specified for camera lenses.

The value with the aperture fully open is called the light intensity . A lens with a focal length of 2 has an effective aperture of 25 mm at a focal length of 50 mm; the entrance pupil of a 135 mm telephoto lens therefore has an effective aperture of 67.5 mm with the same f-number.

With smaller image sizes, such as the Micro Four Thirds format with a format factor of two in relation to the full format , the opening width is halved for the same angle of view and the same light intensity in relation to the smaller sensor, since the focal length for the same image size is only half as long is. Small image sizes thus enable the construction of relatively small, bright lenses.

The f-number is the denominator of a fraction ; this explains the apparent contradiction that a larger f-number indicates a smaller aperture.

Today's aperture range

Setting scale of an older exposure meter with aperture row and two shutter speed rows

Whole f-stops

The row of diaphragms is designed in such a way that the amount of light falling through the lens varies from f-stop to f-stop

... halved if the next f-stop has a higher value (for example 11 → 16) or

... doubled if the next f-stop has a lower value (for example 11 → 8).

The aperture diameter D increases or decreases from aperture to aperture by the factor √2 or 1 / √2, which means that the area and the amount of light are doubled or halved. This gradation corresponds to the usual exposure time series and thus enables the aperture and exposure time to be easily adjusted with the given lighting.

Each f-number k is calculated from the previous one by multiplying it . Accordingly, any f-stop can be calculated using the formula . The mathematically exact values, however, do not exactly match the usual aperture series convention. Usually the f-number is given rounded to one or two digits so that the following series results: ${\ displaystyle {\ sqrt {2}}}$ ${\ displaystyle k = ({\ sqrt {2}}) ^ {(n-1)}}$ ${\ displaystyle n = 1,2,3 ...}$

f /	0.5	0.7	1	1.4	2	2.8	4th	5.6	8th	11	16	22nd	32	45	64	90	128
arithmetically	0.5	0.707 ...	1	1.414 ...	2	2.828 ...	4th	5.657 ...	8th	11.31 ...	16	22.62 ...	32	45.25 ...	64	90.51 ...	128

Half f-stops

Half aperture stops

The half-stop increments can use the formula to be calculated, resulting rounded: ${\ displaystyle k = ({\ sqrt [{4}] {2}}) ^ {(n-1)}}$ ${\ displaystyle n = 1,2,3 ...}$

f /	0.5	0.6	0.7	0.85	1	1.2	1.4	1.7	2	2.4	2.8	3.4	4th	4.8	5.6	6.7	8th	9.5	11	13	16	19th	22nd	26th	32
arithmetically	0.5	0.594 ..	0.707 ...	0.840 ...	1	1.18 ...	1.41 ...	1.68 ...	2	2.37 ...	2.82 ...	3.36 ...	4th	4.75 ...	5.65 ...	6.72 ...	8th	9.51 ...	11.3 ...	13.4 ...	16	19.0 ...	22.6 ...	26.9 ...	32

Similarly, a f- number can be calculated by multiplying (or ) by its previous f-number. ${\ displaystyle k}$ ${\ displaystyle {\ sqrt [{4}] {2}}}$ ${\ displaystyle 2 ^ {(1/4)}}$

Many manual lenses have half steps on the aperture ring . As a rule, they are not labeled separately.

Third f-stops

Here is the formula with . Applied and rounded: ${\ displaystyle k = ({\ sqrt [{6}] {2}}) ^ {(n-1)}}$ ${\ displaystyle n = 1,2,3 ...}$

f /	1	1.1	1.2	1.4	1.6	1.8	2	2.2	2.5	2.8	3.2	3.5	4th	4.5	5.0	5.6	6.3	7.1	8th	9	10	11	13	14th	16	18th	20th	22nd	25th	29	32	36	40	45
arithmetically	1	1.122 ...	1.260 ...	1.414 ...	1.587 ...	1.782 ...	2	2.245 ...	2.520 ...	2.828 ...	3.175 ...	3.564 ...	4th	4,490 ...	5.040 ...	5.657 ...	6.350 ...	7.127 ...	8th	8.980 ...	10.08 ...	11.31 ...	12.70 ...	14.25 ...	16	17.96 ...	20.16 ...	22.63 ...	25.40 ...	28.51 ...	32	35.92 ...	40.32 ...	45.25 ...

Modern cameras are often able to set one-third f-stops. This is usually done electronically using a dial on the camera or the camera's automatic exposure . Third steps or other different values are often specified to the initial opening ( light intensity ) to describe lenses if they do not coincide with a full f-stop. For example, many standard zoom lenses have an initial aperture of 3.5 to 5.6, depending on the focal length.

Old row of apertures

The so-called old aperture series common before the Second World War used the f-number 3.2 (root of 10) as the basis and had the following gradation:

1.1 - 1.6 - 2.2 - 3.2 - 4.5 - 6.3 - 9 - 12.5 - 18 - 25 - 36 - 50 - 71 - 100

The series of diaphragms of the Minolta-Flex (1936), a two-lens reflex camera for roll film of the type 120 and the recording format 60 mm × 60 mm, has a special feature : a mixture of the "old" and "new" series of diaphragms is engraved on it:

3.5 - 4.5 - 5.6 - 8 - 11 - 16 - 25

Many older cameras and lenses, as well as lenses for film cameras , do not have a latching diaphragm, and it is also common for lenses for magnifying devices to be able to switch off the latching diaphragm so that any intermediate values can be set.

literature

DIN ISO 517: 2009-05: Photography - aperture ratios and related sizes in camera lenses - designations and measurements

ISO 517: 2008-03: Photography - Apertures and related properties pertaining to photographic lenses - Designations and measurements

DIN 4522-11: 2015-06: Taking lenses - Part 11: Labeling and preferred values

Individual evidence

[1] Picture of a Minoltaflex with the serial number 22843: taking lens and central crown lock.

[2] ture of a Minoltaflex.