Today i'm going to talk about the inverse square law and how in
understanding it will help you and your flash photography
the inverse square law sounds very geeky and scientific and most people will switch off
when it comes to things like this but it is quite a simple part of how light works
and it's essential to understand it to be able to get the result you want
from your flash photography the inverse square law states that the specified physical quantity
and in photography that's in the case of light is inversely proportional to the square of the
distance from the source so in layman's terms as you move your light source away from your subject
it gets diluted and more than you might think if you have your flash one meter from your subject
you get good settings for the flash at quarter power if you move the flash away by one meter
so the overall distance has doubled to two meters from the light source to the subject you'll have
to increase the flash by two stops to get the same exposure basically the same amount of light will
be covering four times the amount of surface as you double the distance so it will give you
quarter of the power of the intensity every time you double that distance another way to look at
it is if you were to change your settings and leave your flash power at one quarter power you
would have to increase the amount of light getting into your camera by two stops so from f8 to f4 or
iso 100 to iso 400 and remember as your settings double or half every time you change by one stop
changing by two stops will change the amount of light by a factor of four so in the example
i have given changing from f8 to f4 is two stops of light so this will double the amount of light
coming into your camera twice f8 to f 5.6 will double it once and from f 5.6 to f4 we'll double
it once again so you will end up with four times the amount of light being let into your camera
i've doubled the distance of the flash to the subject from one meter to two meters and to
compensate for this i've opened up the aperture from f8 to f4 in photography it's all about
distance from your light source to your subject and from your light source to your background once
you know about the inverse square law there are three ways you can use this to your advantage to
get the photo that you want now i'm only using one light at the moment to keep things simple i will
go into multiple lighting scenarios in a later video in this series but for now one light will do
let's say you're doing a headshot you might want to either lighten the background or darken
the background so once you've worked out the distance from the light source to your subject
if you keep this the same and then increase or decrease the distance to the background
you can change how that background looks so you're shooting a portrait and your subject is
right next to your background the light from your flash will bounce off that background
and come back into the camera now if you keep the distance from your light source
to your subject the same but then increase the distance between your subject and the background
that light will disperse and not be as intense on the background so again we'll look at them side
by side and you can see the difference with the background everything has been kept the
same apart from the distance between me which is the subject in this case and the wall behind me
which is the background so by placing your camera your light and your subject
further away or closer to that background you can determine the brightness of that background
when your flash is closer to your subject it'll be more intense and you will have to adjust your
settings to let less light into your camera in this shot i had the flash about 50 centimeters
from me the right side of my face is really bright and the left side falls into the shadows really
quickly if you look at the reflections of the light source in my eyes it's quite big this is
called the catch light also the background is darker as the light is so close to me if i keep
the distance from me to the background the same but increase the distance from me to the flash
to 2.5 meters to keep the same exposure on my face i have to increase the flash power to one quarter
and open up my aperture to f4 now you can see the light is more even on my face and the shadows
aren't as dark also the catch lights in my eyes are a lot smaller and the background is brighter
so again looking at them side by side you can really see the difference moving the flash away
from the subject or closer to the subject really can change how your photograph looks so let's say
for example you have someone with quite shiny skin you can move that soft box further away from them
to give a more even coverage whereas if you want to give a more three-dimensional look or you want
to brighten up part of the face you can move that soft box closer so this is where you need to get
the balance in getting the right size softbox and placing it at the right distance from your subject
now this just comes down to experience all you need to do is start taking some test shots get
your light get the softbox on the light and then fire off a load of different shots with that flash
a little bit further away and a little bit closer to see which one you or the subject likes best
the worst thing you can do is light a group of people only to have the people closest to the
light really bright and the ones further away really dark i do have to admit i've done this
a couple of times a long time ago and i had to do a lot of work in photoshop and lightroom to
even out the shot to make it look okay now during these times of social distancing i had to set up a
virtual group shot when the flash is closed to the group and placed to one side it's really easy to
get uneven lighting across the whole group in this example mike to the right is almost overexposed
whereas mic to the left is a little bit under exposed to fix this problem just move the light
away from the group and change your settings to suit then you'll get a more evenly lit group shot
also in moving it away the shadows will normally fall in better places especially if you're using
two or more lights in the first example the light was around about one meter away from me to the
right of the camera whereas in the second example i moved it back to about three meters away from
me and then change those settings to suit you do need to be careful about how far you move it away
but in making small adjustments in the distance of your light placement to the subject or subjects
you can really change how the light falls on them so in knowing about the inverse square law and
how the light falls off from your flash you can use this to your advantage to get the outcome
that you want in your photos now let me know your experiences with flash photography in the comments
below it'll be great to hear from you and also if you have any problems with flash photography
i might be able to address them in future tutorials so let me know about those in the
comments as well and if you want to learn more about photography click on this one next or to
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