Posted on Monday, 30th April 2012 by Cee
Lens aperture and depth of field are closely related in photography. This tutorial explains through a series of photographs how the change in lens aperture affects the sensation of depth in your photographs. To discover how to make your viewer’s eye move around your photograph or to have it fixed at a certain point of interest, read on.
Every camera lens has an aperture. It is the hole inside the lens which lets in the reflected light from your subject. On an SLR camera and some advanced point-and-shoot cameras, you can change the size of the aperture manually. Obviously, changing the size of this aperture will determine how much light is allowed to enter through the lens which will have an impact on your shutter speed, but changing the size of the aperture has another effect that governs creativity. And that is…
Depth of Field
You’ve probably heard other photographers talking about aperture and depth of field and wondered how it relates to photography. Photographers are constantly deciding which aperture to use for their photos. In actual fact, the aperture of a lens has become so important to photographers that they are constantly concerned with the sharpest aperture and the sharpest lens and constantly changing from one lens to another after reading lens reviews that they end up spending less time taking photographs with the lenses in their current collection.
Professional photographers however, don’t fall into this pit. If you are a good photographer, you’ll know that a sturdy tripod, shooting in mirror-lockup mode and using a cable release is one of the best ways of producing sharp photographs and you can do that with the cheap lens and camera that you have right now.
So what is depth of field?
Precisely, depth of field is the area of focus in front of and behind
the focal point in a photograph
Let’s dive into this concept with sample photographs below. Before I discuss the examples, please understand how aperture is defined on your camera.
Take a look at the LCD panel on the left. The number 5.6 represents the aperture setting. This is not the size of the aperture in millimetres. Don’t be mistaken. This is the f-number that represents the aperture. How is it calculated?
Basically, f-number = Focal Length of the Lens/Size of Aperture
This tells us that there is an inverse relationship between the f-number and the size of the aperture.
Meaning that the bigger the f-number, the smaller the size of the aperture. If you have an SLR camera, some lenses will have an aperture ring which you can unlock on the lens and rotate to see how the aperture changes. It depends on the brand of lens and sometimes, some brands will only have certain subtypes of lenses that will have an aperture ring that can be changed manually. Some Nikon lenses have an independent aperture ring.
Some lens manufacturers will not put an aperture ring on their lenses because they want it to be controlled electronically on their brand cameras only. So you determine what aperture setting you want on their camera LCD by turning a dial. When you press the shutter release button, the receded diaphragms that make up the aperture (or hole) in the lens, converge to form the aperture determined by the f-number you set on your camera.
You may be wondering at this point…
What the common aperture settings are and how to decide which one to use?
The common settings are f/1.4 | f/2 | f/2.8 | f/4 | f/5.6 | f/8 | f/11 | f/16 | f/22 and f/32.
Here are a few things to remember about apertures:
- The smaller the f-number the larger the aperture. Don’t forget that! Small f-number means “big-and-wide-open” aperture. So f/1.4 would be the largest aperture here with f/32 the smallest.
- Your camera will allow in-between settings of the figures above because digital cameras allow you to change your exposure settings in halves and thirds of an exposure as well as full stops now.
- You’ll come across f/1.2 and f/1 lenses as well. These are worth thousands of pounds and owned only by photographers who know why they need them.
- There is a multiplication factor of 1.414 between each subsequent aperture setting above. This means that that f/1.4 x 1.414 = f/2. And f/2 x 1.414 = f/2.8, and so on. This factor of 1.414 allows a complete 1-stop difference in the amount of light that enters through the aperture. So f/2 allows half of the light that f/1.4 allows. F/2.8 allows half the light that f/2 allows.
Most importantly however,
Depth of field increases as the size of the aperture decreases
So let’s get to those examples now and see it for real so that you can decide which aperture setting you’re going to find useful and in which situation.
Here is an image taken at f/1.2 with an 85mm portrait lens. This is a wide open aperture with a diameter of 85mm/1.2 = 70.8mm. Remember the formula? Size of Aperture = Focal Length of Lens/f-number.
Anyway, look at how much of the image from front-to-back is in focus. I’ve focused on my wife’s right eye. Notice how there is very little in focus, in front of and beyond this focal point? On the side closest to the camera, you can see clearly that the right leg of her spectacles is out of focus. On the other side of the focal point, part of nose, the telephone and especially the living room cupboards are completely out of focus.
So the conclusion here is that very large apertures like f/1.2 and f/1.4 produce a very shallow or what some photographers call a very narrow depth of field.
So the question is, when would you desire such a large aperture? Basically, when you want your viewer’s eye to be fixated on a certain point in the photograph. Lenses with large apertures are often used by wedding photographers because they can use this narrow depth of field to bring attention to the bride’s eye make-up when shooting her morning make-up scenes before the wedding. Photographers who take pictures of products where a certain aspect of the product needs to be emphasized, for example in jewellery.
One thing you should note if you ever decide to invest in a lens with a large aperture like f/1.2 or f/1.4 is this – as far as creativity is concerned, the possibilities are endless. For a second, look at how the background is blurred out. You can get really creative with the background. Imagine a background in the image above with a huge light-coloured drape with circles of different colours on it. Those circular colours would blend in to each other beautifully with the blurring effect.
Wedding photographers know this very well and often shoot amazing photographs using such large apertures because background scenes especially on the reception dance floor are well lit and there are many people wearing the most beautiful colours.
Personally, I love large apertures
Do you need a f/1.2? Probably not yet especially if you’re starting out. However, if you are a serious beginner I would definitely invest in a 50mm f/1.4. Why? Because the 50mm f/1.4 is a lot cheaper than the 50mm f/1.2 lens. First of all, have a look at the picture below. It has been taken at an aperture value of f/1.4 and look how similar the results are to the image above which was taken at an aperture value of f/1.2.
As a guide for the focal point, the nearest end of the M on the pillow is in sharp focus. I zoomed in on this image to 100% and noticed the sharpest point that was in focus was my son’s shirt just in front of his chin. The eyes were slightly blurred and I’ve sharpened them up a little here using Photoshop. But look at how the toys and the pillows in front and behind the focal point become blurred and create a dreamy sensation.
This effect is called Bokeh
The important point to get is this however – there isn’t much difference in the depth of field from f/1.2 and f/1.4. The image below was shot at f/2.
In this image, the eyes have been brought into focus because f/2 still provides a narrow depth of field. Focusing elsewhere, for example his right shoulder might render them out of focus. Look at how the left perimeter of the subject’s head is out of focus because of the head tilting to the right. The subject’s right ear is out-of-focus more than his left ear. Having said this, f/2 is great aperture for this lens. Easier to focus than at f/1.2. The result at f/2 is quite sharp.
F/2 should only be used if you’re concentrating on a single subject. You might find it difficult to bring the eyes of two or three subjects standing in a line into sharp focus. You will need more depth. An intimate couple kissing will certainly work – you could focus on the lips.
Here’s an image at f/2.8.
This image demonstrates that at f/2.8 you can safely get a subject that is facing the camera perfectly in focus. Notice how the menu in front of the focal point (which is the face) is out of focus as well as the background.
Just like at f/2.8, pretty much all of the subject is in focus. The difference here is that the subject’s shoulders are tilted so that his body is not completely parallel with the camera. However, both shoulders including the left which is farthest from the camera are in focus.
This image has been taken at aperture f/5.6 in front of the bookshelf deliberately. If you compare it with the earlier images at f/1.2, f/1.4 and f/2.8 … Look how much more is in focus in the background. Even some of the toys on the floor behind my son are much more in focus at this smaller aperture of f/5.6.
F/8 and F/11: The Median Apertures That Can Be Used to Shoot Anything
You can safely use f/8 and f/11 when taking pictures of groups of people as well as landscapes and cityscapes without compromising focus from front-to-back. In fact, a lot of landscape photographers use f/11 and sometimes f/8 at night. So when you’re feeling lazy and you’re really not fussed about what you are shooting, just use either one of these. Bear in mind though that these apertures are now getting small, so either your ISO setting or your shutter speed will increase. Use a tripod if you have a long shutter speed. Here are some examples at f/8 and f/11.
I’m not sure how good your monitor is but if you have a Macbook Pro or an iPad with a Retina Display or any other good large display with a high resolution, you should be able to appreciate how all the buildings are in sharp focus at f/8. I’ve hyperlinked the image to a bigger size – just click to view the larger image. It can be difficult to demonstrate the additional depth-of-field at these apertures without a powerful display, but if you try and shoot some images of groups of people standing behind one another or perhaps a cityscape like this one at f/8 or f/11 you’ll safely get everything/body in focus.
Here’s a night shot taken at f/8.
The bottom part of this image has been cropped because there were some undesired shadows which I could have dealt with in Photoshop using a different method other than cropping. However, this composition worked well and the image was almost in focus front-to-back with focus set to infinity. The camera was placed on the floor so the ground nearest to camera, the stones in the foreground and some of the grass is out-of-focus. However, you can see clearly that from the nearest tree to the farthest, the image is in focus.
This was a lazy shot because I just placed the camera on the floor shooting in Aperture Priority mode with an exposure compensation of +0.33 EV. I should have used a spider tripod and shot in Manual mode at ISO 50 to cut down on the noise reduction workflow in Camera Raw, but this is besides the point. The point is that f/8 works well as a landscape aperture at night.
Here’s another example with a slightly longer exposure that captures the tail lights of night-time traffic. We can explore longer exposures in the next section under shutter speed. You should be able to appreciate the sense of depth that can be achieved at f/8.
Here’ an example at f/11.
This image demonstrates how pretty much everything from front-to-back can be brought into complete focus at f/11. The tea leaves in the foreground to the left are in focus as well as the trees farthest away from the camera on the horizon.
Here’s a landscape image taken at f/11 outside the Houses of Parliament at night.
Focus is set to infinity to bring everything from from-to-back into focus – clearly f/11 can be used successfully as a landscape aperture. Big ben is in focus as well as the foreground. This was a single shot of approximately 5 minutes taken on Phase One digital back that has the ability to capture a scene with a wide dynamic range from shadows to highlights and since it’s such a large exposure time, look at how the camera has beautifully captured the colourful rays of light of the London bus to the right. The trees in the foreground identify themselves as wonderful partial silhouettes against the backlighting on the Houses of Parliament and the traffic.
So f/8 and f/11 can be used to shoot anything – a handy set of mid-range apertures.
Now … just for comparison, below are three identical images taken at f/11, f/16 and f/22. Take a careful look at all three.
Hopefully after carefully observing all three images you’ll notice that more of the leaves from front to back come into focus as we progress from f/11 to f/16 and onto f/22. And all that which is blurred in the background is least blurred in the f/22 image. Focus was set at 0.9 feet as opposed to infinity. The other thing to note is how placing the camera on the ground generates a strong sense of depth. Getting down to the level of the leaves as if I were a snail does so much for this picture.
As well as f/8 and f/11 I’ve also introduced f/16 and f/22 here without bringing much attention to these smallest apertures. There is a lot of discussion amongst photographers about avoiding the use of apertures f/16 and f/22 because they tend to generate a phenomenon call diffraction – that it, because these apertures are so small, the light that hits the edges of the aperture as it enters the lens tends to get diffracted from its normal path. This results in loss of sharpness.
Lens manufacturers will provide information on the sharpest aperture for a given lens and there are sites that provide reviews on lenses that include this sort of information. My advice is to not worry about diffraction at this stage. It’s not a major issue … trust me. When you really get into your photography and start to develop large prints, you’ll know what apertures work for you in terms of making the sharpest photographs for the lens you own. At this point, shoot at every aperture … even f/22, and then decide for yourself.
I tend to shoot my landscape images at f/11 on my manual camera, but I’m not afraid to shoot at f/16 and f/22. The secret to a sharp photograph is to use a cable release for the shutter (so you don’t have to touch the camera), a good quality sturdy tripod and to take the shot in “mirror up” mode. Every digital SLR has a mirror up mode so have a look at your camera manual to learn how to use it. Taking a photograph in this mode will allow you to flip the mirror up when you first press the shutter release button, but then you will have to press it again to release the shutter and take the photograph. The tripod, cable release and mirror up mode generate the least amount of camera shake delivering much sharper images. Please get into the habit of shooting like this, especially for your landscape images.
So far, you’ve learnt that the depth of field in a photograph can be controlled by the “size of the aperture” and if the “focal point” is varied, it can shift the out of focus areas forwards or backwards.
What we want to know now is …
Does the focal length of your lens affect the depth 0f field?
This is a difficult one to explain but the answer is No. Not if the size of the subject remains the same in each image taken at all focal lengths. You’d have to do this by moving back and forth depending on the focal length of the lens. This is really a matter of proving the point and The Luminous Landscape has an article titled “Do Wide Angle Lenses Really Have Greater Depth of Field than Telephotos?” which proves with visual evidence that depth of field is not affected by the focal length.
One thing that I would like to talk about here is reproduction ratio. Take a look at the image below.
This image has been taken with a 100mm lens with a Macro feature – macro photography is close-up photography of very small subjects such as insects where the size of subject on a finished print of size 6″ x 4″ is equal to or sometimes greater than life-size. There is a provision that needs to be met for this to happen. The lens used to take the photograph must have a reproduction ratio of 1:1 and it must be used on a full frame 35mm sensor (which has a size of 36mm x 24mm).
On your computer screen, the ants may look larger than life size. There are two reasons for this:
1. The dimensions of the image at twice the size of a 6″ x 4″ print – specifically the image dimensions are 12.5″ x 8.3″ with a resolution of 72 ppi, and
2. Your screen resolution in pixels per inch (ppi) and the size of your screen will also be a determining factor. For example, the image dimension in pixels is 900 x 600. The size of my display in inches is 13.13″ x 8.19″ and the resolution is set to 1440 x 900 ppi. This gives a screen resolution of approximately 109 ppi. Therefore, relatively this 12.5″ x 8.3″ at this screen resolution will appear as 8.26″ x 5.48″ because the ratio of image resolution (72 ppi) to the screen resolution (109 ppi) is 0.67 meaning that the image appears about two-thirds of its actual size.
This may have thrown you completely but don’t worry about it too much. The whole point of this discussion is that depth of field can appear to be different at a fixed aperture for two separate lenses of different focal lengths. Lenses with big focal lengths above 85mm (e.g. telephotos) have an acute field of view and naturally make subjects appear larger than wide angle lenses with focal lengths of 28mm or less.
This dramatically reduces the depth of field and requires focusing to be very accurate. Look how shallow the depth of field is in the macro picture of the ants. The other reason why I’ve touched on this concept of reproduction ratio is that in the images above, the focal length of the lenses used is not always the same for the purpose of demonstrating how depth of field changes with aperture setting. Different focal length have been used with subjects of different sizes so the results may look a little skewed. But I think you will have gotten the gist that more of the image from from-to-back comes into focus as aperture size decreases.
It would have been boring to shoot with the same focal length and the same subject and the same background varying only the aperture to show how depth of field changes.
Now that you know how the aperture affects the depth of field in a photograph …
How Can You Choose The Right Lens For The Job At Hand?
It’s frustrating for beginners and keen amateurs to decide which lenses to spend their money on. I know that the above information should hold you in good stead for making decisions when buying lenses and this part of the course is probably getting too long, but wait … don’t rush into buying lenses yet … stick to the one that came with your dslr camera and let me walk you through some important bits of information to help you make better buying decisions.
I personally will only recommend the most superior lenses regardless of price, but I may recommend some cheap lenses too if I think they are good starting point. My intention here is not to recommend individual lenses because I am not a lens expert. I’ve just bought lenses over the years and know which ones produce the best results for specific situations. There are good websites where you can read detailed reviews of lenses and online stores where you can buy them with complete confidence and trust. I will list them in the sidebar.
So here is a list of important things to consider before buying a lens:
1. Camera Sensor Format - before the digital age, photographers took pictures on film cameras and they were predominantly 35mm SLR film cameras. Have a look at the image below which demonstrates the sizes of sensors used on different camera systems today.
Notice that the 35mm sensor size is listed as the “full frame” sensor and has a crop factor of 1.00. This means that when you put any given lens on a full frame (be it a 35mm film or a digital SLR) camera, you will get to see the true angle of view that the lens is designed to provide when you look through the viewfinder.
For example, the Canon 50mm f/1.4 lens comes with a 46° angle of view and mounting this on a full frame camera will give you a 46° angle of view. However, the same lens mounted on … let’s say … a Canon DSLR with an APS-C format sensor will produce a more acute angle of view than 46°. When you look through the viewfinder, the field of view (FOV) will be cropped by a factor of 1.62. So the lens is behaving like a 50mm x1.62 = 81mm lens.
As a result, you will have to step back several feet to get that 46° angle of view and this is a compromise that you may not be willing to make. The sensor formats above that have a crop factor greater than 1.00 are what the different manufacturers use on their entry-level DSLRs, point-and-shoots and some of the new smaller cameras like the Sony NEX range that come with interchangeable lenses.
If money is not an issue for you, invest in a full frame digital SLR camera. However, if you’re on a tight budget and are happy to stick to an entry-level DSLR at this stage (and there is nothing wrong with that), you should because the lenses that come with these cameras will cope with this crop factor. To get a 46° angle of view on an APS-C sensor, you would simply have to use a focal length of 50mm ÷ 1.62 = 31mm. On an entry-level DSLR, you can achieve this with a zoom lens that encapsulates this focal length of 31mm in its zoom range. A common zoom lens on a lot of entry-level DSLRs is 18-55mm.
Having said this, the quality of these lenses is not great but then again it is not too bad either.
2. Prime Lens or Zoom Lens? - a prime lens is a fixed focal length lens. Should you have a prime lens in your collection, a zoom or both? I would definitely have a couple of prime lenses in your collection. If you have an entry-level DSLR, stick to the cheap zoom that came with it … it’ll do for now.
I shoot mainly with prime lenses now and rarely use a zoom lens. When I go outdoors to shoot landscapes be they in an urban area or in the rural outskirts, I take with me a 25mm, 40mm and 100mm prime.
A good reason to start shooting with a prime lens early on as a beginner is that it will …
… Train your eye!
As you now know, a prime lens has a fixed field of view … it can not change because the focal length is fixed. This has a major benefit – it will make you use your eyes to look for what will fit into that field of view … you’ll be required to think about your photograph … what you want inside that field of view … the frame. It’s not a case of shooting willy-nilly at anything zooming in and out in an uncontrolled fashion.
With a prime lens, you are required to think more about your framing … what goes inside the frame … what must not interfere in the frame from the edges. And this will require you to move around more because sometimes, a good photograph is made from a different angle and not necessarily from where you are standing. In time, you’ll know the field of view for each of your primes and you’ll pick up nice scenes to encapsulate inside those FOVs. Trust me on this, a prime lens will train you to become a better photographer. It will train your eye. Photography is an art that requires you to visualise and deliver emotions in your photographs.
Here is a photograph I took with a Carl Zeiss Planar ZS 50mm f/1.4 prime lens. I wanted my wife to the right of the frame from head to toe parallel to the bright light on the left.
I asked my wife to walk down the staircase slowly holding the rail and let her know that I would take the shot when she were parallel to the tube of lighting to the left of the frame. I wanted her to walk because I wanted one leg behind the other – I felt this would be a more interesting shot than her merely standing on one step.
I stepped back far enough to make sure she fit into the frame from head to toe, focused manually at my chosen aperture since this was a fully manual lens. I had to get my exposure right first with the flash gun in manual mode and once I was happy with the exposure, she walked down and I took 5 shots and this one was perfect.
Manual lenses can be difficult to work with when shooting moving subjects, but like anything … with practice it becomes second nature. Since then Zeiss have released the ZE series of lenses which come with fully automatic metering so life is so much easier now.
Zoom lenses in my opinion are for wedding photographers – these guys don’t have time on their side and can not waste what time they do have moving around with a prime or asking their human subjects to move around. However, they do use primes when photographing the bride and groom alone. They will be more obedient because it their big day and they want the best shots possible. This is when those big aperture lenses like the 50mm and 85mm f/1.2s come out of the bag.
It is now 2012 and there are very high quality zoom lenses out there so there is no harm in owning one. However, primes are a must. You can get yourself some very good prime lenses for cheap as chips and you’ll be taking some amazing shots with them.
The Canon f/1.8s are amazing and will cost you less than £100. A high quality L Series Canon Zoom can cost you anywhere in the region of £500-1500. Don’t buy a zoom yet … stick to the one that came with your kit.
3. Which Focal Lengths Should You Buy? - regardless of whether you have a full frame camera or not, get yourself a 50mm and a 100mm prime lens. If you don’t a full frame yet, you may own one in the future. Below the 50mm focal length, I would advise you to use the zoom that came with your kit if that is the case. Most SLR kits come with a zoom with a focal length range of 18-55mm. A Canon full-frame often comes with their 24-105mm f/4 L Series lens.
You can buy a 50mm prime lens either as an f/1.8 or an f/1.4. The f/1.4 will be more expensive and if you can afford it then go for it. That f/1.4 will create a nicer bokeh than the f/1.8.
Here are some of my favourite lenses that I can comfortably recommend because I have used them personally.
2. Canon 100mm f/2.8 USM Macro Lens is an amazing lens. It is simply amazing. Some of the images on this page have been taken with this lens – please check the image captions. I take this lens out with me all the time along with my Canon 40mm f/2.8 Pancake lens. The good thing about this lens is that it comes with a macro feature and can also be used as a portrait lens. It focuses extremely fast. You can buy it at Amazon.co.uk or Amazon.com.
3. Carl Zeiss Planar 50mm f/1.4 ZE Lens is my favourite lens. It is a manual focus lens so it will not autofocus. However, the quality of the glass is superior and the lens body itself is made of metal. It is a solid lens with excellent resolving power which will bring out the amazing colours in your photographs. This lens is also available in the ZF fit for Nikon SLRs and the ZK fit for Pentax SLRs. You can buy it at Amazon.co.uk or Amazon.com.
This is a sufficient list to consider if you are a Canon user. I apologise to users of other brands of SLRs cameras but I am just not familiar with the quality of those lenses so I can not make suggestions for you.