Understanding Exposure Value (Podcast 630)

Understanding Exposure Value (Podcast 630)


Visit Library for MBP Pro eBooks

This week we’re going to take a look at Exposure Value or EV, and I’ll explain what it is, why it’s useful, and why I’ve spent almost every waking minute for the last 17 days building a new Exposure Shift Calculator for our Photographer’s Friend app, which we’ll use for some of my explanations.

When we talk about exposure, we generally use aperture, shutter speed, and ISO settings to relay the absolute values of our exposure, but then if you want to change one of the values while maintaining the same exposure, you have to change one or both of the other settings in the opposite direction. For example, if you are using an aperture of f/8, with a shutter speed of 1/250 of a second, at ISO 200, and I recommend that you change your aperture to f/11, which is one stop smaller than f/8, and therefore lets in half the light, you would need to adjust the other settings to counter that change.

You might change your shutter speed from 1/250 of a second to 1/125, which is twice as long, and therefore lets in twice as much light, so you maintain the same exposure. If though, for example, 1/125 of a second might be too slow and you don’t want to risk your subject moving during the exposure, making them blurry, you might decide to increase your ISO from 200 to 400, which makes it twice as sensitive, and brings your exposure back in line.

This can get a little bit confusing, especially if for example, you don’t want to change your aperture from f/8, because it provides just the right amount of depth of field for the photograph you are making, you then have to think about how you could make the same change with the other settings. If you are happy with your shutter speed, you could of course just change your ISO from 200 to 100, making it one stop less sensitive, and you’d have the same exposure as you would if you’d changed your aperture from f/8 to f/11.

Stops Explained

Although people sometimes refer to the changes made to exposure as steps, it’s more common to use the term “stop”. Before we go on, although this is pretty basic photography theory, let’s just recap that by aperture stops from say f/1.0 counting in full stops would go from f/1.0 through f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16 and higher. Depending on how you have your camera set up you might have half stops between these, but generally, most cameras and light meters use third stops, so for example, between f/5.6 and f/8 you will have f/6.3 and f/7.1, though this varies slightly sometimes with different manufacturers. It’s also worth noting that the smaller the number, the larger the aperture, so a lens set to f/5.6 lets in twice as much light as when it’s set to f/8, and f/11 lets in half as much light as f/8.

Stops in shutter speed terms are calculated by doubling or halving the time. For example, if your shutter speed is 1/250 of a second, making it one stop slower would be 1/125 of a second, and that is also one stop lighter because the light hits the sensor for twice as long. Making 1/250 of a second one stop faster takes it to 1/500 of a second, which is also one stop darker because the shutter is open half the time. This continues even when we’re doing long exposures of more than a second. One stop longer than 5 seconds is of course 10 seconds, and 20 seconds is one stop longer again.

ISO stops can be a bit confusing again, but similar to shutter speeds, you just keep doubling or halving the value for each stop. ISO 200 is one stop more sensitive or brighter than ISO 100. ISO 400 is one stop brighter than 200, and two stops brighter than 100. If we keep going, we’ll work through ISOs 800, 1600, 3200 and 6400 etc. The thing to be careful with of course is that very high ISOs can start to introduce noise or grain to your images, but I’ll regularly shoot at ISO 5000 or 6400 if necessary to get the shot. It comes down to testing your camera to see how much noise is introduced in various conditions and how comfortable you are with it.

Exposure Value Stops

So, following that recap, let’s talk about Exposure Values, which are also referred to as stops, but they can be more useful because when you refer to exposure in EV or Exposure Values, it’s not tied to any one setting. According to Wikipedia, the Exposure Value system was invented in the 1950s and uses a relatively simple formula to calculate a value that can be used to represent any combination of our camera settings.

The EV scale can also be mapped to various lighting conditions, for example, if you’ve heard of the “Sunny Sixteen” rule, which is a basic guideline to set your camera aperture to f/16 and use your ISO as the shutter speed, so at ISO 100, you’d set your shutter speed to either 1/100 or 1/125 of a second. This will get you a relatively good exposure on a sunny day, hence the name, sunny sixteen.

Well, on the EV scale, the sunny sixteen rule equates to 15 EV. On a slightly overcast day, you might open up your aperture from f/16 to f/11, one-stop wider, and this would mean you were shooting at 14 EV. For an overcast day, you might go to f/8, another stop wider, and that is EV 13. Conversely, you might increase your ISO from 100 to 200 for a slightly overcast day or from 200 to 400 for an overcast day, and of course, you could change your shutter speed, but if you have an Exposure Value to work to, it’s pretty easy to recalculate your settings.

EV zero

If we keep going back, the zero base for our scale can be represented as an aperture of f/1.0 for one second at ISO 100. This is EV o (zero). We can go darker, using negative numbers. For example, on the EV scale we have the Aurora Borealis at between -3 and -6 EV, and the Milky Way and Galactic Core at between -11 and -9 EV. I actually found these old values to be a little bit too dark if I compare them to my own images, such as for example, the settings I used for this photograph of the Galactic Core that I shot on my Namibia Tour this year.

Milky Way Galactic Core
Milky Way Galactic Core

I shot this at f/1.4 which is one EV more than f/1.0, putting me at EV 1. I was using a shutter speed of 5 seconds, so to continue with our mental arithmetic to see how this changes our Exposure Value number, first I double the exposure from one second to two, which takes the EV back to zero, then double the exposure again to four seconds, which takes us to -1 EV. Another second to 5 is one-third of a full stop, so that takes our EV to -1 ⅓.

I also changed my ISO from 100 to 3200, so let’s see how this affects the Exposure Value. First, changing from ISO 100 to 200 makes my sensor twice as sensitive, so my Exposure Value goes up by one stop to -0 ⅓. Doubling the ISO again to 400 is another stop, so we’re back into positive numbers with 0 ⅔. 400 to 800 ISO gives us 1 ⅔ EV and 800 to 1600 is 2 ⅔ EV, then finally 1600 t0 3200 is 3 ⅔ EV.

EV Increases as ISO Increases

You might have noticed there that calculating ISO changes can be a bit confusing. For me at least, it seems as though the scale is going the wrong way, but because the EV represents our cameras ability to capture an exposure based on how sensitive the film is, the Exposure Value goes up as we make the sensor more sensitive. Before I started to really look into how to calculate Exposure Value, I would certainly have guessed the opposite way, so this has taken some getting used to.

I guess it’s easier to think of EV as the target, as in the Exposure Value of the subject, not the base, which is the settings on the camera. For example, I’ve just used a Light Meter to take an incident reading of the light on this very slightly hazy summer’s day in Tokyo, and my reading was EV 14 ⅓. We can actually adjust the sunny sixteen rule to understand that I’d get a good exposure at the moment by reducing my exposure by two-thirds of a stop from 1/125 of a second to 1/80 of a second at f/16. We’ll come back to some more examples that will make this clearer, but for now, let’s talk a little more about why using the absolute values of aperture and shutter speed etc. isn’t ideal.

Exposure Shifts

When we’re shooting on my Japan Winter Wildlife tours, we are generally using Manual Exposure, to ensure that our subjects stay well exposed whether they are over a white snowy background or a darker background like trees or the sky. This works great when the light is constant, but if there are patchy clouds, we have to change our settings quite regularly, so I shout out that I’m changing my settings to the group.

Ruffled Feathers
Ruffled Feathers

If I simply shout out that I’m increasing my exposure by one stop, which is the same as saying I’m increasing my exposure by one EV, someone will invariably ask for actual settings in aperture, shutter speed, and ISO form. Then, if for example, I say f/11 for 1/1000 of a second at ISO 800, I often get asked, what would that be if I’m at ISO 400, or what if I’m at f/8, and it’s understandable because this can be a bit confusing.

Exposure Shift Calculator

To help with this kind of exposure shift, I received an idea from listener Steve Jarrel last year, for me to add a third calculator to our Photographer’s Friend app for iOS. The implementation I’ve come up with is slightly different, but the idea is basically the same, so I’ve just this morning finished some very complicated development to create a third calculator called the Exposure Shift Calculator. This has taken so much extra work, and is such a big change that I’m actually going to make this a paid upgrade to a new version of our app, but I’m currently looking into a way to provide a pseudo upgrade price for current version 2 owners, and more details of that will follow over the next week or so.

Today though, I wanted to introduce you to the new calculator to help shed a little more light on this discussion about Exposure Values. Because Exposure Values are at the core of all exposure calculations, it is at the core of my new Exposure Shift Calculator. Here’s a screenshot from an iPad Air, showing the calculator set at zero EV, which as I mentioned is the value you get with an aperture of f/1.0 for one second with ISO 100 (below).

Exposure Shift Calculator EV0
Exposure Shift Calculator EV0

When you first start using the calculator, you can of course dial in any combination of camera settings, but we’ll work from EV zero, for now, to show you how this works. If you want to store your original settings for later reference, just tap the large Store Current Settings button in the middle of the screen, and your settings will be displayed there until you tap the settings again, which clears them and brings back the Store Current Settings button.

I might, for example, use the calculator to find some settings to give me a good exposure at 14 ⅓ EV on this sunny day in Tokyo, and as we can see if I select an aperture of f/5.6, and leave my ISO at 100, I would need to set my shutter speed to 1/640 of a second. In this next screenshot (below) I’ve stored my EV zero settings for reference, and dialed in my new settings so that you can see how the store function works.

There are two ways to experiment with your settings after this though, starting with locking a single dial. If you tap the Aperture, Shutter or ISO dial labels, that label turns into my teal blue color and the padlock shows that it is locked, and now when you turn one of the unlocked dials, the other unlocked dial will automatically update to a value that maintains the same exposure. I’ve locked the original settings in the middle of the screen for reference, and then locked the ISO dial, which would be useful say if you were shooting with film and literally could not change the ISO until the end of the roll, or for example if your ISO was already very high and you don’t want it to go any higher.

Exposure Shift Calculator at EV 14 2/3 ISO100
Exposure Shift Calculator at EV 14 2/3 ISO100

I decided that I wanted to change my aperture to f/14, my go-to aperture for most of my landscape work, and you can see that the calculator automatically calculated that I would need to change my shutter speed to 1/100 of a second to maintain my Exposure Value of 14 ⅓. I can of course then tap the aperture dial to lock that at f/14, and if I change the shutter speed dial, it will give me a new ISO to use, to maintain the same exposure. Note though, that when you lock an individual dial that enables the ISO value to be recalculated, the EV will change, because increasing the sensitivity of the ISO increases your EV, so the other unlocked dial has to move in the opposite direction to maintain the exposure.

The Challenge

That concept led me to what turned out to be the most difficult feature to code, the Exposure Value Lock. If you tap on the Exposure Value number or the padlock to its right, any individually locked dials will be unlocked, but now when you spin any dial, the other two dials will automatically update to maintain the same Exposure Value. This was particularly difficult because not only did I have to calculate two other dials simultaneously, the ISO dial has to turn in reverse to maintain the Exposure Value. 

Exposure Shift Calculator Aperture Locked
Exposure Shift Calculator Aperture Locked

For example, if I lock the aperture dial at f/14 and change the shutter speed from 1/100 of second to a 1/200 of a second, the ISO would change from 100 to 200, to counter the shutter speed change to maintain the same exposure, but because increasing the shutter speed increases the EV by one stop and making the ISO more sensitive also increases the Exposure Value, my EV changes from 14 ⅓ to 16 ⅓.

Exposure Value Lock

So, to lock the EV, I actually have to rotate the ISO dial in the opposite direction to ensure that the Exposure Value is maintained, rather than the Exposure. I know that sounds weird, but that’s what this took to achieve and actually provide a useful EV Lock feature. If for example I have a meter reading of 16 ⅓  wanted to  EV, and I wanted to open up my aperture to f/2.8 for some nice shallow depth of field, by locking the EV and selecting f/2.8 on the aperture dial, the calculator gives me a shutter speed of 1/1000 of a second at ISO of 1000.

Calculated Exposure Value Locked Shift
Calculated Exposure Value Locked Shift

That’s useful to see your options while maintaining the EV, but in this case, if you know that you want an aperture of f/2.8 and because you know that you have plenty of light, rather than locking the EV and going fully automatic, it would be better to simply lock the ISO and move your aperture dial to f/2.8 and then you’ll get your new shutter speed of 1/5000 of a second, for a great outdoor exposure on a theoretically very bright sunny day.

ISO Locked Exposure Shift to f/2.8
ISO Locked Exposure Shift to f/2.8

Send To Buttons

If, for example, you don’t want the water in the fountain behind your model to be completely frozen by a shutter speed of 1/5000 of a second, you might decide to apply some neutral density filters, and to save you the trouble of remembering your shutter speed, I’ve also added a To ND Calc button at the top of the screen, above your calculated shutter speed, which, as you might imagine, will send your new shutter speed directly to the ND calculator and open it for you. This is also useful if you have calculated a shutter speed of five seconds or more and need a timer. Just jump over to the ND Calculator and hit the timer button.

Likewise, the To DoF Calc button will send your aperture to the Depth of Field calculator so that you can see how much depth of field you have at the currently selected or calculated aperture.

So, I hope this has helped a little if the concept of Exposure Values wasn’t something that you are familiar with. As with the other two calculators, as well as actually helping you to work in the field, they are great for learning the theory behind exposure and depth of field, as well as teaching it. Even if you have all this down, there’s nothing like being able to turn dials and show the effects of your changes to help people understand this stuff. Then hopefully when you are advised to increase your exposure by one or two stops, you’ll be better equipped to calculate the difference in your head, or reach for your iPhone and open the Photographer’s Friend.

Photographer’s Friend 3 Coming Soon!

As I said, my current plan is to make this a paid upgrade, so if you like what you see, but don’t already own version two, then please wait for a few days until I release version three. If you are reading or listening after more than a few days into September 2018 though, version three should already be available. And for those of you that have version two, I will try to provide a reasonable upgrade path, details of which will be provided in an update to version two of the app. If you don’t need the Exposure Shift calculator, you are more than welcome to continue to use version two, and I have a few improvements for version two that will be released very soon as well, so you won’t be left out to dry.

Freebie Post

This post is unlocked for non-Patrons as it is a sponsored post or advertising Martin Bailey Photography products. If you found it useful and would like to unlock all other posts please click the button below. Thank you for your support!

Become a Patron!

 


Show Notes

You can get Photographer’s Friend in the Apple App Store here: https://mbp.ac/pf

I’ll update this post with a link to version three soon! If I forget, see the ad below. 🙂

Music by Martin Bailey


Audio

Subscribe in iTunes for Enhanced Podcasts delivered automatically to your computer.

Download this Podcast in MP3 format (Audio Only).

Download this Podcast in Enhanced Podcast M4A format. This requires Apple iTunes or Quicktime to view/listen.


Podcast 206 : Dynamic Range

Podcast 206 : Dynamic Range

Today we’re going to talk about Dynamic Range. Dynamic Range is one of those words that crops up a lot, but is sometimes not fully understood. Indeed, I don’t profess to fully understand all the fine details, but I know enough about Dynamic Range to be useful to me when making my own images, so I figured I’d share this today, along with some information from a couple of great online resources and some general observations.

What is Dynamic Range?
In simple terms, Dynamic Range is the difference between the darkest thing and the lightest thing that your camera can capture and still retain detail in these areas of the subject. I guess would could think of it as pure black and pure white, because that’s what will happen as you hit the boundaries, and that may often be fine, but most things in the real world have some level of texture and shades, tonal values other than pure black or pure white. If I am photographing a white object though, I am going to want to be able to make out the texture in that object or subject, and if I overexpose the subject, I lose that detail, and the information recorded in the image file becomes just pure white.

I should mention that if you shoot RAW, and you should if you care about the quality of your images, you can bring detail out of the highlights and shadows to the tune of around one stop over or underexposure, but this still depends on you having some detail in the over exposed highlights or deep, seemingly plugged up shadows. If you were to sample an area that’s overexposed in Photoshop and find that the RGB values have gone to #FFFFFF, or pure white, for any significant amount of the image, there’s no texture in there at all. There’s no way to bring any detail back in post processing. The same goes for something pure black in the deep shadow areas. Once the shadows go to #000000 for any significantly large area, the details are gone.

Shoot for the Highlights!
We’ve spoken before about exposing for the highlights, and most of the time this is going to be true. It’s of course always best to get the exposure as good as possible in camera, but if you lose control of your exposure for one reason or another, and your histogram starts to clip, hitting that right shoulder, then you’ll start to lose detail in those whites, or whatever color you are overexposing. It’s important to note that if you have an RGB histogram, use it. You can blow out just one channel, like the Red channel, and it doesn’t always show up in the black and white histogram, and it can look pretty bad to have just one channel blown out. Sometimes even worse than when you blow the whole thing out. The point is to try to get the brightest part of your scene close to, but not touching the right shoulder of your histogram. When you do this though, if the lightest and darkest values in your chosen scene are greater than that of your camera’s dynamic range, you are going to start to lose detail in your shadows as they start to plug up.

When NOT to Shoot for the Highlights
There are times when you will allow large parts of an image to blow out, for the sake of the main subject, as in image number 2308 (below). Here the histogram will spike to the right, as we see to the in this histogram, well and truly hitting the right shoulder. But when shooting this I knew that the sky was going to blow out, so I chose to ignore the histogram. I concerned myself only with getting nicely exposed, fresh green leaves. Had I exposed for the highlights, not only would the greens would be muddy, the bark on the tree trunks would have been very dark, and probably even under exposed.

Big Tree and Fresh Leaves

Big Tree and Fresh Leaves

You do have to be careful here mind, because when you do allow the sky to overexpose like this, it will gradually start to bleed into the important main subject. I like this effect to a degree, as you can see in this image. I think it even adds a little sparkle to the overall effect. But there are limits. If you ignore a bright light source too much, it can bleed into the main subject so badly that it becomes totally washed out, rendering the image pretty much useless.

EV Aperture
1.0 1.4 2.0 2.8 4.0 5.6 8.0 11 16 22 32
−6 60 2 m 4 m 8 m 16 m 32 m 64 m 128 m 256 m 512 m 1024 m
−5 30 60 2 m 4 m 8 m 16 m 32 m 64 m 128 m 256 m 512 m
−4 15 30 60 2 m 4 m 8 m 16 m 32 m 64 m 128 m 256 m
−3 8 15 30 60 2 m 4 m 8 m 16 m 32 m 64 m 128 m
−2 4 8 15 30 60 2 m 4 m 8 m 16 m 32 m 64 m
−1 2 4 8 15 30 60 2 m 4 m 8 m 16 m 32 m
0 1 2 4 8 15 30 60 2 m 4 m 8 m 16 m
1 1/2 1 2 4 8 15 30 60 2 m 4 m 8 m
2 1/4 1/2 1 2 4 8 15 30 60 2 m 4 m
3 1/8 1/4 1/2 1 2 4 8 15 30 60 2 m
4 1/15 1/8 1/4 1/2 1 2 4 8 15 30 60
5 1/30 1/15 1/8 1/4 1/2 1 2 4 8 15 30
6 1/60 1/30 1/15 1/8 1/4 1/2 1 2 4 8 15
7 1/125 1/60 1/30 1/15 1/8 1/4 1/2 1 2 4 8
8 1/250 1/125 1/60 1/30 1/15 1/8 1/4 1/2 1 2 4
9 1/500 1/250 1/125 1/60 1/30 1/15 1/8 1/4 1/2 1 2
10 1/1000 1/500 1/250 1/125 1/60 1/30 1/15 1/8 1/4 1/2 1
11 1/2000 1/1000 1/500 1/250 1/125 1/60 1/30 1/15 1/8 1/4 1/2
12 1/4000 1/2000 1/1000 1/500 1/250 1/125 1/60 1/30 1/15 1/8 1/4
13 1/8000 1/4000 1/2000 1/1000 1/500 1/250 1/125 1/60 1/30 1/15 1/8
14 1/8000 1/4000 1/2000 1/1000 1/500 1/250 1/125 1/60 1/30 1/15
15 1/8000 1/4000 1/2000 1/1000 1/500 1/250 1/125 1/60 1/30
16 1/8000 1/4000 1/2000 1/1000 1/500 1/250 1/125 1/60
17 1/8000 1/4000 1/2000 1/1000 1/500 1/250 1/125
18 1/8000 1/4000 1/2000 1/1000 1/500 1/250
19 1/8000 1/4000 1/2000 1/1000 1/500
20 1/8000 1/4000 1/2000 1/1000
21 1/8000 1/4000 1/2000
22 1/8000 1/4000
23 1/8000

Exposure Value?
Before we can start to talk about how much dynamic range our camera’s have, let’s look at the units of measurement used. Dynamic Range is measured in EV, or Exposure Value, which can also be termed a “stop”. One “EV” is one “stop” in exposure terms. We know that there are three settings on our camera that affect the exposure, and that is the Aperture, the Shutter Speed and the ISO. Changing any combination of these settings will modify the EV. The chart to the right shows the shutter speeds required for each aperture from F1 to F32 to capture a subject with the Exposure Value from -6 to 23 EV at ISO 100. If we were to create a chart for ISO 200, basically all of the shutter speeds would be halved, and of course halved again for ISO 400, and so on.

An aperture of F1 is basically a lens that is as wide as it is long. What I mean is, if you have a 50mm focal length lens, to make it F1, it would have to have a 50mm wide aperture when it’s wide open. The common 50mm F1.4 lens has an aperture of about 36mm when used wide open. You get this by dividing 50 by 1.4. If you close the 50mm down to F2.8, the aperture will be around 18mm and so on. Another example I like to use to emphasize this calculation is the 600mm F4. If you divide 600 by 4, you get an aperture opening of 150mm, or 15cm, or about 6 inches. That sounds pretty wide, but if you’ve ever looked into the barrel of a 600mm F4 lens you’ll know that it has huge lens elements, but I digress.

If we start thinking about this from F1.4, you can see from the chart that at F1.4 an EV of one requires a one second exposure. As you increase the Exposure Value, you can see the shutter speed halve with each stop, until you get to the fastest shutter speed for most cameras on the market today, which is 1/8000 of a second at EV 14. If your scene is brighter than EV14, the only way you can shoot it without overexposing it is to close down your aperture, or if you don’t want to do that, say because you want to shoot with a wide aperture for a shallow depth-of-field, you can add a Neutral Density filter to cut out light and in turn reduce the EV. I hope I’m making sense. If I’m not, I suggest you study the EV chart on the blog a little more. It’s pretty straight forward.

How Much Dynamic Range?
The human eye can see around 24 stops of dynamic range because the pupil opens and closes dynamically as we scan a scene. If you think about it, we are pretty much stuck in Shutter Priority mode, with automatic ISO. As we look at the world around us, if we look at something bright, the pupil get small to stop the bright areas from being too bright and in our cases even possibly damaging our eyes. If we look into the shadows, our pupils open up to reveal some detail in the shadows, even at the expense of some very bright areas in our peripheral vision. When you open your eyes at night, way when you’re laid in bed, you’ll probably notice a lot of grain, and the world is pretty much black and white, because you lose the ability to record the colors and tonal values the higher our brain sets our ISO. This all amounts to around 24 stops of dynamic range in pretty much full auto, but If we could stop the pupil from opening or closing, essentially making just one frame, it is estimated that we see between 10 to 14 stops. If you are wondering where I got this information from, it’s from the Cambridgeincolour.com Web site. They have a great article on Dynamic Range, which I’ll link to in the show-notes.

I’m sure by now, those of you that have never investigated this are wondering what dynamic range modern digital SLR cameras are recording single images in. Well, the 5D Mark II is said to have a dynamic range of just under 12 EV, so it’s actually very similar to the human eye, if we could fix the aperture in our eyes. Like the human eye, the camera’s dynamic range reduces as you increase the ISO. The 5D Mark II captures just under 12 EV when the ISO is set between 50 and 200. As you increase the ISO, the dynamic range decreases, as does the tonal range of your images. It’s not a rapid decrease mind. You lose just under two stops to around 10 EV as you drop down through ISO 400 to 1600, then another EV for every stop of ISO from then on. That means you drop to 9 EV at ISO 3200, 8 EV at ISO 6400, 7 EV at ISO 12800 and just under 6 EV at ISO 25600.

This data by the way is from DxO labs, on their DxO Mark site. If you want to see all kinds of information on your own DSLR, go to dxomark.com and select your camera brand and model from the pull-downs on the top page. I also checked the information for my 1Ds Mark III, and was pleasantly surprised to see that it actually beats the 5D Mark II just by a hair with a dynamic range of 12. Nikon users will also be pleased to hear that the D3X has a dynamic range of 13.7, and the D3 and the D700, as well as the D3X all beat the 1Ds Mark III and the 5D Mark II on dynamic range. The good thing is that we all beat the Hasselblad H3DII 50. The only camera that beats both the top of the range Nikon and Canon DSLRs as of August 2009 is the Phase One P65+. This is a 60MP medium format camera though, and will cost you in advance of $40,000 US, for the basic kit including an 80mm lens, so I don’t think many of us will be losing sleep over this.

Now, I know that some of you will be jumping up and down in your seats now wanting to talk about High Dynamic Range, but we’re not going to get into that today. Yes, you can shoot multiple images, or use multiple exposures from a single RAW file to create images with higher dynamic range than the current technology allows, but I personally don’t really shoot HDR, and I only like to talk about things that I either do myself or have a pretty good understanding of.

Flowering Lotus with Seed Pod

Do We Really Need More Dynamic Range?
When you think though, that modern DSLRs are now capturing roughly the same dynamic range as the human eye with a fixed aperture, do we really need much more Dynamic Range? I’m going to play devil’s advocate here and suggest that we probably don’t. I believe that the image above was enhanced by the sparkling highlights shining through the leaf canopy. There are times when the contrast in a scene is simply too great, and I’m sure we’ll enjoy it as camera manufactures find ways to increase the dynamic range of the sensors, but you know what? When that happens, I can definitely see myself grabbing that Blacks slider in Lightroom and deepening my shadows. I don’t think we necessarily need to see detail in shadows in every image. Take a look at image number 2333 to the right. This white Flowering Lotus stands out beautifully against the dark shadow background formed by some trees in the late afternoon. The only thing that was not pretty much pitch black was that area of grey that we can see to the right of the seed pod. I think this was the trunk of one of the trees. This is pretty much as my camera recorded the scene, except I’ve converted it to black and white.

(I’ve added three more color images to the album at the bottom of this post as other examples of where I’d deliberately plug the shadows by dragging the Blacks slider in Lightroom to the right, if of course, my camera had a wider dynamic range than it does. These shots are all pretty as the camera rendered the shot.)

If my camera was capturing say 24 EVs, like our eyes with their automatic aperture control, although it will be nice some of the time, I really think that there’ll be occasions when it’s just too much. It won’t feel natural to use. I’m sure I’d want a custom setting on my camera to restrict Live View and maybe even the preview images on the LCD to only display 12EV or any incremental value with a slider for example. I don’t necessarily want to see the full gamut on my LCD. I can see most of it through the lens of course, because I’m using my 24 EV dynamic range eyes, but I feel that the feedback we get on the LCD either in Live View or in the image we captured, can help us to use the shadows to effect, that I fear we could lose if dynamic range gets too great in every image. Of course we would adapt, and it may just become another aspect of the photograph that we pre-visualize. We might even just get totally accustomed to 24EV shots, and they start to look natural too us. Right now though, I like the deep shadows that we get in some situations with today’s cameras. Hopefully this will give you a little food for thought though.


Show Notes

Great Dynamic Range article: http://www.cambridgeincolour.com/tutorials/dynamic-range.htm

Camera dynamic range and other measured data: http://www.dxomark.com/

Music from Music Alley: http://www.musicalley.com/


Audio

Subscribe in iTunes for Enhanced Podcasts delivered automatically to your computer.

Download this Podcast in MP3 format (Audio Only).

Download this Podcast in Enhanced Podcast M4A format. This requires Apple iTunes or Quicktime to view/listen.


Exposure and Manual Mode (Podcast 10)

Exposure and Manual Mode (Podcast 10)

Hello and welcome to episode ten. First, I want to announce the winner of October’s prize for members active in the forum. Congratulations to Marisa Firpi. An original print of the photograph you chose, which was “Distant Tokachi Mountain”, is in the post on its way to you. This is photo number 663 if anyone would like to take a look. The print was creating with an Epson PM-4000PX printer, which I believe is the Stylus Photo 2200 in the US. This printer uses pigment or archival ink, and I am using compatible paper, so you can expect your print to last longer than a standard photograph under the same conditions.

So, on to this week’s main topic… Today I’m going to talk about Exposure, Exposure Compensation and the times that I switch to Manual mode when shooting. There’s a lot to take in, so you might need to concentrate a little if you are not entirely confident in these areas.

Typically I use Aperture priority mode, but under certain condition I switch to manual mode and set the aperture and priority myself. I’ll explain more about that in a moment, but first, let me explain briefly about the relationship between the aperture size, the shutter speed and the ISO settings. For some of you this will just be a recap, but I’m sure some listeners will benefit from a brief recap.

When we talk about the aperture size, we often use the term f-stop. The f here stands for factorable. Basically, your camera will have a series of aperture values which you can set. The smallest number such as F1.4, F2.8 or F4 etc represents the largest aperture size, and the largest numbers, such as F22 or F32 represent the smallest aperture size. I know it’s weird to have the smallest number equaling the largest aperture and visa versa, but it would make this Podcast too long to go into the reasons why. Let’s just remember it this way.

The key aperture settings are F1, F1.4, F2, F2.8, F4, F5.6, F8, F11, F16, F22 and F32. Some lenses will go smaller than F32 to F45 or even F64, but they are not so common. With each stop, counting down from the smallest number, or largest aperture, we are effectively halving the size of the hole that lets light into your camera. Depending on your camera, you may also have half or third stops, but the numbers I just gave are the primary stop values, so let’s concentrate on them, and if you can, it will help you greatly when shooting in manual mode to memorize them.

Now, to help us to change these settings while shooting with some simple mental arithmetic, we should remember that there is a direct relationship between the Aperture values and the shutter speed and the ISO. To illustrate this, if you have your camera available you could try it right now, if not, just keep on listening. This will work on a digital camera or a film camera that allows manual setting of the ISO and see the aperture and shutter speed settings. First set your camera to aperture mode. Next set your ISO to 100 and aim your camera at a scene that you know will have constant light for a while, then half press the shutter button to have the camera meter the scene and show you the aperture and shutter speeds. Make a note of the aperture and shutter speeds. For the sake of this example, let’s say that you have set your aperture to F8, and the camera is giving you a shutter speed of one 250th of a second. If you then change the ISO to 200, you will now see that the shutter speed changes to a 500th of a second. Change the ISO again 400 and you’ll see that the shutter speed changes to one 1000th of a second. So we see that changing the ISO is doubling the sensitivity and therefore halving the time needed to make the same image exposure.

Now, let’s return the camera’s ISO settings to ISO 100, and you’ll be back to F8 at 250th of a second. This time, let’s change the camera’s aperture setting. Remember that F5.6 is one f-stop larger than F8, so obviously, when we change the aperture from F8 to F5.6, we’ll be letting in twice as much light. So what’s going to happen to the shutter speed? That’s right! It will be halved to one 500th of a second. This is the same as changing the ISO from 100 to 200, and doubling the sensitivity of the film or sensor. To make the point, let’s make the aperture smaller by stopping down to F11. Now you’ll see that the shutter speed changes from one 500th of a second at F5.6 through the original 250th of a second at F8 to 125th of a second at F11. If you stop down further to F16 you’ll again halve 125th of a second to on 60th. I know that half of 125 is actually 62.5, but your camera will display one 60th. Again, let’s just remember this as it is.

Of course, if you were to set your camera to shutter priority, you could do a similar thing by setting the shutter speed to 1/250th of a second, and the camera would select F8 for you. If you change the shutter speed to 1/60th of a second it would change the aperture to F11 for you. It’s all relational.

If by the way you are getting inconsistent reading while trying this, maybe you could try this at night under artificial lighting, such as the light bulb in your living room. You might also want to put your camera on the table or even on a tripod to keep it steady during the operation, so that the readings will be constant.

If you own a hand-held light meter, you can also play around with that in a similar way to get an idea of the relationship between these three settings.

Anyway, I think you get the picture. By changing any combination of the aperture, shutter speed or ISO we can change the amount of light that hits the film or digital sensor and change the exposure. Now that we know that a properly exposed image can be obtained by any combination, let’s talk briefly about EV or Exposure Value. Exposure Value is a unit used to describe the amount of light for any given exposure. For example, the starting point for the example given earlier, which is F8 for 1/250 of a second at ISO 100, has an Exposure Value, or EV of 14. And so do F16 at 1/60 of a second and F5.6 at 1/500 of a second and F2.8 for 1/2000 of a second. All of these settings will give us the same exposure as the same amount of light will hit the film or sensor. It may be easier to understand the relationship between the EV values and the shutter speed and aperture settings by look at a table I posted in my forum some time ago. I’ll include a link to this post in this episode’s notes.

Obviously being able to obtain the same exposure using different combinations of aperture and shutter speed, gives us the ability to make artistic decisions about the resulting image. That is because the size of the aperture will affect the depth of field. If we want the whole scene in focus, what we call pan-focus, we must select a small aperture such as F16 or F22 or smaller, though this also depends on the focal length of the lens and the distance from your camera to the subject on which you focus. Talking about this today though would make this Podcast a little too long, so we’ll leave that for another day. Anyway, pan-focus is often something that we want to achieve in Landscape photography to ensure that the whole scene is sharp for our eyes to explore.

If however, we want a very shallow depth of field, say for a portrait or wildlife shot in which a sharp background would detract from the main subject, we would need to select a wider aperture. So we may decide to go for an F2.8, F4 or even F5.6 aperture with longer focal length lenses.

Now, before we move on to some real-world examples, let’s talk briefly about exposure compensation. As I mentioned in last week’s Podcast, your camera will almost always try to render your scene in neutral brightness, similar to that of an 18% gray card. Now if the scene is actually very dark, say it contains a lot of black objects, or such as some of the images attached to last week’s episode, the camera will try to brighten them up and over-expose your image, so you have to under-expose to ensure that the scene is recorded accurately. Likewise, in daylight, if the scene is very bright, the camera will try to make it a neutral brightness, and therefore will under-expose the shot. So you have to over expose it to make it accurate. This practice is called Exposure-Compensation and most cameras except for the basic, fully automatic models will have the ability to compensate exposure quite easily. It’s usually as simple as turning a dial. You also need to know by how much to turn the dial of course, which I have some practical advice on.

So let’s talk about a practical application, now that we can do these exposure calculations easily in our heads. This will also illustrate the reasons why we might want to go to manual mode on occasion.

In February 2004 I went to Hokkaido, the northern-most island of Japan, to shoot wildlife. Hokkaido in February means snow, and lots of it. Snow will generally fool your camera’s meter into under exposing by around 1 to 1 and 1/3 of a stop in overcast conditions, or up to two stops in bright conditions. If you were to rely on your camera’s meter you would end up with gray snow, which I’m sure you’ll agree would not look very nice.

To make snow look white, you can compensate by moving your exposure compensation dial to plus one and 1/3, one and a half or more in brighter conditions. If the entire scene is going to be snow with no darker patches you need not worry about switching to manual mode, as the metering will be constant, so the amount of exposure compensation needed will also be constant. However, if the scene will be made up of very light patches, such as snow or light coloured sand, and dark patches, such as wet rocks or trees, depending of the metering mode you are using and where your main subject is in the frame, you camera can make all sorts of mistakes. It is under this kind of conditions that I would switch to manual mode and set both the aperture and shutter speeds myself.

Wassup!! - Japanese Crane

Wassup!! – Japanese Crane

Let’s take a look at the first photo on today’s Podcast. This is number 287, which was shot at F5.6 at 1/800 of a second. You can view the photos in iTunes or on my Podcast page which is linked to the top page of martinbaileyphotography.com. You’ll see a number of Japanese Red-Crowned Cranes on a field of snow and a dark forest in the background. I had l metered from the snow which although I don’t recall exactly, was probably giving me a reading of around 1/2500 of a second at F5.6. The camera was remember trying to give me a nice medium gray coloured snow, so this was far too fast a shutter speed. It was a hazy sunshine on that day, not full sunlight, so I didn’t need to compensate by a two full stops. To find the correct exposure, I first took a shot of the snow, with nothing else in the frame, then compensated by adding around 1 and 2/3 of a stop.

To calculate this, you can either count up two thirds from plus one stop, or down from plus two stops. To count up from one stop, start with 1/2500 and then double the shutter speed to 1/1250 of a second. Then click twice more on your shutter adjustment to go past 1/1000 of a second to 1/800. To drop back by a third from two full stops, double the speed first to 1/1250 as before, then double it again, which will give you 1/640 of a second, which is two stops. Then click back one to 1/800. You don’t have to do the mental arithmetic to find out exactly what a third is, as you know that there are three clicks per stop. Your camera will help with the finer adjustments. In actual fact, if you don’t want to remember all this about doubling the times you can just think that 1 and 2/3 is actually 5/3, so you can just click five times after what the camera is initially telling you.

If you have your camera set to use half stops and not thirds you will have just one click between stops. You will probably also have different numbers to play with to start from. This makes the example a little confusing, but I can’t go back to February 2004 and take my shots again, so I’ll just quickly mention that when I set my Canon EOS 5D to use 1/5 stops, in manual mode I have the options of 1/750, 1/1000, 1/1500, 1/2000 and 1/3000 etc. If you are using a similar scale you need to set the shutter speed to 1/750, which would be one and a half stops more than what your meter reading gave you, which would probably have been around 1/2000 of a second.

One important additional piece of advice here is that if you are using a digital SLR, it is very important to check that you are not blowing out your whites. Take another practice shot and check the histogram. If you have a spike on the far right hand side it means there are areas of your shot that are too bright. With a very white scene you should see the peak of the histogram weighted to the right side, but not right up against it. Some digital SLRs also have a flashing warning when the white is close to or actually blown out. If you see either of these warning signs, drop down by a 1/3 or 1/2 a stop and take another practice shot. Repeat this until the histogram looks good or there are no or very little areas of the image flashing the over-exposure warning. This way you should be able to ensure that your whites are white, but not blown out.

Japanese Crane

Japanese Crane

Let’s also take a look at the second shot attached to this episode, which is number 297. This time the white cranes, which are obviously the same colour and luminosity and when they are standing on the snow, are now flying against a totally dark background. I shot them in manual mode at exactly the same settings, F5.6 at 1/800 of a second. Had I left this to my camera’s meter, it would have over-exposed to brighten the dark background, and the birds would have been so blown out that there would have been absolutely no detail in the white what so ever. The shot would have been useless. Instead, you can make out detail of the feathers and the background is dark as it actually was. Another interesting thing is that even when the birds were shot flying overhead at the same F5.6 at 1/800 of a second, as in shot 280, they were still perfectly exposed. This is another scene that would have fooled the camera’s meter and again ruined the shot.

Japanese Crane

Japanese Crane

Of course there are numerous ways to ensure good exposure in high contrast scenes, such as using spot metering on your camera and using hand-held light meters etc. but getting into this right now would make this Podcast way too long, and I still have some weekend left to enjoy, so let’s leave it there for now.

For some examples of when you might want to do some negative exposure compensation to ensure a dark scene stays dark, take a listen to episode nine and look at the examples. I introduced a number of dark shots from a trip to India.

This Podcast was a little heavy going, but if you are not familiar with Exposure Values, F-stops and exposure compensation, you might want to listen to it a few times until you come to grips with this theory and the practical applications. If you have any questions, I’ll try to answer them in the forum at martinbaileyphotography.com and if I can’t, I’m sure someone will be able to.


Show Notes

The Music in the first 28 Podcasts is copyright of William Cushman © 2005, used with kind permission.


Audio

Subscribe in iTunes for Enhanced Podcasts delivered automatically to your computer.

Download this Podcast in MP3 format (Audio Only).