The Science of Exposure and Metering
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The Science of Exposure and Metering


This Filmmaker IQ Course is proudly sponsored
by Northeast Community College whose media arts program offers concentrations in Audio
Recording, Broadcasting and Digital Cinema. Hi, John Hess from Filmmaker IQ.com and in
this course we are going to take a deep dive, go far beyond the triangle and establish a
fundamental understanding of exposure and metering. Outside of promises of future recognition
in leiu of payment from shifty producers; Exposure is basically the amount of light
per unit area reaching a photographic film or electronic imaging sensor. This light is then translated by the photographic
medium into an image. If we have too little light for our photographic
medium, the image is said to be underexposed and the image looks very dark. If we have too much light, then the image
is Overexposed and looks too bright. So just like Goldilocks, we want our exposure
to be just right – for the sake of simplicity let’s just call this the optimum exposure
in that it renders a middle gray object as middle gray in our final image. Here in our simplified shot scenario with
three different shaded spheres, the optimum exposure should render the middle gray sphere
as middle gray in the final rendering. Now of course – for artistic reasons you may
not want middle gray to be in the middle – you may prefer to either over or under the optimum
exposure. But for the remainder of this lecture I will
be using the optimum exposure as our default when I say word “exposure”. So what are the concepts that govern the exposure? Well we are not the first nor the last ones
to approach this topic – it’s almost become like a past-time for filmmakers and photographers
to make and watch videos on this very subject. No doubt many of you watching right now probably
have a good understanding of exposure and are just tuning in just to judge how I present
the information. A lot of people will talk about the exposure
triangle. Heck, I’ve even made a graphic depicting
the triangle myself. But, I’ve always felt like something was
missing from that model. Instead I want to present to you a different
way of thinking. Remember all photography and by extension
all motion picture is really the record of light as it passes through a lens. So let’s think of exposure as the path that
light has to take. This path begins from the scene luminance,
through lens modification, the exposure as governed by aperture and shutter speed and
then finally onto a recording medium who’s sensitivity to light we can control. Let’s start at the very beginning, which
happens to be a very good place to start. Without light there can be no exposure – so
to start at the beginning means we start at the light source. We are going to get into some pretty heavy
terminology here – you don’t need to memorize the exact figures – but know that everything
from here on out is dependent on the lights in our scene. There are three terms we are interested in:
The intensity, the illuminance and the luminance. Let’s begin with the intensity. The luminous intensity over a given solid
angle is measured in something called candelas from the latin word for candle which is exactly
how this was originally measured. A typical candle will have an luminous intensity
of of 1 candela. But unlike radiant intensity which is all
radiant energy from a source, which is measured in watts per steradian, the Candela is a special
SI unit which is weighted toward the part of the electromagnetic spectrum that we can
actually see. In more precise definition: a candela is the
luminous intensity, in a given direction, of a source that emits monochromatic radiation
of frequency 540 x 10^12 hertz and that has a radiant intensity in that direction of 1/683
watt per steradian. You don’t need to be memorize that… the
fact is I didn’t… the point is: So while this candle is giving off infrared heat as
well as visible light the Candela is only a measuring the visual light it emits in a
direction. Candelas as we’ll see in a moment refer
to intensely bright something is. The light that flows from a light source is
called the luminous flux or illuminance. The total amount of luminous flux from a source
in all directions is measured in lumens. 1 lumen is amount of light emitted per second
in a steradian from one candela – a Steradian being the SI unit of solid angle. – basically its area of a surface of a sphere
which has the surface area equal to the radius squared There are 4 pi steradians in the surface of
a sphere – so a candle with the brightness of 1 candela is emitting 4 pi lumens or roughly
12 lumens. Now if we obscure half of the candle with
a non reflective surface – the candle is only giving off 6 lumens even though it still has
a luminous intensity of one candella. Lumens is something you will come across when
looking at lighting fixtures – they tell you how much total light is produced by the the
fixture and you will often see this when purchasing both consumer and professional lighting products. Now we come to the unit we use to measure
how much light actually flows through or lands on a given area in space: the lux. One lux is one lumen per square meter which
also happens to be the flow generated by a one- candela light source at the distance
of one meter (this is because of the definition of a steradian). The imperial version is the foot candle which
is 1 lumen per square foot which is also the amount of light of one candela at one foot. There are 10.76 foot candles in one lux so
a quick approximation between foot candles and lux can be made just by multiplying or
dividing by 10 How much lux we have is not only governed
by how many lumens is being put out by the light source but also how far the light source
is. This is governed by the inverse square law
that states the light intensity will fall off by the inverse of the square of the distance. In other words double the distance and you
reduce the illuminance to one quarter – triple the distance and reduce the illuminance to
one ninth. One small caveat, this law is really only
for isotropic radiating sources – that is lights emitted from a point in space – like
this candle.. When using lenses that alter the direction
of the light rays – the inverse square law still stays in effect, it’s just that the
effective point of origin moves further back. But this is a small caveat that doesn’t
really manifest itself in a noticeable way in practical application. I just bring it up as sometimes the math won’t
precisely work out unless you take this fact into consideration. But rarely are we photographing a light source,
Let’s talk about luminance, sometimes called brightness. Luminance refers to the light that is reflected
off an object in the scene and is measured in candela per square meter using SI units. The imperial unit is Foot Lamberts which 1
divided by pi candelas per square foot which is equivalent to 3.426 candela per square
meter. As you can imagine there are a lot of factors
that govern how light bounces off an object, from the intensity and distance of the light
to the viewing angle, the material reflectivity and absorption of the of material we are looking
at. There’s a lot of different factors at play. In the world of luminance displays with monitors
and televisions, you’ll sometimes here the non-standard unit “nit” which is equal
to 1 candela per square meter. I’m sure we’ll get back into all these
units in a course on lighting but I do want to introduce these terms because you will
see them over and over again as you begin to work with exposures and metering. So let’s just recap briefly. The intensity of a light, the visible radiant
energy is measured in candelas. 1 candle traditionally is one candela. The luminous flux generated by this light
is measured in lumens which is the flux from one candela per steradian. In terms of illuminance, the amount of light
flowing through a given area is measured in Lux which is one lumen per square meter or
foot candles which is one lumen per square foot. The brightness of light as it bounces off
an object in a scene or luminance is measured in candela per square meter or foot lamberts
which are 1 divided by pi candelas per square foot or 3.426 candela per square meter Got all that? I know it’s a lot but we’ll see them pop
up again and again as we get into metering so you might as well be familiar with them
now This part of the pathway of light, the scene
illumination and luminance, is the only part of the exposure process where we can actually
actively add light. As such this part is crucial for determining
the exposure. From here on out we are essentially budgeting
or cutting down how much light will eventually make it to our sensor. There are essentially two kinds of lens modifications
that can alter our exposure and although their exact placement can either be in front of
the lens or behind the lens itself, I have decided to place it second for the purposes
of discussion. The first possible obstacle in the pathway
of light are filters particularly Neutral Density or ND filters. The function of ND filters is to reduce the
amount of all light entering the exposure equation which we’ll get to in a second. Think of ND filters as sunglasses for your
camera. ND filters are rated for how much light is
cut in powers of 2 called stops – this is a term you will hear over and over again in
this video. One stop of light loss means that only half
of the original light will make it through – two stops means only a quarter and three
stops means only one eighth of the light. Sometimes this written as a number using the
optical density equation which I won’t get into here. Basically 0.3 is one stop and each 0.3 is
one stop more. If you see a 1.2 ND filter that means it’s
cutting the light by 4 stops – that’s 1/16 of the original light. The other kind of lens modification that affect
the exposure are Teleconverters and Telecompressors. A Teleconverter takes the incoming image and
blows it up – the effect is increasing the focal length of the lens but it also reduces
the amount of light because we’re basically throwing away the edge of the image as we
zoom in. For example this 2x lens extender doubles
the effective focal length of the lens but reduces the exposure by 2 stops – meaning
only a quarter of the light will get to the sensor. The opposite of an teleconverter is the telecompressor
like the popular metabones speedbooster. Instead of blowing up the image, it compresses
down the size of the image circle laid down by the lens to fit a smaller sensor than what
the lens was designed for. Because less light is wasted on non-exposing
elements of the camera, the effect is an increase of exposure – though light is not being added,
it is only be more concentrated on the sensor itself. For example this 0.71 speed booster reduces
the focal length by a factor of about 1 divided by square root 2 – which results in a gain
of 1 stop of light. Though the calculations we will make further
down this course do not generally consider these lens modification factors – you have
to keep them in mind when you are trying to determine your exposure. Now let’s talk about the actual act of exposure. Exposure has two parts – how much light we
let in from the scene and how long do we let the light in for. How much light we let in is governed by the
aperture – the aperture is described by the f-stop. We cover this a little more extensively in
our properties of Lenses video but let’s remind ourselves that the f-stop is equal
to the focal length divided by the diameter of the entrance pupil or effective aperture
as measured from the front of the lens. So the lower the f-stop on the lens, the bigger
the entrance pupil is – the more of the available light we are letting in to our camera. How much time we let the light in for is governed
by our shutter speed. Shutter speed in photography is described
in fractions of a second or even seconds or minutes for really long exposures. In motion picture cameras sometimes they are
described as degrees – A shutter on a motion picture film camera is circular, the degrees
represents how much of the shutter is left open to expose the film. When using degrees for the shutter speed,
we must consider the frame rate to determine the shutter speed in fractions of a second. If our frame rate is 24 frames per second,
a 180 degree shutter will give us an effective 1/48th second shutter speed. If our frame rate is 30 frames a second and
we have that same 180 degree shutter – then we have an effective shutter speed of 1/60th
of a second. I know some of you are chomping at the bit
just waiting for me to demonstrate what different apertures and shutter speeds look like. Well hold on, because there’s one concept
that I want to discuss which will tie these two things together: The Exposure Value System
or EVS. The EVS concept was developed by the German
shutter manufacturer Friedrich Deckel in the 1950s. The idea was to replace the two numbers – the
f-stop and the shutter speed – with just one number – the EV. The math looks a little intimidating but it
really is quite simple once your examine it: Ev equals log 2 of the f/stop squared divided
by the exposure time in seconds. Let’s work this out: The Log 2 just means
that each step of one on the EV scale, doubles the amount of light. So an EV of 10 is double the amount of EV
of 9 – each 1 EV is one stop. Now going into the equation itself – the reason
why aperture is squared is because if we want to add or subtract a stop of light using the
aperture we have to multiply or divide the f/stop by the square root of 2. By squaring it the f/stop value, each stop
is now a multiple of 2 – which gives us the even steps once we take a log base 2 of the
number. Here is a common EV chart. Let’s pick EV 12. Along the sidewe see a list of possible f
stop values. If we want an exposure value of EV 12, shooting
at f/1.4 shows that we need a 1/2000th second exposure. Shooting at f/2.8 we would need a 1/500th. Shooting at f/4 we would need 1/250th of a
second. And going all the way up to f/11, we would
need a 1/30th of a second exposure Regardless of what combination of shutter speed and aperture
we use – so long as we are at EV12 the exposure is identical. And here’s the real world proof with this
lighting model demonstration. The image on the left is shot at F/11 with
a shutter speed of 1/30th of a second. The image on the right is shot at F1.4 at
1/2000th of a second. Same exact exposure, but different effects. With the wider aperture on the right we have
a shallower depth of field evident in the bloom of the stars in the background. But the higher shutter speed freezes the motion
on the spinning checked wheel which is only a blur in the image on the left. We can even animate the transition between
these two extremes – here each frame of the transition is a move of 1/3rd stop in shutter
speed while moving in the opposite direction with the aperture. The exposure does not change – this direct
relationship between the shutter speed and the aperture as part of the exposure is called
reciprocity. One stop gain in shutter speed is exactly
the same in terms of exposure as one stop gain in aperture – but as you can clearly
see, the effect of changing one or the other has very different visual consequences. At this stage of the light path we have determined
how much light is actually inside our camera. Now the last bit is the sensitivity of the
recording medium itself. Now we get to the final stage of the pathway
of light – where it is finally recorded on a medium. Historically there have been a lot of different
systems for determining how sensitive a recording medium is – that is how much or how little
light is needed to create an exposure. I’m only going to focus on the most modern
one – The ISO standard that has been in place since 1974. Determining the speed of a piece of film is
pretty complicated and would probably take up full course video just trying to explain. The most important thing to remember is that
unlike f/stop or EV, which are logarithmic scales – the ISO is an arithmetic scale. That is in order to double the sensitivity
of the film you double the ISO number. So ISO 200 is twice as sensitive to light
or one stop more sensitive to light than ISO 100. ISO 400 is twice as sensitive as 200, ISO
800 is one more stop sensitive than 400 and so on. In the celluloid film world this sensitivity
to light had to do with the size of the silver halide grains in the emulsion. The bigger the grains the less light needed
to make an exposure. The downside to this is the image was grainier. The finer the grain, the more light was needed
to make the image but the advantage was very clean images. When we talk about exposure for digital – there
is a similar effect but the cause is significantly different. When a digital camera makes an exposure each
individual pixel on a camera sensor responds with a voltage – we go through the process
of how digital sensors work much deeper in this previous video. But the voltage generated by the exposure
is very very small. We need to amplify the voltage before we can
send it to an analog to digital converter. The amount of amplification is what the ISO
on a digital camera controls. Now imagine the volume knob on your favorite
stereo – the more you turn up the volume the louder the music but also the background noise. Raising the ISO not only raises the signal
from an exposure, it raises the noise floor as well which is why higher ISO images have
more noise. Although shooting Camera RAW formats does
give you back some control over the ISO, the amplification occurs before the electric signal
from the sensor is sent out to analog to digital converter and recorded as RAW. Now the details may differ from camera to
camera – but you still need to get the ISO in the correct neighborhood even if you’re
shooting RAW. There are some strategies for ISO use when
working with RAW and Log files which we’ll get into in a future course on dynamic range. A couple of caveats worth mentioning before
we leave this section on ISO. The ISO standard organization gives camera
manufacturers a choice of 5 different techniques for determining the ISO settings on their
digital cameras so that they would match the ISO performance of film. This does occasionally lead to mismatch of
ISO rating on the camera to what the actual ISO performance of the sensor itself – but
that’s a rabbit hole for another time. We just breezed through all the elements of
the light path for exposure. Now let’s put it all back together again. First let’s talk about determining the exposure
from a luminance perspective – that is from the camera’s perspective taking in the light
that is coming from this scene – this is also known as spot metering. Here is the exposure equation: N squared divided
by t equals L times S divided by K where N is the f/stop, t is the shutter speed, L is
the average scene luminance in candelas per meter squared, S is the ISO value and K is
the meter calibration constant – Canon, Nikon and Sekonic use 12.5 but this value can range
from 10.6 to 13.4. If you recognize the left side of the equation
there – it’s because we saw it earlier in our discussion on Exposure Value (EV). So this equation can be rewritten as EV equals
log base 2 of L times S divided by K. Don’t get too hung up on the math… because
you really never ever really do it yourself – either your camera or your light meter does
it for you. I’m just walking through the math to show
you what’s happening inside these devices. So let’s take out our light meter and put
it in spot meter mode. This is a reflective light mode which is how
we determine luminance. The spot meter only determines the light coming
from a small portion of the scene – this particular spot meter evaluates a 5 degrees portion of
the scene. I have the meter set to just give me a raw
data of candelas per meter squared. In this scene I’m aiming my spot meter at
the two gray figures sitting on the film reel. When I take a reading it reads 24 cd/m2 – now
this is going to be essentially an average of 5 degrees around those two figurines which
will give a pretty good sense of the average scene luminance. Now it’s really a matter of plugging in
different desired settings for the three camera side variables. Let’s say I know I want to shoot with ISO
1600… plugging in the numbers I see I get and EV of 11.5 Now maybe I know I want a shutter
speed of 1/48th because I’m following the 180 degree shutter rule. So plugging those numbers in I get that I
need to shooting around f/8. But let’s say I look at the image and I
think maybe I want a shallower depth of field and let those stars in background stars bloom. Let’s say I want to go down five stops to
f/1.4. Looking back to our pathway of light there
are 4 other factors we can adjust to bring back our exposure. First, we can decrease the amount of light
in our scene perhaps by using a dimmer, by putting filters on the light, or by moving
the light the further away from the subject. But the problem with this is it changes our
lighting ratio between the background stars and the foreground. And let’s just say I want to keep the lighting
just the way it is so I don’t want to touch it. Now I could change the shutter speed down
five stops going down from 1/48th a second to 1/2000th of a second… but that looks
kinda funky. So let’s leave it at 1/48th. There are two other things we can change. This camera has built in ND filters rated
for 2 stops, 4 stops and 6 stops. Let’s engage the 4 stop ND filter, now we’re
getting warming. We just have to go down one additional stop. So what’s left is the ISO. I can go from ISO 1600 down an entire stop
to ISO 800 and now the image is back to the same exposure only this time with a much more
shallower depth of field. When we perform a spot meter reading – we
are looking at a particular part of the scene which we want to be exposed to middle gray. But what if we don’t have anything to reference
that has the same tonality as middle gray? This is where you can turn to the Zone System
created by Ansel Adams and Fred Archer. We won’t spend too much time talking about
the Zone System other than to give you a general jist of the idea. The Zone System takes the full dynamic range
from darkest to brightest and breaks them out into 10 zones. The middle zone, zone V is where your middle
gray is – a move of one zone in either direction is a shift of 1 stop. Then Adams assigned different everyday photographic
items to different zones. So the middle zone, zone V would be where
clear northern sky, dark skin, or average weathered wood ought to sit. So if you take a meter reading of these things
– the value that your light meter gives is the ideal setting you want to use. Now one stop above, Zone VI would include
average caucasian skin, light stone or shadows on snow in sunlit landscapes. If you took a spot reading on one of these
items your meter would give you settings that are 1 stop above the proper exposure. Since you know it’s zone VI you know to
set your camera one stop lower to get the right exposure. The Zone System goes pretty deep beyond what
I’ve described and each zone has a list of commonly found photographic elements that
you can reference. There is some criticism to the zone system
but it is one practical way of determining your exposure – if you use a monitor with
false color options, that’s almost a modern version of the zone system. However modern digital cameras offer a variety
of other more precise methods of metering that include things like center weighted average
metering or matrix metering use the equation that I outlined earlier. Basically these things are determining the
exposure settings by taking several different spot readings on the sensor and calculating
the average scene lumination to be plugged into the equation. So far we have been determining the exposure
from the scene luminance – now let’s look at it from the illuminance side – that is
judging the exposure based on the lights in the scene. For this we turn our light meter into an incidence
meter. Instead of candelas per square meter we now
measure in lux. When we take a reading we are asking how many
lux – that is lumens per square meter – are passing through this point in space. The equation is just slightly different. We replace L with E for illuminance and the
reflected light meter constant, K gets replaced with the incident light meter constant C where
C is between 240 to 400; a value of 250 is commonly used. And then the math works out pretty much the
same way. The reciprocity rules stay in effect exactly
the same way as it did with the spot metering exercise and you don’t have to do the math
at all because it’s all done inside your meter. So why would you use incidence metering over
spot metering? Well there are several advantages. Using incident metering is you are measuring
how much light is falling on the subject, regardless the reflectivity of the subject
in question – if you took a spot reading of a black and white rabbit, my buddy Axel here,
you’d get different readings for the black and white patches – but an incident reading
would give you a more consistent answer because it is measure how much light is falling on
him. Spot meters can also be thrown off by colors
– here are three different colored spheres – each one with a slightly different spot
reading – even though the lighting remains even on all three spheres. Furthermore incident readings are useful to
determine lighting ratios and judging the power of one light to another light – we’ll
cover this concept in greater detail in a future video. But incident readings aren’t always practically
especially if you can’t get to the subject that you’re photographing in order to take
an incident reading – say like El Capitan in this photo by Ansel Adams. In situations like that you have to use a
spot meter – although today our digital cameras already have a spot meters built in. From Candelas to EVs, I hope what we covered
here has taken some of the mystery out of exposure and given you a more complete understanding
of how light and metering works. Now although we are using precise numbers,
ultimately exposure is about producing art – you can over expose or under expose to your
taste the meter is just there to give you more information to base your creative decisions. From Scene illumination, lens modification,
exposure and sensor sensitivity – each of these aspects of the path way of light are
crucial to creating the final image – ultimately it all boils down to one relatively simple
equation. When we say photography is all about light
– we aren’t kidding. Light is all there is whether you are carefully
crafting it or snapping a selfie. This interplay of light that we’ve discussing
is happening in every photograph and every frame of motion picture. Hopefully all of this will help you take the
next step in your photographic and cinematic journey. All that’s left is to go out there and expose
something great. If you liked this video give it a thumbs up
and subscribe – hit that little bell icon if you haven’t already – and do us a favor
and share this video. Follow us on Twitter and Facebook and consider
becoming a patron on Patreon to help us bring you more content like this as well as access
to our Patron only content. Link to our full course on FilmmakerIQ.com
in the description below. My name is John Hess, and I’ll see you at
Filmmaker IQ.com

100 thoughts on “The Science of Exposure and Metering

  1. 1/3 of the way in this is already the most comprehensive explanation of the terms used for photon emissions…. lol

  2. want to ask about cinematography , it's will be cool if you make episode about it and explain it in your way , thank you

  3. https://youtu.be/-BHbY9p4BgI?t=427
    I thought that 1 foot candle equals 10.67 lux, not the other way around. Am I missing something here?

  4. isn't the f-number of a camera lens calcualted from the diameter of the entrance pupil and not as measured from the front of the lens?

  5. Another great video! I didn't know they'd changed the definition of the candela from black-body to monochromatic, thanks for informing us.

  6. I only have one word for this video which is the first ever I watched out of the channel as seen on FStoppers and that word is G R E A T ! ! ! Thank you so much, you present it all in a very simple way which adds to the already great content.

    GRAZIE

  7. It blows my mind how, in America at least, we still teach math classes on such a baseless conceptual level when I can watch a video on photographic exposure and understand the maths perfectly with respect to its function.

  8. I just watched all your episodes and now I am searching whole internet to find quality content about filmmaking just like yours 😀

  9. I am one of those who watched a lot of videos on exposure (and cinema and video related stuff) and yours is more complete, deeper, precise and comprehensive than the average as always. Thank you for you work. It's gold!

  10. May I ask what program you use to make these videos? It's so comfortable to watch… I am totally new to photography, I don't even know how to use my camera yet but this video was great Information! Although I am not (yet) into photography and filmmaking I subscribed!

  11. 1- Why are we watching this if we already know it?
    Cause you are awesome and deserve views. 🙂

    2- The Exposure Triangle
    The exposure triangle explanation isn't perfect but it's a good starting point for explaining to someone who doesn't understand exposure at all.

    Why are my pictures blurry?
    Why are my pictures all grainy?
    Why is my picture so dark?

    All of those can be answered with the basic explanation of the exposure triangle.

  12. So….. THAT'S what EV on my camera stands for! So much to consider while taking a shot, but so little time!

  13. These videos are so great. I mean I could say a bunch of really hyperbolic things, but they're just really wonderfully interesting and high quality learning material.

  14. Holy Hell I love this!! Stumbled onto this channel completely by accident and now I can't get enough of the nerdiness… yum!

  15. I feel like I've learned almost everything about exposure thanks yours video. The most scientific channel on YouTube which is about Filmmaking

  16. long, extremely detailed, mathematical equations. I loved it! exactly what I needed. thank you! don't change, you're a asset to youtube.

  17. I don’t get why these videos get so little views in relation to subscribers….they are very well done and articulate, makes the majority of the info easily digestible. Hey, John Hess. Why haven’t you pitched a history of film show to any tv studios? This would be perfect for the history channel or something similar….keep up the great work, you’ve gained a loyal subscriber.

  18. Es tan agradable el ver estos videos, puedo dejar todo de lado sólo para escuchar y ver esta clase magistral, gracias por compartir

  19. WOW, I never understood all the science behind Exposure until I watched your video. You have an amazing way of breaking it down and using excellent graphics images to be able to understand the material. You Rock! Thank you for putting this information out there.

  20. Let's start at the very beginning, a very good place to start. When you read you.. Ah yes; now I've got that song in my head.

  21. Amazing information man. Please keep uploading videos, you deserve a much bigger audience than what you have!

  22. As a Producer who is learning to become more a Director of Photography – lighting has always been one of those skills I just haven't nailed down, especially when talking to more experienced tech-centric DP's. This definitely helps make those connections to make the art-to-science translation.

  23. sometimes people tends to forget that photography literally means graphy of photons.

    even some people gets angry when you call a photograph picture, they say photographs are not pictures (:
    fortunately they are so wrong, a photograph is a "type of picture" which uses photons as paint, lens as brush and camera (its sensor) as canvas.

  24. Wonderful and informative video, but I have a question…

    As a photographer, I'm well aware that raw image files come from raw sensor data after minimal processing (ISO amplification, noise reduction, analog to digital conversion, etc.) but I'm curious and still confused when it comes to raw video and where ISO comes into play. In raw images, ISO amplification is applied BEFORE the raw image file is made which means you truly can't change ISO in post (it's set when you take the photo). However, I've heard/seen from some videos and articles that raw video is raw sensor data and that's it (with no ISO amplification meaning you CAN change this in post. For example, this website at bottom of paragraph 3, basically says you can change ISO in post: https://www.hdvideopro.com/workflow/capture-workflow/formats-explained/). But you mention at 21:29 however that ISO amplification occurs before it is made into raw video. So which is it? What exactly is "raw video"? Is it raw sensor data or is it the video equivalent of what a raw image file is after ISO amplification? If it depends, does it depend on the camera and its capabilities? Maybe I'm missing something…

    If anyone knows this, I'd greatly appreciate it if you replied back!

  25. As a guy who is finally making some photos that I can live with, I am trying to dip my toe in video. 180 degree shutter seemed like just another random piece of terminology to remember (as random as f/stop), thank you for explaining why the term is used. With how video is exposed it makes total sense. The rest of the video is great too, but this feels like it has taken a load off my mind 🙂

  26. why is not there a electronic variable nd filter (such as the aputure dec vari-nd) in all camera that records video ? this is a lcd technology that does not cost much, why is it not in all video recording devices ?

  27. Very well done as always. I learned a long time ago that the most important tool for a photographer, next to the camera itself, is a good light meter. You can ensure the scene is ideal before the camera even arrives.

  28. What an excellent channel and series of well-presented content. I am wondering, though—and I thought you were going to touch on this while discussing ISO—if, when using digital cameras in particular, whether we should keep in mind the native ISO when adjusting for correct exposure? Many cameras, even lower-end pro cameras, like the Canon EOS cine offerings, can start to yield sketchy (noisy) images when ranging too far afield of the native ISO. Also, may indy filmmakers are using DSLRs, which greatly suffer outside of native ISO.

  29. What aspects would ypu like to corrwct if you want to show the right shoulder side shirt colour a little dull to match up the tone of the shirt in the remaining part ???

  30. John, according to the wikipedia definitions, 1 cd = 1 lm/sr. Likewise, 1lm = 1 cd x sr. The way you made it sound, that lumens are the number of candelas per steradian, I would gather you mean 1 lm = 1 cd/sr.

  31. When i hear hi, i'm John Hess, i'm opening my notebook and ready for lesson, thank you so much this is my fav class

  32. These kind of deep dives are exactly what I’m looking for. Got driven here by the new dual iso video you posted. Can’t wait to catch back up to that vid. Thanks!!

  33. “Optimal” exposure is when the recording medium can reproduce both the highlight and shadow detail on print or screen as perceived by eye. When viewing Half Dome in person from a distance our eyes will adjust to expose the brightest highlights correctly for detail at the expense of perceiving the shadow detail. The “genius” of Adams photography was that his prints render the full range detail the eye would only see after wandering into the darker areas and having time to adjust; they reproduce more than the eye can see in many situations. He also manipulated perception of the scene by using red filters at capture to darken skies, increasing the overall contrast in the print, also making it easier for the eyes of the viewer of the print to see highlight and shadow detail simultaneously.

    I learned his Zone System in 1971 from his books using a Nikon F 35mm roll film camera and a Honeywell 1° spot meter purchased so I could directly measure shadows, highlights and scene EV range and not need to interpolate everything from the middle gray 18% Kodak Gray card reference. In the zone system the ISO value used on the meter is adjusted based on testing to find what actual ISO will produce the needed shadow density on the neg. to reproduce it on the print. The highlights are then “dialed in” to the range of #2 print paper by testing varying development times until the baseline cross-lit sunny face in dark and light clothing fits the range of the #2 print paper as seen by eye and looks real.

    Adams learned back in 1920 with orthochromatic film which could be developed under red safelights by eye. Old timers would pull the neg out of the developer when they saw the highlight densities reach the point they knew would fit the range of the paper; expose for the shadows / develop for the highlights. Adams standardized the process by finding the exposure and development needed to fit a “normal” cross-lit sunny outdoor scene to the range of a #2 print paper grade using the tools available at the time: a Weston reflection meter and 18% gray card its reading were calibrated to reproduce accurately on the print. But the first test in the system was to adjust the calibration point for the meter to ensure the exposure measured off the card put the required density and detail in the shadows on the print. If the nominal IS0 of the film being used didn’t correctly expose the shadows in the first test the ISO setting of the meter was adjusted until it did. Then different negative development times were tried until the prints exposed for optimal shadow rendering “as seen by eye (after eyes adjusted)” also had the similar optimal highlight detail. Additional testing was done on overcast days of lower contrast or beach and snowscapes with higher contrast to determine how to adjust neg. development time with the same definition of “optimal” exposure: rendering the full range of detail as seen by eye. Once that was accomplished Adams would make a full range evaluation print on #2 paper then artistically decide how to manipulate the total values in the photo selectively with dodging and burning, making notes on a tissue overlay a darkroom assistant could follow to crank out prints for sale while he was back out in the field capturing more images.

    With a spot meter I was able to directly measure the EV range between shadow and highlight used to establish the “Fits #2 paper” baseline from the testing and know if the EV wasn’t the baseline 10 stop range I would need to adjust paper contrast with filtration when printing to render range on the print optimally — as perceive by eye. With that direct measurement there was no need for all the Zone V nonsense: just capture the scene so the full range would fit the range of the print, then dodge and burn as need to interpret what the camera captured “artistically”. Instead of varying development times for scenes of other than normal contrast I change the contrast of the polycontrast print paper via magenta/yellow filtration. From systematic testing I determined what filter pack was needed in the colorhead of my enlarger to fit any scene range from EV8 to EV12 to the paper rendering the full range of tone and detail.

    My first job out of college was assisting Monte Zucker, the top wedding photographer of the day who used color negative film / prints. The problem with color prints was they could not reproduce the full range of tone from white dress to black suit with the single flash methods being used. Zucker, from his training in studio lighting with Joe Zeltsman understood the solution to that problem was to change the scene contrast by using two flashes in a key over neutral fill arrangement. The fill light on a bracket over the camera took care of exposing the shadows for detail. But adjusting exposure for the shadow detail in the black suit rendered the white dress of the bride middle gray. The highlights on the dress over that foundation where created with a second flash positioned 45° to the side and 45° above — the same angle of the sun at 10:00 and 2:00 with power adjusted via relative distance to subject until the full range of tone with natural looking 45° lighting was rendered on the print giving them realism not previously seen in “run and gun” flash photography. When shooting from 11’ the off camera flash was put at 8’ making it 2x brighter per the inverse-square law which turned out to be the lighting ratio needed to fit the full range of the flash illuminated cross-lit scene to the range of the color print paper.

    What I quickly realize was that the goal of reproducing detail as seen by eye on the print was the same as with Adams B&W system but the more limited range of color print paper required the use of flash to change the range of the scene via control of the lighting ratio of key overlapping even fill. The new tools that made it possible in the late 1960s – early 1970s were the new battery operated Graflex Electric flash units (single power with huge 410V batteries) and Wein photocell trigger for the off camera flash.

    With digital photography the goal is the same — fitting scene range to sensor to render it “as seen by eye” to the extent possible. The viewer of a photo or video will not notice or care if the midtones are exposed correctly but they will notice if highlights and shadows are not rendered “normally” based on in-person perception of similar scenes. So again the “optimal” exposure is the one that will render the full range of detail in the scene with the detail in the highlights of most usually being the most critical and deemed “fake” when not rendered corrrectly. My first digital camera in 2000 was a Kodak D290, a 3x zoom camera which was the only “point and shoot” at the time with a PC sync connector for flash. I discovered the same dual flash method and lighting ratio method I’d learned shooting weddings in 70s on color negative film worked to fit full scene range to sensor, screen and prints. Many pro photographers starting using the Kodak D290 for test shots instead of Polaroids.

    Sensors and image processing methods have evolved in the years since that a full range of tone can be rendered “as seen by eye” without the need for artificial. Nowadays all one needs to do is keep the highlights below clipping via the warning in the playback so as not to blow the highlights and have a reasonable expectation that the shadows will also be rendered with detail.

  34. You’re the best man. It’s great to find explanations that are both in depth technical AND practical in terms of usage.

  35. This is like actually being in class. Watching other YouTubers, they may tell you what works for them but never give you a detailed why. This answers those questions to understand the concept behind WHY exposure works the way it does. I love it, I'm subbed and delving into more of your videos!

  36. So much great info! I really love the channel and subbed but PLEASE stop with the slow zoom in when you are talking. I feel like you are leaning into my face when you're talking to me. its not natural, if someone were to do that to me while i'm talking to them face to face I'd ask them to take a step back. I know i'm prob the only one bothered by this so apologies if it seems like im nit picking…and maybe I am. You're videos are really great but that just stands out to me really bad.

    Again, great channel!

  37. I went to film school. The most advanced course I took (which wasn't necessarily the most advanced course they offered) doesn't even come close to this video. DON'T GO TO FILM SCHOOL PEOPLE!

  38. Protect the highlights .especially when shooting on digital ,actually i like when shadows are a bit darker but when highlights are overexposed it's very ugly especialy on digital!

  39. Hi, thank you for your informative and well presented videos. There is one thing about exposure that is not clear to me and it is something I have researched a lot and still do not have a clear understanding of. In one of Tony Northups videos, he asserts that when using a Lens on a crop sensor camera, you must not only adjust the stated Aperture f stop number by the crop factor to indicate true equivalence with a full frame (FF) sensor for DOF (I get this, several people have explained this well, I think including yourself), but he also states that the crop factor adjustment must also be made for exposure. i.e.A lens with a stated F stop of 2.0, when used on a m4/3 crop sensor camera, must be treated as an effective F 4.0 for exposure purposes. Is this because two sensors of 24mp, one being FF and the other being m4/3, that the m4/3 sensor must have smaller pixel points (same mp amount in less area) and hence is less light sensitive? Or, is there another reason for Tony making this claim. He freely admits that sensitivity of sensor is uniform across the entire surface of a sensor and that a photon falling on any part of the sensor will be measured the same. Some others have claimed that because a crop sensor only takes a cropped portion of the total light transmitted by a lens (e.g excess light is wasted outside the crop sensor area) this is the reason. Some make the point this is wrong because exposure happens at the Pixel level, not the total area. I don't believe Tony is argueing this as he admits that Total area is not what determines sensor sensitivity.

    I have never found a satisfactory explanation of this. I do not believe Tony Northrup is a fool or that he would deliberately misinform. The bottom line – Is the effective f-stop of a lens changed when using with a crop sensor camera and why? And if so, does this also apply to lenses specifically designed for crop sensor cameras?

    I hope you can reslove this question for me or, if you already have a video which addresses this question directly, please share the link.

  40. You sir are the best filmmaking resource on YouTube. You deserve some kind of award. This is a serious education you’re providing so many of us. Thank you.

  41. I’m going to need to watch this a few times to digest everything. I’ll need a notepad as well lol.

  42. i'm so glad i found this video. i've watched a dozen others that repeat the same basic info over and over and leave out key details as though they are some secrets of photography purposely kept hidden. this was incredibly helpful. thank you!!!

  43. Excellent content, but I have a question: what is the exact relationship between the stops of the zone system and the IRE scale of false colors? At 28:27 I noticed that the "zones" are not evenly distribuited accross the IRE scale. I know it's about the gamma curve and the contrast applied on the final grade, but I'm a bit confused on that. I think that understanding this would be very useful in analysing cinematography.

  44. @0:15 – Proudly Sponsored by Northeast Community College
    @0:25 – Intro
    @0:39 – What is Exposure?
    @3:24 – The Light in the Scene
    a. @4:01 – Intensity
    b. @5:16 – Illuminance
    c. @6:29 – Lux
    d. @7:27 – Inverse Square Law
    e. @8:26 – Luminance
    f. @9:31 – Recap
    @10:55 – Lens Modification
    @13:53 – The Exposure
    a. @15:47 – Exposure Value System (EVS)
    @19:03 – The Sensitivity
    @22:33 – Putting it all together and Spot Metering
    @26:30 – The Zone System
    @28:58 – Incidence Metering
    @31:21 – Closing

  45. I have a new short film and i had some issues with exposure. Even with ND filters, the skin tones appeared very dark. i ended up going with blown out areas to focus on skin tone. Any advice for the next film? I realize could've used diffusers to cut light down but it was a one day competition. https://youtu.be/3BWxNTn6Jqo

  46. Them: So… what do you want to do as an adult?
    Me: Filmmaking.
    Them: Why?
    Me: Because I like movies… and I'm bad at math, and in filmmaking I don't need them.
    John P. Hess: I'm gonna shatter this guy's dreams…

  47. This is valuable, 100% free information guys. People pay good money for this stuff. And here it is…a mountain of knowledge, literally at our fingertips. What a time to be alive!

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