What Gn Is On Camera Flash?

Flash Guide Number

Digital SLR Flash

The flash guide number tells you - in a general sense - how powerful the flash is and hence, how much of an area information technology can illuminate.

Put another mode:

• If your goal is to take intimate portraits in a small room, you don't need flashes with huge guide numbers
• If information technology's your intention to photograph the interior of cathedrals, then you do

These are clearly extreme examples - for many photographers the most mutual utilize for a wink will be somewhere in between.

While the data on this folio probably won't assist you nothing in on the exact guide number you demand, a ameliorate understanding of flash guide numbers volition aid clarify why i flash can cost $100 and some other can cost $400.

Distance, Aperture and ISO

In social club to understand how a wink guide number is calculated, you first have to empathise 2 common digital SLR photographic camera settings: discontinuity and ISO.

1. Aperture is the width of the opening in the photographic camera's lens - a wider discontinuity allows more calorie-free to land on the camera's sensor
2. ISO indicates how much light the sensor can blot - the higher the ISO number, the more light the sensor absorbs

Apertures are measured in f-stops, and at that place'south a common calibration for them:

1.4

2.0

2.8

4.0

5.vi

8.0

11

xvi

22

32

From left to right the apertures are decreasing in size. This means that an aperture of f/i.4 is wide open while an aperture of f/32 is quite narrow.

There's as well a common calibration for ISO numbers:

100

200

400

800

1600

3200

At ISO 100 the photographic camera is not very sensitive to low-cal and at ISO 3200 it is VERY sensitive and absorbs light rapidly.

So what does this all accept to do with flash guide numbers?

A Counterbalanced Exposure

Regardless of the amount of available light, every photo that yous take tin can turn out one of iii ways:

1. Under exposed — likewise dark
2. Over exposed — too bright
3. Correctly exposed — the right balance of night and lite

Ideally, yous'd similar to capture photos that look like #iii all the time - but this is sometimes difficult when the bachelor light is very dim.

When there's not a lot of low-cal to piece of work with, you can:

1. Open up the lens aperture very wide
2. Increase the ISO setting
3. Enable the flash

When taking photos in dim low-cal, you tin sometimes go away without using a flash just by opening the lens discontinuity and increasing ISO. In this case, yous're just setting the photographic camera to absorb every ounce of available lite to create a good exposure.

When you enable the wink, you're introducing a SECOND light source into the photo, and this calorie-free can either supplement the available lite or overpower it completely.

The guide numer is an indication of a flash'southward power to overpower ambient calorie-free and burnish your discipline.

Flash Guide Number Formula

At that place's a mathematical formula for calculating wink guide numbers:

Guide Number = [Flash to Subject Distance] 10 [F-Stop]

Earlier we dig into some examples, it's important to note the following constant in the equation: ISO. When a guide number is calculated, it is often assumed that the ISO is set up to 100, since increased ISO numbers will accept an impact on the guide number calculation.

Now let'due south wait at some examples.

When you lot're because a new flash buy, the only number that the manufacturer provides is the guide number - information technology's up to you to figure out the other two numbers in the equation.

The most obvious variable to consider offset is flash to subject distance.

If we presume that the discontinuity is set to a constant value of f/four, then it quickly becomes apparent that flashes with higher guide numbers can effectively light subjects that are farther away:

Guide Number	F-Stop	Flash to Subject Distance	Calculation
40	f/4	10 anxiety / three meters	GN = 10 ft. 10 f/4 = 40
80	f/iv	20 feet / half dozen meters	GN = xx ft. 10 f/4 = eighty
120	f/4	30 feet / ix.i meters	GN = 30 ft. x f/4 = 120
160	f/4	40 feet / 12.2 meters	GN = 40 ft. x f/4 = 160

Alternatively, if your flash to subject distance is a constant, and so flashes with college guide numbers permit you to utilize narrow lens apertures (which helps you achieve more than depth in the paradigm and keeps everything precipitous):

Guide Number	F-End	Flash to Subject Distance	Adding
xl	f/four	x feet / 3 meters	GN = 10 ft. 10 f/4 = xl
80	f/8	ten feet / 3 meters	GN = x ft. x f/8 = 80
110	f/eleven	ten feet / 3 meters	GN = 10 ft. x f/11 = 110
160	f/16	ten feet / 3 meters	GN = 10 ft. x f/xvi = 160

Then there you have it: you can leverage the extra power of a wink with a loftier guide number in one of two means:

1. Past using a wide aperture, yous can light subects that are farther away
2. Staying the same distance from your bailiwick, yous're able to use a wider range of apertures

Bottom line: expect for a flash with a high guide number if you think that you'll oftentimes use the flash to calorie-free subjects from a distance OR if yous don't desire your aperture choices to be limited every time you apply a flash.

Guide Number Reporting

If y'all go shopping for an electronic flash online, you'll probably encounter it listed similar this:

[Flash Proper noun] with Guide Number (GN) of 141 ft. / 43m

Sometimes the ISO value will be stated, only if it isn't just remember that all guide numbers are calculated at ISO 100.

The only value ever reported every bit the guide number is the flash to discipline distance in both feet and meters.

You'll note that the lens aperture used to calculate the guide number is left out of the reported value, which leads quite well into our adjacent topic.

Guide Numbers = Marketing Hype

We at present come to the only drawback of using flash guide numbers to evaluate and compare different electronic flash units.

Over fourth dimension, wink manufacturers take come to rely on guide numbers to sell flashes a lot similar camera manufacturers have relied on megapixels to sell cameras.

As such, they "optimize" the environments in which they test their flashes and so that they tin study a high guide number on the flash spec sheet.

Since you probably won't be using your flash to light subjects in a controlled environs, you'll observe that the "real" guide number of your wink doesn't match what the manufacturer states in their promotional literature.

So what's the takeaway hither?

Use guide numbers to go a general sense of the power of an electronic flash, but if you're trying to compare two about identical units, don't get too hung upwards on one with a slightly higher guide number.

Nevertheless, if you're looking at two unlike flashes and 1 reports a guide number of 72 while another has a guide number of 190, the one with 190 is clearly the more powerful wink (and hence much more expensive).

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Source: https://www.digital-slr-guide.com/flash-guide-number.html

Posted by: rodriguezwiterestich.blogspot.com

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