Great BEF Question

Great BEF Question

Great Question:
In your announcement at the beginning of the week you mentioned to reach out to you if we were having trouble understanding BEF.  I have tried going over it so many times in my head but I just can’t seem to understand.  Could you help me please?


Let’s get you squared away now. 🙂 I am happy to help. Go get your camera so that you can dial in the settings as you read if you like. Take each part in stages. Understand each stage before moving on. Email me for questions.

We are going to start by going over a few things that you probably know but will assure we are on the same page.

As you know, your camera allows you to control how much light is going into it by controlling the ISO, shutter speed, and aperture. The ISO determines how sensitive your camera is to light. The lower the ISO the brighter your light should be. This means ISO 100 is good for bright light like full sun. When you are shooting inside, you will want to bump up your ISO to something like 400 or 800. Every time you double the ISO (100 to 200 for example) you double the sensitivity of your sensor. You can think of it like having one light on and then turning on a second light of the same wattage on in your home. This is double the light. If you were to go from 200 to 400 ISO, this would be like having two lights on and then turning two more lights of the same wattage on to have a total of four lights. (Yup, it’s that easy.)

How long your shutter stays open is based on your shutter speed. So if you go from 1/2 a second to 1 second, you have left the shutter open twice as long on one second from 1/2 of a second. By going from 1/2 a second to 1 second, your photo will be brighter by one stop. (This is the same as going from ISO 100 to 200. The photo will be brighter by one stop.)

Our last tool is the aperture – a variable sized hole inside your lens. It works in stops values too by being able to brighten (or darken) your exposure. For example, if you are at f/11 and you open your shutter to f/8 you have brightened your exposure by one stop. Again, this is like going from ISO 100 to 200. When you go from f/11 to f/8, your photo will be one stop brighter.

You may have noticed with the aperture that the larger the number is the smaller the hole is in the lens. This is due to the aperture being a fraction. Think of a delicious pie/cake. If sugar and calories were not an issue, would you rather have 1/8th or 1/11th of a slice? Most people would want more pie and choose the 1/8th (larger) slice.

Naturally, the converse of this is true. If you go from ISO 200 to 100, or shutter speed from 1 second to 1/2 a second, or f/8 to f/11 your photo will be one stop darker because half the amount to light is getting to your sensor. Of course as you go up and down each control’s values, you will be jumping by one stop.

NOTE: Your camera is most likely set up allow you to control your exposure by a 1/3 of a stop. This means you will have to click each dial three times to make a full stop. This is why you want to learn the FULL STOP range for each control.  Below is an image of the full stop range for each with examples of how each setting might affect your photo. A larger aperture hole will give you less in focus. A slower shutter speed will allow blur to show in your camera. Higher ISO settings can create visual noise. Your camera and lens may not have ALL of these settings shown but that’s OK. It’ll have enough for you to work with.


Whew, with all that knowledge as our base, let’s move on to your question – how do you make all three of these controls work for together to create a properly exposed photo? This is where BEF can come in to help.

The basic exposure formula (BEF) is more commonly known as the Sunny 16 Rule. This means that on a bright, sunny day with sunlight hitting your subject your exposure will be f/16 @ 1/ISO. To dial this into your camera, let’s have your ISO set to 100. This means your shutter speed would be set to 1/100 of a second too. As we are working in full stop scales, we can see that the closest shutter speed setting in the attached image to 100 is 1/125 of a second. That’ll work just fine. So…

Bright sunny day with ISO set to would 100 = f/16 @ 1/125 of a second.

Does this make sense? If no, email me. (

Now, let’s change the ISO to 200. What would your shutter speed change to?  Again, here is the full stop settings to help or use your camera to figure it out.


Don’t read down for the answer. Work to figure it out yourself. 😉

Did you come up with a shutter speed of 1/250th of a second? If so, then you have figured out the correct exposure for a sunny day. (Yay!)

Of course, life does not give us only bright sunny days. Sometimes haze, clouds, and night rolls in or we could be photographing inside. This is where the BEF Cheat Sheet comes into help –

If you have a look at it, you will see that haze in the air will reflect back one stop of light. This means we need to add one stop of light (make it brighter) to our exposure Sunny 16 Rule exposure to compensate. You can do this with the ISO, or the shutter speed, or aperture. Choose one. For example:
We start out on a sunny day with an exposure of f/16 @ 1/ISO. This means that if our ISO is set to 200 our exposure will be f/16 @ 1/250. Then we notice haze is rolling in so we need a brighter photo by one stop. Let’s look at ways of correcting the exposure:

Sunny Day:
ISO 200 @ f/16 @ 1/250 of a second

Hazy Day:
ISO 200 @ f/11 @ 1/250 of a second – Opened aperture one stop
ISO 200 @ f/16 @ 1/125 of a second – Slowed down the shutter by one stop
ISO 400 @ f/16 @ 1/250 of a second – Increased the sensitivity of the sensor by 1 stop

You only need to make ONE of the corrections above to correct for the exposure. You choose which one by determining if you want less depth of field (less in focus) or potentially showing more motion blur or possibly showing more noise respectively.

Got it? If not, email me. (

We are going to move on to a brighter cloudy day. Looking at the cheat sheet, we see we need to open up (brighten) our exposure by two stops (+2). This means you can choose two of the above settings and dial then into your camera to get the correct exposure. For example a new exposure could look like:

Sunny F/16 Day:
ISO 200 @ f/16 @ 1/250 of a second

Bright, Overcast Day:
ISO 200 @ f/11 @ 1/125 = opened the aperture one stop and slowed the shutter one stop
ISO 400 @ f/11 @ 1/250 = make the sensor more sensitive by one stop and opened the aperture by one stop

I won’t bore you with all the combinations because I also want to go let you know that you can also make two stop changes to one of the controls. Here are the examples:

Sunny F/16 Day:
ISO 200 @ f/16 @ 1/250 of a second

Bright, Overcast Day:
ISO 200 @ f/8 @ 1/250 of a second – Opened aperture two stops from the Sunny 16 Rule
ISO 200 @ f/16 @ 1/60 of a second – Slowed down the shutter by two stops
ISO 800 @ f/16 @ 1/250 of a second – Increased the sensitivity of the sensor by two stops

OK, I have thrown a lot at you. Let me know where you need more clarity.


How Do I Work with BDE?

Great Question:
I also have a question about the basic exposure formula. I don’t really understand how I would set the exposures. Does the ISO determine the shutter speed and aperture setting? I’m not really sure how it works.



Before I start in on BDE, let’s back up a step and answer your ISO question.  ISO settings tell your camera how sensitive to make your sensor.  If you have your camera set to ISO 100, then it is less sensitive to light and is best used in daylight or brightly lit areas that mimic daylight brightness.  When you double your ISO number, you make it twice as sensitive.  So 200 ISO is twice as sensitive as 100 ISO.  Imagine you are in a room where there are two lights with the same wattage right next to each other and both are turned on.  If you create a properly exposed photograph at 100 ISO, you could also get a same properly exposed result by turning one of the lights off and correcting only  your ISO to 200.  Because you made your sensor twice as sensitive to light, when you cut the light in half the photo will look the same.  Cool, eh?
This doubling of sensitivity is called a “stop”.  Continuing on from 100 ISO to 200, I would say that “my sensor is one stop more sensitive.”  If I doubled ISO 200 to 400, this is also considered “one stop more light” into the the camera.  (Technically, the same amount of light is going into the camera, but we photographers are not alway so technical in the way we speak.)  😉  Now a quick quiz for you…. If you changed your ISO from 100 to 400, how many more stops would you have increased you light into the camera?  Did you say two?  If so, give yourself a pat on the back.  Every time you double the ISO (100, 200, 400, 800, 1600) you are doubling the light sensitivity of the camera.  So, ISO 100 to 1600 is a change of four stops more light.  Got it?  Cool.
Now for something to pay attention to.  When you change your ISO from 100 to 1600 you are moving four stops, but this does not mean that you have “increased your light” by 4 times the amount of light.  Remember, you are doubling the each stop.  This means that you are creating the simple equation of 2 x 2 x 2 x 2 = 16 times more light.  (Ooooo, that is a good quiz question, don’tcha’ think?)  😉
We have been talking about doubling the light each stop and I have a feeling that you are starting to get your head around it so I am going to reverse the scenario for you.  Imagine that your ISO is set to 400 and you want to bring it down to 200.  What happens then?  Naturally, you half the amount of light.  So ISO 400 to 200 makes the sensor 1/2 as sensitive.  The halving of the half also goes into play when you move more than one stop.  How much less sensitive is 1600 ISO to 100?   If it helps, think like  you are using measuring cups.  You start with a full cup, go down to a 1/2 cup, then down to a 1/4 cup, then down to an 1/8 cup, and finally down to a 1/16 cup.  So when you change your ISO from 1600 down to 100 your sensor is 1/16th less sensitive.  This is like taking 16 lights of the same wattage and then turning them off until you are using one light.  That is a big change.
Whew, that was a lot of take in.  If you need to look up and take a breath before we move on, please do.  🙂  We are about to dive into BDE.
Ready?  OK, go get your camera if you want.  Sometimes it’s easier to understand what is going on if you dial in the changes.  If it gets to be too much, then just let it be a supporting friend next to you.  😉
BDE (basic daylight exposure) is pretty easy, but let’s start from the beginning.  In the real-world, BDE is known as the Sunny/16 rule.  Technically, BDE = ISO @ f/16 on a bright sunny day.  (This is another good quiz question.)  So on a full-sun day with no clouds nor haze blocking the sun’s light, your exposure when your camera is set to ISO 100 will be 1/100th of a second at f/16.  As we are working in full stops this term, we adjust the shutter speed to be 1/125th of a second.  (The tiny quickening of the exposure will not affect your exposure much.)  Essentially, on a bright sunny day, you will:
  1. Set your aperture to f/16
  2. Set your ISO to a number that feels good for you – usually 100 or 200 is better for full sun
  3. Then you will correct your shutter speed to match your ISO

Easy, right?

Now I know what you are thinking, “Yeah, that’s easy, but what do I do on a heavy overcast day?”  Another great question, thanks for asking.
On a cloudy day we have less light making it to the earth.  The clouds are blocking, absorbing, and reflecting some of the sun’s light and we just does not reach us.  This means we are going to have to adjust our exposure so that we are allowing for this lack of light.  We can make this adjustment one of three ways:
  1. Increasing the ISO – 100 to 800
  2. Opening up our aperture – f/16 to f/5.6
  3. Slowing down our shutter – 1/125 to 1/15 of a second

NOTE: You only need to change one of the tree options, not all three at the same time.  Making all three changes will give you a completely overexposed photo.  You don’t have to trust me, try it out outside.

Back to the lesson: I am betting you noticed that I have let in three stops more light with my exposure for each of these options.  How do I know to ‘open up’ the exposure by three stops?  I checked my handydandy BDE cheatsheet found here – – and in our Resouces section of Week 2.  For heavy overcast days, it tells me  BEF + 3 Stops.  The “+ 3” is telling me to add 3 stops more light to my exposure from the BDE.  It is a good idea to have this cheatsheet with you when you photograph so feel free to print it out and stick it in your camera bag or photograph it with your phone and then mark it as a favorite so you can access it easily.
Please keep in mind that you do not have to change only one option above to get the correct exposure.  You can pick and choose what you want to change, but you only need to brighten your exposure by three stops.  You can increase your ISO by one stop and slow your shutter by two stops.  You can also adjust all three by one stop more light.  Let’s take a closer look at this.  First I am going to set up a full stop range of ISO, apertures, and shutter speeds so that you can refer to them as needed as I make exposure adjustments.
                 ISO: 100  200  400  800  1600  3200
         Aperture:  f/1  f/1.4   f/2   f/2.8   f/4    f/5.6   f/8      f/11     f/16     f/22      f/32      f/45
Shutter Speed:  1′   1/2    1/4   1/8   1/15   1/30  1/60  1/125  1/250  1/500  1/1000  1/2000  1/4000
Here all some examples of equivalent exposures:
ISO 100 f/16 @ 1/125  – This is BDE for a bright sunny day before the adjustments for heavy overcast
ISO 800 f/16 @ 1/125 – Increasing only the ISO by three stops
​ISO​ 100 f/5.6 @ 1/125 – Opening up only the aperture by three stops
ISO 100 f/16 @ 1/15 – Slowing down the shutter by three stops
ISO 200  f/8 @ 1/125 – Increasing the ISO by one stop and opening up the aperture by two stops
ISO 400 f/16 @ 1/60 – Increasing the ISO by two stops and slowing down the shutter by one stop
ISO 100 f/11 @ 1/30 – Opening up the aperture by one stop and slowing down the shutter by two stops
ISO 200 f/11 @ 1/60 – Increasing the ISO by one stop, opening the aperture by one stop, and slowing down the shutter by one stop

​We can keep going with the potential equivalents, but I can see your eyes are starting to glaze over from here.  🙂

OK, that was a lot of information.  If you need to go through it a couple times, please do.  Once you have this down, you understand the backbone of creating properly exposed photographs.  As photography is based on the speed of light, this will never change.  🙂
If you have any questions on any of this material, please let me know what they are.
Take care,