Guide number

A scene will be properly illuminated for every combination of f‑stop and distance shown on this flash device’s exposure calculation dial, each of which equals the same guide number.

The guide number here (full power setting, ISO 100, and normal-angle coverage) is 37 for calculations made in meters (yellow arrow) and 120 for feet (orange). For instance, on the foot scale, f/4 × 30 ft = 120, as do both f/8 × 15 ft and f/16 × 7.5 ft. In meters, f/1.4 × 26 m = 37 as do f/22 × 1.7 m and every combination between.

In photography, the guide number, or GN for electronic photoflash devices (lighting equipment also known as “studio strobes” and “speedlights”) is a measure of their ability to properly expose a scene. Guide numbers allow photographers to quickly calculate either the required f‑stop for any given flash-to-subject distance, or the required distance for any given f‑stop.

Guide numbers are calculated as follows:^[1]

Guide number = f-number × distance

This simple relationship is well defined because the brightness of a flash declines with the square of the distance, but the amount of light admitted through an aperture decreases with the square of the f-number.^[2]

Guide numbers are not an absolute measure of illuminating power because their values are influenced by other photographic variables, notably the camera’s ISO setting and flash coverage angle (for flash devices with zoom heads).^{[note 1]} Moreover, guide numbers diminish if a photographer reduces the power setting on a flash device.

It is common for manufacturers to state guide numbers relative to a sensitivity of ISO 100.^[3] If a flash device is rated at a higher sensitivity, say ISO 200, then its guide number increases by the square root of the difference.

For any given ISO setting and coverage angle, a flash device with a guide number that is, for instance, twice as great will permit subjects to be properly exposed from twice as far away for any given f‑stop, or conversely, will permit scenes at a given distance to be properly exposed at an f‑number twice as great.

Different models of flash devices available on the market have widely varying maximum-rated guide numbers.^{[note 2]} Powerful flash devices (those with inherently greater guide numbers when compared at the same ISO sensitivity and coverage angle) are especially useful for outdoor photography because photographers can increase the maximum flash-to-subject distance when filling in shadows. See Flash fill: Guide numbers vs. distance, below. In large part, this is because the sun is such a bright, unadjustable light source against which a flash device must compete. However, a contributing factor is that many modern cameras with focal-plane shutters can sync with flash devices at speeds no faster than ¹/₆₀ th of a second. Such a relatively long exposure requires particularly small apertures and/or low ISO sensitivities, both of which constrain how far a camera and its camera-mounted flash can be from an outdoor scene, even if it is in bright shade.

Understanding guide numbers

Units of measure

Guide numbers are a composite unit of measure comprising two factors: aperture ratio and distance. Guide numbers may be expressed in either of these units of measure: f‑number⋅meters or f‑number⋅feet.

Throughout most of the world where the metric system (SI) is observed, guide numbers are expressed as a unitless numeric value like 34, even though they are technically a composite unit of measure that is a two-factor product: f‑number⋅meters.^[4] As such, guide numbers can be reduced either to distance in meters or to f‑stops depending on how one uses the guide number in a calculation.

In the U.S. however, photographers typically measure distances in feet and require guide numbers scaled accordingly. To serve the U.S. market, manufacturers of flash devices typically provide foot-based guide numbers and add nomenclature such as feet, ft, or the foot symbol ( ′ ) to unambiguously denote that fact, e.g. Guide number: 92′.^[5]^{[note 3]} Another common practice when flash devices are marketed in the U.S. is to provide two guide numbers—which can be expressed in a variety of formats—so distances and f‑numbers may be calculated using either feet or meters, e.g. Guide number: 30 m / 98 ft.^[3]

Though nomenclature conventions such as these can make guide numbers misleadingly appear to be length-based units of measure, they serve as notations to eliminate ambiguity as to which length-based system of measurement underlies the guide numbers. As with metric-based guide numbers, foot-based guide numbers are a two-factor unit of measure except the units are f‑number⋅feet.

To convert a guide number given in meters to feet, divide by 0.3048. To convert a guide number given in feet to meters, multiply by 0.3048.

Calculating with guide numbers

It is easy to use guide numbers to calculate either an aperture or a flash-to-subject distance. Consider a flash device with the following rating, all of which are the same power:

28 DIN

28 meters / 92 feet

28 (meters) / 92 (feet)

28 (m) / 92 (ft)

28 m / 92 ft.

28 m / 92′

28 / 92

92′

Suppose a photographer has a flash device with a guide number of 44 (m) / 144 (ft),^{[note 4]} sets the camera’s aperture to f/4, and wants to know the required flash-to-subject distance; he merely divides the guide number by 4. Thus, a subject 11 meters or 36 feet away will be correctly illuminated (GN 44 (m) ÷ f/4 = 11 m, and GN 144 (ft) ÷ f/4 = 36 ft). For the same guide number and an aperture of f/8, the light source must be 5.5 meters or 18 feet from the subject.

Alternatively, if one has an established flash-to-subject distance and wants to find the required f-number, one divides the guide number by the distance. Example: Guide number = 48 (m) and the distance is 6 meters; one needs and aperture of f/8 (GN 48 ÷ 6 m = f/8).

Example for finding a distance

Suppose a photographer wants to shoot with an aperture of f/2.8 and the guide number is 28 (m) / 92 (ft). The flash device must be 10 meters (33 feet) from the subject.

In metric: GN 28 ÷ f/2.8 = 10 m

In U.S. customary units: GN 92 ÷ f/2.8 = 33 ft

Example for finding an aperture

Suppose a photographer’s flash-to-subject distance is 9.75 meters (32 feet) and the guide number is 39 (m) / 128 (ft). The aperture must be f/4.

In metric: GN 39 ÷ 9.75 m = f/4

In U.S. customary units: GN 128 ÷ 32 ft = f/4

Details

An incident-light meter measures the true luminous exposure (in lux⋅seconds) illuminating a scene.

Most modern flash devices can operate at guide numbers less than their maximum ratings via either manual adjustment of their power settings in binned steps, by an in-flash automatic light sensing feature, or by being cued by the camera’s sensor; both the latter options make continuously variable adjustments. Manual attenuation settings are usually steps in powers of 0.5 (full f‑stops) that commonly extend five to eight f‑stops deep (power levels of ¹/₂, ¹/₄, ¹/₈ .... ¹/₂₅₆). To calculate how reductions in power levels affect guide numbers, see Effect of power settings, below.

The following variables must necessarily affect guide numbers in order to calculate proper exposures:

Those that affect the non-distance-related intensity of a flash arriving at a scene (a property called illuminance, measured in lux) or its duration. These are power settings, flash coverage angle, and color gels.
Those that affect the camera’s non-aperture-related light sensitivity. These are lens filters and the ISO rating of the film/imaging sensor.

Changing either the f‑stop or the flash-to-subject distance does not affect guide numbers because, by definition, choosing a different value for one factor is automatically accompanied by a reciprocal adjustment in the other.

Shutter speeds do not factor into guide number calculations and, for the most part, have no effect on electronic flash exposures. See Effect of shutter speeds, below.

Guide numbers are not affected by scene reflectance. Guide numbers are solely a measure of the illuminance and duration of a flash (lux⋅seconds) arriving at a scene as measured by an incident-light meter (pictured at right), not the amount leaving the scene.^[2] This often seems counterintuitive to hobbyists who incorrectly assume that cameras’ built-in reflected-light meters are a definitive measure of exposure. However, this principle underlies why using a camera with a through-the-lens meter to photograph a park bench surrounded by sunlit snow underexposes the image, making the bench appear nearly black and the snow as dark as grass and foliage. This is because reflected-light meters are calibrated for an average scene reflectance of 18 percent and can’t “know” when a scene has non-average reflectance. See also Gray card and Light meter.

Guide number distances are always measured from the flash device to the subject; if the flash device is detached from the camera, the position of the camera is irrelevant. Furthermore, unless a flash device has an automatic zoom feature that follows the setting of a camera’s zoom lens, guide numbers do not vary with the focal length of lenses.

Note that manufacturers of flash devices may provide guide numbers ratings specified relative to ISO 200, which increases them by 41 percent relative to those given at ISO 100.^[6] When comparing flash devices, it is important to ensure that the guide numbers are given in the same ISO sensitivity, are for the same coverage angle, and reduce to the same unit of distance (meters or feet). When these three variables have been normalized, guide numbers can serve as an comparative measure of intrinsic illuminating power rather than merely a metric for calculating proper exposures for a given scene area and camera setup.

Effect of power settings

Most modern electronic flash devices have manually adjustable power settings. Moreover, virtually all modern camera-mounted flash devices that have manually adjustable power settings also provide either a built-in mechanical circular calculator (such as shown in the photo at the top of this article) or a digital display that automatically shows the effect power levels have on f‑stop and distance (guide number).

Nonetheless, to better understand the mathematical relationship between guide numbers and power levels, consider the following formula:

Full\ power\ GN\times {\sqrt {{y}/{x}}}=Reduced\ power\ GN

…where

y

is the numerator in the fraction of the power setting

x

is the denominator in the fraction of the power setting

The following is a step-by-step example of using the above formula: Suppose your full-power guide number is 48 (it is irrelevant if it is scaled for meters or feet for this purpose) and the flash device is set to ¹/₁₆ th power. Divide 1 by 16 to obtain 0.0625. Take the square root of that (the ${\sqrt {x}}$ button on a calculator), which equals 0.25, and multiply that by the guide number of 48 to obtain a reduced-power guide number of 12.0.

The mathematical relationship between guide numbers and power levels can also be understood using the below alternative formula, which is suitable whenever the numerator in the fractional power setting is 1 (which is usually the case with flash devices):

Full\ power\ GN\div {\sqrt {x}}=Reduced\ power\ GN

…where

x

is the denominator in the fraction of the power setting

Example: Suppose your full-power guide number is 51 and your flash device is set to ¹/₃₂ nd power. Take the square root of 32 (the ${\sqrt {x}}$ button on a calculator), which equals approximately 5.657. Divide 51 by 5.657 to obtain a reduced-power guide number of 9.0.

Effect of flash angle (zoom setting)

Many flash devices have auto- or manual-adjust zoom features that permit the illumination angle to be widened (lessening the guide number) to fully illuminate the image area of wide-angle lenses, or narrowed (increasing the guide number) for telephoto lenses. Such coverage angles may be given in degrees but are often expressed as being equivalent to lens focal lengths for full-frame, 35 mm cameras. Manufacturers’ advertising practices vary as to the angle of coverage underlying their guide number ratings, in large part because some flash devices can be zoomed whereas others are fixed.

Virtually all modern camera-mounted flash devices with zoomable flash heads also have either a built-in mechanical circular calculator (such as shown in the photo at the top of this article) or a digital display; both automatically show the effect zoom levels have on f‑stop and distance (guide number).

Nonetheless, when shopping for flash devices with zoom heads, it would certainly be helpful if it were possible to mathematically convert advertised guide numbers from one manufacturer’s flash angle (zoom level) to another manufacturer’s flash angle. This is because guide numbers are often—though not always—given at their most zoomed setting and not all flash devices can zoom to the same extent.^{[note 5]}

Unfortunately, the optics of flash heads are complex; each manufacture’s designs not only have illumination areas that are slightly different, but are the product of differing relative proportions of transmission, diffusion, reflection, and refraction amongst their optical elements (flash tube, reflector, Fresnel lens, and add-on wide-angle adapter). Accordingly, there is no formula for precisely calculating how guide numbers diminish from, for instance, a 105 mm setting to 50 mm or 35 mm settings. One may consult the users guide for a specific flash device to obtain guide numbers for different zoom settings.

The below table illustrates the variation in guide numbers depending on zoom level for some select, relatively high-power zoom-capable flash devices.

VARIATION IN DECAY OF GUIDE NUMBER VERSUS FLASH ANGLE (NORMALIZED TO 105 mm) WITH SELECTED ZOOM-CAPABLE FLASH DEVICES
Flash angle^[A]	Vivitar 285	Sony HVL-F58AM	Yongnuo YN-568EX	Canon 430EX III-RT	Median value
105 mm	100%	100%	100%	100%	100%
50 mm	86%	72%	72%	77%	75%
35 mm	71%	62%	67%	65%	66%
28 mm	50%	53%	52%	56%	53%

Note A) Flash angle is equivalent to the denoted lens focal length for a full-frame 35 mm camera.

Effect of filters

Filters reduce guide numbers regardless of whether they are gels placed over the flash device or are on a camera lens. For instance a typical polarizing filter, which attenuates 1–1.5 f‑stops, will diminish guide numbers to 71–60% of their unfiltered rating.

To calculate the required reduction in guide number, use the following formula:

GN\times {\sqrt {0.5^{n}}}=Filtered\ GN

…where

n

equals the filter’s rated loss in f‑stops.

The following is a step-by-step example of using the above formula: Suppose your guide number is 32 (it is irrelevant if it is scaled for meters or feet for this purpose) and the rated loss of the filter is 1.5 f‑stops. Take 0.5 and raise it to the power of 1.5 (using the $x^y$ button on a scientific calculator), which equals roughly 0.35355. Take the square root of that (the ${\sqrt {x}}$ button), which equals approximately 0.595, and multiply that by the guide number of 32 to obtain a filtered guide number of 19.0.

The below table provides some common filter values.

ATTENUATION OF GUIDE NUMBERS WITH FILTER LOSS
f-stop loss	Factor	f-stop loss	Factor
¹/₃	89.1%	1²/₃	56.1%
¹/₂	84.1%	2	50.0%
²/₃	79.4%	2¹/₃	44.5%
1	70.7%	2¹/₂	42.0%
1¹/₃	63.0%	2²/₃	39.7%
1¹/₂	59.5%	3	35.4%

When a flash device is set to manual (M) or automatic (A) exposure mode and is not being controlled via the camera’s through-the-lens metering (TTL), a convenient way to compensate for the effect of a lens-mounted filter is to set the ISO rating on a camera to a higher value than the flash device. For instance, if a polarizing filter attenuates by 1 f‑stop and the flash device is set to ISO 100, then the camera can simply be set to ISO 200. The extra camera sensitivity compensates for the loss due to the filter.

The formula governing this relationship is as follows:

Flash\ ISO\times 2^{n}=Camera\ ISO

…where

n

equals the camera filter’s rated loss in f‑stops.

Here is a step-by-step example of using this formula: Suppose a filter attenuates by 1¹/₃ f‑stops and the flash device is set to ISO 100. Take 2 and raise it to the power of 1.3333 (using the $x^y$ button on a scientific calculator), which is approximately 2.5198, and then multiply that by 100, which equals about 252. The nearest standard camera setting is ISO 250.

Effect of shutter speeds

Shutter speeds are not a factor in the calculation of guide numbers. For most modern cameras (those with focal-plane shutters), shutter speed has no effect on flash exposures.^{[note 6]} See Shutter (photography) for more.

This is because even at the most powerful settings, flash durations seldom exceed a few milliseconds (thousandths of a second). With focal-plane shutters, a flash begins shortly after the shutter curtain has fully opened and must extinguish before the curtain begins to close. Selecting any shutter speed faster than the camera’s rated X‑sync speed, which is often between ¹/₆₀ th and ¹/₂₀₀ th of a second (from as long as 16.7 milliseconds to as little as 5.0 milliseconds) causes the shutter curtain to begin wiping closed across the film or sensor before the flash has extinguished. When this happens, an underexposed, gradated band appears along an edge of the image—often trailing off darker towards the left or bottom.

Conversely, longer exposures also have no effect on guide number. After the flash has extinguished, longer shutter speeds will only increase the contribution from continuous ambient light, which can lead to ghosting with moving subjects. See also Flash synchronization.

Flash fill: Guide numbers vs. distance

When a flash device is used for filling in shadows (flash fill) in sunlit scenes, it is capable of doing so only at distances that are a function of its guide number. The maximum guide number of the flash device establishes the maximum possible distance at which it can be used.

The below tables show the distances at which deep shadows will be filled to one f‑stop less than the sunlit portions of the scene, which is a common fill level. The tables also assume a typical sunlit brightness equivalent to exposure value (EV) 15 (at ISO 100).

—METER BASED— DISTANCE FOR A GIVEN GUIDE NUMBER (ISO 100) AT WHICH A FLASH DEVICE CAN FILL SUNLIT SHADOWS ONE F‑STOP DARKER THAN THE SUNLIT PORTIONS (SUNLIGHT = EV 15 AT ISO 100) ^{[Note B]}
GN (m)	6.5	8	10	12	15	18	22	26	30	36	45	52	60	72	76
¹/₆₀ th @ f/22	0.41 m	0.50 m	0.63 m	0.75 m	0.94 m	1.13 m	1.38 m	1.63 m	1.88 m	2.25 m	2.81 m	3.25 m	3.75 m	4.50 m	4.75 m
¹/₁₂₅ th @ f/16	0.57 m	0.71 m	0.88 m	1.06 m	1.33 m	1.59 m	1.94 m	2.30 m	2.65 m	3.18 m	3.98 m	4.60 m	5.30 m	6.36 m	6.72 m
¹/₂₀₀ th @ f/13 (f/11 +⅓)	0.72 m	0.89 m	1.11 m	1.34 m	1.67 m	2.00 m	2.45 m	2.90 m	3.34 m	4.01 m	5.01 m	5.79 m	6.68 m	8.02 m	8.46 m

—FOOT BASED— DISTANCE FOR A GIVEN GUIDE NUMBER (ISO 100) AT WHICH A FLASH DEVICE CAN FILL SUNLIT SHADOWS ONE F‑STOP DARKER THAN THE SUNLIT PORTIONS (SUNLIGHT = EV 15 AT ISO 100) ^{[Note B]}
GN (ft)	21	26	33	39	50	60	72	85	100	120	148	170	200	236	250
¹/₆₀ th @ f/22	1.3 ft	1.6 ft	2.1 ft	2.4 ft	3.1 ft	3.8 ft	4.5 ft	5.3 ft	6.3 ft	7.5 ft	9.3 ft	10.6 ft	12.5 ft	14.8 ft	15.6 ft
¹/₁₂₅ th @ f/16	1.9 ft	2.3 ft	2.9 ft	3.4 ft	4.4 ft	5.3 ft	6.4 ft	7.5 ft	8.8 ft	10.6 ft	13.1 ft	15.0 ft	17.7 ft	20.9 ft	22.1 ft
¹/₂₀₀ th @ f/13 (f/11 +⅓)	2.3 ft	2.9 ft	3.7 ft	4.3 ft	5.6 ft	6.7 ft	8.0 ft	9.5 ft	11.1 ft	13.4 ft	16.5 ft	18.9 ft	22.3 ft	26.3 ft	27.8 ft

Note B) Bear in mind that the distances shown do not conform to the the f‑number × distance formula when using the f‑stops shown in the first column because the fill level is
one f‑stop less than the sunlit portions of the scene—an underexposure. The values can only be correctly calculated by hand when the apertures shown in the first column are
larger (numerically smaller f‑number) by one f‑stop. Those f‑stops, when expressed in industry-standard nomenclature, are f/16, f/11, and f/9 (f/8 +⅓) but have the following
more precise values for calculating the above tables: f/16, f/11.3137, and f/8.9797.

As can be seen by referring to the above tables, if a photographer has a camera with an X-sync speed of ¹/₁₂₅ th of a second, is shopping for a flash device, and desires the capability to fill shadows from up to four meters (13 feet) away, a flash device with a guide number of at least 45 (m) / 148 (ft) will be required.

Note that increasing the ISO sensitivity of the camera will not increase the distances given in the tables because the extent to which ISO settings affect the exposure in the flash-filled areas of an image will equally affect the sunlit ones. A flash device can only fill shadows to 50% the brightness of the sun (1 f‑stop of attenuation) out to a certain distance; at a camera’s X‑sync shutter speed, no change in ISO settings—and resultant f‑stop settings—can influence this proportional relationship.

Notes

↑ Studio strobes in particular are often rated in watt⋅seconds, which is an absolute measure of illuminating power but is not particularly useful for calculating exposure settings.
↑ For example, amongst hot shoe-mounted speedlights, at ISO 100, 60° horizontal coverage angle (suitable for use with a 35 mm-format, full-frame lens with a 35 mm focal length), and full power, the Holga Holgon MF Flash has a guide number of 6.5 (m). Under the same conditions, both the Sony HVL-F58AM and the Metz mecablitz 64 AF-1 digital have guide numbers of 36 (m). And still under the same conditions, the side-mounted pistol grip-style Metz mecablitz 76 MZ-5 digital is rated at 45.5 (m).
↑ Bold typestyle is not a required convention for denoting guide numbers. Bolding is consistently used throughout this article to unambiguously distinguish the text and measures being discussed.
↑ The dual-scale format used for many examples of guide numbers within this article (similar to the practice observed by Metz mecatech GmbH and others) is purely a matter of style. It is used here not only because it is relatively compact, but because by observing the convention of enclosing the symbols for length within parentheses, it is clear they are notations as to the measurement system underlying the guide numbers and don’t misleadingly appear to be units of measure for length with their accompanying numeric magnitudes.
↑ Another not-uncommon marketing practice is to rate flash devices for a coverage angle suitable for use with a 35 mm-format, full-frame lens with a 35 mm focal length (a flash coverage angle of 60° horizontally).
↑ A notable exception to this generality is when a flash device at full power is used in combination with cameras equipped with leaf shutters set to very brief exposure times.

References

↑ B & H Foto & Electronics: Understanding Guide Numbers
1 2 Scantips.com: Understanding Flash Guide Numbers, plus GN Calculator
1 2 One notable way for expressing guide numbers scaled for use with both feet and meters (and relative to an ISO setting of 100) is as practiced by Metz mecatech GmbH, as exemplified by the data sheet for their mecablitz 52 AF-1 digital (product page here):
Flash output
• High max. guide number 52 (meters), High max. guide
number 170 (feet) for ISO 100/21° and 105 mm
Another notable example is Nikon’s practice for expressing the technical specifications of products marketed in the U.S., such as their SB-5000 AF Speedlight (product page here):
Guide Number
34.5 m/113 ft. (at 35 mm) 55
m/180 ft. (at 200 mm) (FX
format, standard illumination
pattern) (at ISO 100)
Yet another notable example is Canon USA’s practices, as exemplified by their Speedlite 430EX III-RT (product page here), which is as follows:
Guide Number The maximum Guide No. is approximately 141.1 ft./43m at ISO 100 and 105mm flash coverage.
↑ The style for expressing guide numbers throughout the metric-observing world is typified by the practices of Metz mecatecheh GmbH, as exemplified by the German-language version of their website for their mecablitz 76 MZ-5 digital (product page specifications here):
Blitzleistung
• Hohe max. Leitzahl 76 bei ISO 100/21° und 105 mm
This translates to English as follows:
Flash output
• High max. guide number 76 at ISO 100/21 ° and 105 mm
↑ One example of using the single-prime (foot symbol) when marketing in the U.S. is as practiced by Bolt, which specifies the guide number of their VS 510P (product page here) as follows:
The VS-510P Wireless TTL Shoe Mount Flash from Bolt is a dedicated TTL flash for use with Pentax & Samsung DSLR, mirrorless or point-and-shoot cameras. The VS-510 features a guide number of 141' at ISO 100 and an adjustable tilt head with five positions: 0 to 90°.
Another notable example of how flash device guide numbers are communicated to the U.S. market is the large retailer, B & H Foto & Electronics (on-camera flash page here), which states guide numbers formatted like this example for Nissin’s i60A:
• Guide Number: 197' at ISO 100 and 200mm
↑ Nikon, for instance, gives two ratings when providing the technical specifications for their SB-910 AF Speedlight, one of which is relative to ISO 200 (product page here):
Guide Number
34 m/111.5 ft. (at ISO 100,
35mm zoom head position, in
FX format, standard
illumination pattern,
20°C/68°F) to 48 m/157.5 ft.
(at ISO 200, 35mm zoom
head position, in FX format,
standard illumination pattern,
20°C/68°F)

External links

Scantips.com: "Understanding Flash Guide Numbers, plus GN Calculator"

Photography
Outline
Terminology	35 mm equivalent focal length Angle of view Aperture Black and white Chromatic aberration Circle of confusion Color balance Color temperature Depth of field Depth of focus Exposure Exposure compensation Exposure value F-number Film format Large Medium Film speed Focal length Guide number Hyperfocal distance Metering mode Orb (optics) Perspective distortion Photograph Photographic printing Photographic processes Reciprocity Red-eye effect Science of photography Shutter speed Sync Zone System
Genres	Abstract Aerial Architectural Astrophotography Banquet Conceptual Conservation Cloudscape Documentary Ethnographic Erotic Fashion Fine-art Fire Forensic Glamour High-speed Landscape Lomography Nature Neues Sehen Nude Photojournalism Pornography Portrait Post-mortem Selfie Social documentary Sports Still life Stock Street Vernacular Underwater Wedding Wildlife
Techniques	Afocal Bokeh Brenizer Contre-jour Cyanotype ETTR Fill flash Fireworks Harris shutter HDRI High-speed Holography Infrared Intentional camera movement Kirlian Kite aerial Long-exposure Macro Mordançage Multiple exposure Night Panning Panoramic Photogram Print toning Redscale Rephotography Rollout Scanography Schlieren photography Sabatier effect Stereoscopy Stopping down Strip Slit-scan Sun printing Tilt–shift Miniature faking Time-lapse Ultraviolet Vignetting Xerography
Composition	Diagonal method Framing Headroom Lead room Rule of thirds Simplicity
Equipment	Camera light-field field instant pinhole press rangefinder SLR still TLR toy view Darkroom enlarger safelight Film base format holder stock Filter Flash beauty dish cucoloris gobo hood hot shoe monolight Reflector snoot Softbox Lens Wide-angle lens Zoom lens Telephoto lens Manufacturers Monopod Movie projector Slide projector Tripod head Zone plate
History	Timeline of photography technology Analog photography Autochrome Lumière Box camera Calotype Camera obscura Daguerreotype Dufaycolor Heliography Painted photography backdrops Photography and the law Glass plate Visual arts
Digital photography	Digital camera D-SLR comparison MILC camera back Digiscoping Digital versus film photography Film scanner Image sensor CMOS APS CCD Three-CCD camera Foveon X3 sensor Image sharing Pixel
Color photography	Color Print film Reversal film Color management color space primary color CMYK color model RGB color model
Photographic processing	Bleach bypass C-41 process Cross processing Developer Digital image processing Dye coupler E-6 process Fixer Gelatin silver process Gum printing Instant film K-14 process Print permanence Push processing Stop bath
Lists	Most expensive photographs Photographers Norwegian Polish street women
Category Portal

This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.

Guide number

Understanding guide numbers

Units of measure

Calculating with guide numbers

Example for finding a distance

Example for finding an aperture

Details

Effect of power settings

Effect of flash angle (zoom setting)

Effect of filters

Effect of shutter speeds

Flash fill: Guide numbers vs. distance

See also

Notes

References

Further reading

External links