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009 - Aperture and Depth of Field

In previous posts I have written about the fact that aperture has an affect on the depth of field, but as usual that is only a part of the equation.  First of all let's just be clear about what I am meaning by depth of field. In layman's terms I am meaning the distance between the nearest point with good focus to the furthest point with good focus. Anything in front of the nearest point or behind the furthest point would become blurred and the further in front or behind would be more blurred. If you read more advanced descriptions it will talk about the circle of confusion and acceptable sharpness and other technical terms but basically it's what part of the image is sharp or blurry.

The other factors that also determine the depth of field are the focal length of the lens and focus distance.  I tried to cover focal length in my previous post so you could refer back to there if you need a refresher. I don't believe I've mentioned the focal distance before but approximately this is the distance from the camera to where the focus is at its sharpest. This is the point where when you are using autofocus that the camera has determined to be the best distance for a good photograph.  If you are taking a portrait photograph you would want the camera to focus on the face and more specifically on the eye(s) if they are visible. In a landscape photograph you would probably want the focus distance to be on the main subject in the landscape.  I will cover focus distance a bit more in a later post.

As there are three main factors which affect depth of field I think it might be best to remove one of those factors to make it a bit simpler to illustrate. So for the remainder of this post I will concentrate on aperture, focus distance and depth of field on my trusty 50mm fixed focal length lens. Another factor is the sensor size and my camera is a cropped sensor with a crop factor of 1.6 so any figures I report will be for this camera unless I state otherwise.

As I have mentioned previously, when you are taking a image the wider aperture will let in more light but will reduce the depth of field.  In a portrait photograph this may be the effect you want where the face is in sharp focus but the background is blurred so that it simplifies the image to concentrate on the main subject. Calculating the depth of field is complicated but there are plenty of calculators about which will work it out for you. I use a application on my iPod Touch (PhotoCalc) which is very easy to use and also has lots of other useful information.

I'll use a real world example to illustrate depth of field for a portrait. Let us say that the model is 5 feet (approx. 1.5 meters) from the camera and the aperture is set to f2.8 then the depth of field would be from 4 foot 10 inches to 5 foot 2 inches or 4 inches (100mm) in total.  Not much really, that's from the end of my nose to the front of my ear assuming the camera focuses at 5 feet. If the camera focuses on the end of my nose then my eyes could be a bit blurred with having such a big nose. If I set my camera to portrait picture style it was tending to set the aperture to f4 which gives me an extra 2 inches of depth of field which is a more realistic 6 inches (150mm) when using auto focus.

Now if you have the model a bit further away so you get more of them in the frame the figures are a bit different. Lets say the model is 8 feet (approx. 2.5 meters) from the camera then the aperture is set to f2.8 the depth of field becomes 10 inches (250mm) and at f4 increases to 14 inches (350mm). At the bigger distance you will get more of the model in focus and start getting the background in focus if it is near to the model.

If you are wanting the background in focus then you might want to stop the aperture down a bit further. In the automatic modes this might be where you change from portrait style to fully automatic to even landscape picture style. With the model still at 8 feet from the camera f5.6 will give 1 foot 8 inches (500mm) depth of field and f8 will get you 2 feet 5 inches (nearly 750mm).

If you have good eye sight and want to switch your lens to manual focus you could reduce the depth of field even more my opening up the aperture even more. This could enable you to make an image where only the eyes are in focus and the rest of the face becomes a little blurry (very artistic).  You would have to be in one of the creative modes rather than the automatic ones because the portrait picture style on my camera doesn't go to those lengths. Creative modes are for later posts when we start to find the automatic modes a bit too restrictive.

What about real world examples for landscape photography. Generally the aim here is to get as much of the scene in reasonable focus. Say we're in a woods and furthest distance you can see is about 65 feet (20 meters) and the nearest object of any size is 16 feet (5 meters) and there's plenty of light. Assuming the camera will focus on the nearest object then at f8 you would get about 10 feet (3 meters) in depth of field from about 12 feet to 22 feet or 4 foot in front of the subject to 6 feet behind. At f11the depth of field goes up to 15 feet and at f14 jumps up to 22 feet with about 6 feet in front 16 feet behind.

None of these are going to everything in focus and you may be running out of light if you close the aperture down any more. So what is the answer? As usual it's a compromise. The first thing to ask is how much you actually need in focus? Is there anything in front of the main subject you're really bothered about and how much detail do you need in the background?

 Let's say there is nothing in front of the main subject, so you could focus a bit further back into the scene to gain a bit more sharpness in the background. If you were to set the aperture back to f11 and then focus to 25 feet, the near limit for the depth of field would be about 15 foot and the far limit would be almost 70 foot. This would get your whole scene in reasonable focus although your main subject may not be as sharp as it could be. To move the focus to a different distance you could either focus manually or point the camera to an object further back, half press the shutter and then recompose.

Last example for this post. Another landscape scenario where you're on the top of a hill and you can see for miles. The nearest object of any size is 100 feet (30 meters) away and your aperture is set to f11. Now if the camera focuses on that nearest object then the near limit is about 30 feet but the far limit is out to infinity.  However there are parts of the scene which are closer that 30 feet which are going to be blurry and maybe you wouldn't mind being a bit sharper.

One option would be to use the hyperfocal distance which is simply the nearest point at which the far limit is infinity. On my calculator app. this is 39 feet 3 inches which gives a near limit around 20 foot. Maybe this is fine but perhaps you want just a bit more sharpness in the foreground. You could focus a bit closer but then you're going to lose the sharpness in the distance. It would probably be better to shut down the aperture to say f14 where the hyperfocal distance becomes around 30 feet with the near limit down to 15 foot. You might think about closing the aperture further but you can then hit problems with diffraction which will counteract the extra depth of field by making the whole image less sharp. All lenses are different but I would tend to make my limit f16.

There's a lot of numbers in this post and it's a bit long so I apologise for any confusion that combination may cause.  In summary for portraits you would probably want to have a wide aperture to reduce the depth of field and for landscapes you would tend to use a smaller aperture to increase the depth of field.  The focusing distance can make a big difference for both portraits and landscapes where generally the bigger the focus distance the greater the depth of field.

Next time let's add in the focal length dimension into the mix and see how that affects the depth of field.

008 - Focal Length

Last time I said that I was going to talk about aperture settings next but then it occurred to me that the focal length has a bearing on the aperture setting so I had better cover the focal length first. Simplistically I guess the Focal Length can be thought of as a measure of the magnification where 50mm is somewhere around the base line which is why it is classed as normal. If the focal length is less than 50mm then it is effectively a negative magnification where things start looking further away or smaller and if the focal length is above 50mm then things will look closer or bigger.

The normal range is anything from around 35mm up to say 70mm where you have a bit of positive and negative magnification around normal.  So when the focal length is below the normal range we're considering this to be wide angle, down to 10mm or even 8mm where we are at a very wide angle. Above normal we start at short telephoto up to around 120mm or 150mm, then long telephoto around 200mm to 300mm and above that we're into super telephoto territory.

If you have a DSLR you may well have had a kit lens in the package that you bought and these tend to be somewhere around 17mm or 18mm up to 55mm or 85mm. If your DSLR has a cropped sensor then you will need to apply the crop factor to the focal lengths on the lens to get the equivalent full frame focal length. A cropped sensor is one that is smaller than a full frame or 35mm sensor and will be what you'll find in most 'prosumer' cameras (i.e. non professional cameras).  The crop factor is usually about 1.5 or 1.6 so an 18mm to 55mm lens becomes 27mm to 82.5mm when the crop factor is 1.5. That makes the camera and lens goes just a bit either side of the normal range so is classed as a normal zoom. Some kit lenses do go a bit longer and reach well into the short telephoto range. Also the four thirds standard cameras have a crop factor of 2.0 which means you'd need to double the focal range marked on the lens.

Why have a cropped sensor? Well a cropped sensor camera start off as far cheaper than professional cameras and can use smaller and less expensive lenses. The price of the cropped sensor cameras start around £300 and can go right up to almost as much as a full frame camera which you'd be expecting to pay well over £1,000 for the body only and anything above that.

If you have a compact or point and shoot camera the focal length range will be something similar to the DSLR with the normal kit lens. That is starting at somewhere around 24mm to 28mm and going up to anything around 3 to 7 times zoom or about 75mm to 200mm as equivalent to a full frame DSLR.

In general you would be using a wide angle where you were wanting to get a lot of the scene into the frame or where your not able to stand far away from a large object that you were trying to photograph.  This would be mainly wide panoramic landscape shots or maybe architectural images. A problem you may find with wide angle shots is the tendency to get distortion, particularly towards the edges and also if pointing the camera upwards or downwards. Things close up also tend to look disproportionately large to taking portraits with wide angles would tend to make the subjects nose look quite large. Perhaps not a good idea for serious photographs but could be used for fun shots.

Photographs taken in the normal range are just that, they would be how you would normally see them. This is why kit lenses are favourite as a starting point for your photography because it can be used for all types of photographs.  Even now, when I have four other lenses in my bag, I will use the kit lens for about 75% of my shots because of the versatility. I take mainly landscape shots but the lens is well capable of good portraits and it is even quite good for close up photography.

The short telephoto range is good for getting closer when you can't physically get closer to your subject or want to stay a little further back. For example taking photos where there is some barrier to getting closer or if you taking people photos when you don't want to invade their personal space.

The longer telephoto ranges are used when you can't get anywhere near your subject. So this would be where things are very far away or very small (or a bit of both). The obvious use would be wildlife where generally, in the wild, the subject doesn't tend to come close up to you, or maybe you don't want to get too close to the subject.

These uses are, as usual, not hard and fast rules so you can mix it up a bit to make the images you want. I hope this post has been useful and next time I will definitely get onto aperture settings and depth of field, promise.

007 - Exposure For Beginners

So finally we get to looking at exposure.  I've been putting it of for a while because I wasn't too sure where to start. Let's try looking at it from this angle, a camera needs light hitting the sensor to be able to record what it can see through the lens. Depending on where you are, what time of day it is, the weather conditions or the lighting conditions if you are inside there will be differing amounts of light available to the camera. The camera needs a certain amount of light hitting the sensor to produce an acceptable image and this is the exposure.

Given that in these differing amounts of available light the camera wants to get sufficient amount of light to get a good exposure, how does the camera control the amount of light? I think in my previous posts I've hinted at some of the ways this is done but essentially it uses what is termed the exposure triangle. The three things the camera can use are the aperture size, the shutter speed and the sensitivity.

The aperture is how far open the lens makes the hole that it lets the light into the camera which it controls using the aperture blades. A tiny aperture will obviously let less light in than a wide aperture, but the aperture also controls the depth of field, or in other terms. how much of the scene is in focus. A small aperture will give a wide depth of field and a large aperture will give a narrow depth of field. As we have discussed in earlier posts we would most likely want a wide depth of field for landscapes and probably a narrower depth of field for portraits.

The shutter speed is simply how long the shutter stays open and it follows that the longer it is open, the more light it lets in. For action shots we would probably want the aperture to stay open a very short length of time to freeze the action. For normal hand held photos we would want the shutter speed to be fast enough to prevent camera shake. If we're using a tripod the shutter speed is less important unless there is movement in the scene we're trying to capture. Sometimes we actually might want the shutter speed to be very slow so that we would purposely blur moving objects or scenes and we will discuss this in a later post.

The sensitivity or ISO setting is how much the camera will in effect amplify the light that is picked up by the sensor. Generally we would want this to be fairly low because as the sensitivity is turned up there is the possibility of the image being adversely affected. Particularly in the darker parts of the scene you might start seeing flecks of light or colour appearing and this is usually termed as noise. I guess it's similar to cranking up you stereo system and getting a buzzing noise through the speakers.

So to get the correct amount of light into the camera it will determine how much available light is present and then balance these three variables to get the correct amount for a good exposure. How it does the balancing act will depend on the type of picture you are taking. The actual setting it uses will depend greatly on the amount of available light. If it is very bright the camera has an easier job because it can use the ideal settings for the type of picture.  However if there is a shortage of available light it will probably need to make some compromises or more than likely try to use the flash to compliment the available light.

For a portrait the camera will open up the aperture to get the narrow depth of field, then it will make the shutter speed fast enough to cut out camera shake and finally will adjust the sensitivity if necessary. If there is too much available light the camera may reduce the aperture from the ideal setting, reduce the sensitivity to the minimum and then use a faster shutter speed than necessary to cut down the amount of light hitting the sensor. If there is insufficient light and the flash is turned off the camera may open the aperture a little more than ideal, then increase the sensitivity as much as it dare and then set the shutter speed to as slow as it needs. Sometimes this can be too slow and you might start to see motion blur from camera shake or the movement of the subject.  If it's too dark the camera may be unable to focus or may refuse to fire a shot when you press the button.

For a landscape the camera will close down the aperture to get the wide depth of field, it will probably need to reduce the shutter speed to compensate for the smaller aperture and will try to keep the sensitivity low. As with portraits, if there is plenty of light there is usually no problem with getting the ideal settings but if the light is poor then compromises need to be made. The aperture will need to be opened up a bit, the shutter speed slowed down and possibly increase the sensitivity.

I think I need to discuss exposure a little more in the future, but I think this post has gone far enough.  I hope I have been clear and that I haven't confused anyone. If you have any questions, please leave a comment or send me an email and I'll try to answer. Next time I think I will go into more detail about the relationship between aperture size and depth of field.

006 - Testing Picture Styles

Following on from my previous post I decided to do some testing of the picture styles over the weekend just to confirm what I had written. It was a bit of a dull overcast day so I thought the best way to do the testing was to use my fairly fast f1.8, 50mm fixed focal length lens to give the camera chance to open up the aperture to get in more light.

Now I have no intention in this blog to concentrate on equipment at all but I would urge every beginner with a DSLR to get a fast 50mm lens because they are very versatile, even though there's no zoom, and they are very cheap. My Canon lens is £75 at Amazon, UK or around $100 in Amazon, USA, which does mean we're paying extra in the UK as usual but it's still a bargain. The build quality isn't that great but if it breaks it's cheap to replace. The Nikon 50mm f1.8 is slightly more expensive and both companies also make and f1.4 and Canon make an f1.2 but these are not so cheap and probably not worth it unless you're a professional. In a later post I will probably go back to look at things you can do with this lens and I will link forward from here when I have posted.

Anyhow back to the testing. The method, not very scientific, was to find a place to stand and then take a shot of the same scene using each of the picture style settings in turn. The first place I stood was in a old lane under the trees so it was even darker than out in the open and the camera would have to work to get enough light. On the fully automatic setting the camera opened the aperture a bit, increased the sensitivity and used a fairly fast shutter speed. In portrait mode the camera opened the aperture to almost fully wide open as expected, dropped the sensitivity back down and had a slightly slower shutter speed. In landscape mode the camera closed down the aperture to get the wider depth of field, put the sensitivity back up and dropped the shutter speed down to the minimum for the focal length. Interestingly in macro mode the aperture was between what the camera had set for landscape and portrait.  I guess the camera was after a medium depth of field which makes sense I suppose because if you're taking a macro shot you probably need a bit more depth of field than for a portrait. On the sports or action mode the camera opened the aperture up wide again and increased the sensitivity so that it could set a faster shutter speed.

On my second set of shots I was out in the open and taking shots of a tree with the murky sky behind. This time the fully automatic mode closed down the aperture a bit more than before, had the same sensitivity and had a much faster shutter speed. The portrait mode again opened the aperture to almost fully open, dropped the sensitivity again but this time had an even faster shutter speed. In landscape mode the aperture was the same as in the fully automatic mode but this time the sensitivity was reduced and also the shutter speed. The macro setting had the same aperture as before, dropped the sensitivity slightly and also had a faster shutter speed.  In the sports mode the aperture was the same as for macro but the sensitivity and shutter speed were higher.

Overall I believe that this more or less agrees with what I wrote last time except that I didn't think there would be much difference between portrait and macro modes. On reflection I can understand why the macro settings would want a greater depth of field so that's something I have learnt. The one thing that I did find interesting was how in the second set of tests the camera seemed to keep the aperture and sensitivity settings fairly similar to the first set but increased the shutter speed quite significantly. I'm not entirely sure that I agree with this approach and I will discuss this in the next post when I start to cover exposure.

One last set of tests were straight comparisons between portrait and macro modes when taking a close up of some holly berries. Strangely in the test shots that I took the camera used exactly the same settings for each shot in both portrait and macro modes. This threw me to begin with but then I realised that in the portrait mode the camera had determined that the subject was very close and therefore decided to increase the depth of field. I said that the camera was very good at recognising the situations and adjusting the settings to suit. 

I think that in conclusion I'm very impressed with how my camera used not only the picture mode that I have chosen but also everything else it can deduce from the scene when it makes its settings. As I keep saying the next post will be starting to look at exposure and hopefully this will help to explain a bit more about the settings that the camera decides upon.

005 - Picture Style Settings

So far I've suggested that starting with the camera set to fully automatic because most of the time it can decide what sort of picture you are taking and make the correct camera settings. But what if it doesn't get it right for some reason, maybe you're taking a landscape photo but there's something close by in the middle which fools the camera into deciding that you're making a portrait. What you will end up with is an image where the close by object is in focus but the landscape you were trying to capture is all out of focus. What you might want to do is to take a little more control of the camera by using the picture style settings.

Most modern cameras will have a set of picture styles that you may choose which tell the camera they type of picture you are wanting to make. On my camera there is a dial on the top but sometimes you might have to use buttons on the back or select from a menu on the screen. You will need to check with you're camera manual if it isn't too obvious. Cameras will have a different set of picture styles so I will go through the ones that are on mine and hopefully your camera will have most of the same and maybe others.

The first couple of picture styles are those I mentioned last time so I will discuss them briefly. Firstly 'Portrait' which, as I wrote last time, will typically have a narrow depth of field to isolate the portrait subject and a fairly fast shutter speed to cut down on camera shake or movement by the subject. On my camera the little icon on the dial looks a bit like a head which seems to make sense but of course you could use it for still life too. The camera may want you to use flash to put a bit of extra light on your main subject but you may be able to switch that off if you don't want it.

Secondly is 'Landscape' where you are probably wanting to get most (or all) of the image in focus. Here the camera is setting a wide depth of field and the shutter speed probably is less important because landscapes tend to have less movement in them and you may also be using the wider end of the zoom where you can get away with slower shutter speeds. The camera shouldn't select the flash as the effective distance of the flash is only a few feet however it may choose flash to add a bit of light to the nearest objects. Again you may need to refer to your camera manual if you want to enable or disable the flash. On my camera the icon on the dial looks a bit like some mountains and a cloud.

The next setting on my camera is 'Macro' which I must admit I wasn't too sure how this would be that different from 'Portrait'. Again you'll probably be wanting a fairly narrow depth of field and a fairly fast shutter speed to cut down on shake. I looked in my camera manual and it didn't really enlighten me any. I will do some investigation with this setting at the weekend and may update this post if I find out anything useful.

Next is the 'Moving Subjects' setting which has an icon that looks a bit like someone running. I think that this is one that maybe the automatic setting is likely to struggle with because it may not be able to identify that the subject you aiming capture is moving. You would typically use this setting for photographing sport or anywhere else where you want to freeze the movement of the subject. The main camera setting for this would be to have as fast a shutter speed as possible and have a reasonable depth of field. On my camera it also sets the auto focus to track the subject by refocussing between every shot in case the subject is moving towards or away from you. The sensors sensitivity may need to be increased and the camera may also tend to use the flash if there is a shortage of light.

The final picture style setting is 'Night Portrait' which on my camera has an icon that looks like a head and shoulders with a star in the background. This will also be similar the 'Portrait' setting but as it's for night portraits it will probably always use the flash. For a night portrait you should have the subject fairly close so that the flash will be able to reach and you will probably need to use a tripod to cut out camera shake.

I do have another setting on this end of the camera dial but this is purely for setting the flash to disabled without having to use the menus. Apart from that I believe it just acts the same as fully automatic. You would want to use this setting in museums or sports arenas where flash is either forbidden or wouldn't make any difference to the lighting.

So you can use these picture style setting when you want to either help the camera out or perhaps take more control of the camera. There's nothing to stop you using the portrait setting for landscapes if you only wanted the main subject in focus and wanted to make the foreground and background blurred. Or you could take a portrait using the landscape setting if you were wanting the background to stay in focus. However I suspect that if you were wanting to make these artistic decisions then you'd probably want to have a lot more control but we won't be getting to that stage for a while yet in this blog.

Next time we're going to get a little more technical and start talking about light and exposure. I'm not too sure at the moment how to start slowly in tackling this subject so the next post will be a surprise to all of us.

004 - Introduction to Image Types

Way back in the first part I mentioned that when the camera is set on fully automatic it would choose an image type depending on what it could detect in the frame. At the time I purposely didn't elaborate on what those image types might be because I was assuming that the camera would not be too far of the mark for a beginner. However, now we've got to part four so I thought it time to put forward my understanding of the basic image types may be and how the camera will use different settings.

Firstly let's consider making a portrait of a person.  What the camera would detect in the frame would be an large object quite close and fairly central with space around it. The camera determines this information about the scene while auto focusing the lens. The camera would also detect a similar scenario if you were taking a still life of a vase of flowers or a bowl of fruit. Perhaps even if you were in the open taking the picture of a statue or some other object with space around it. In any of these cases the camera would use the information and compare it to similar scenarios in its database and come up with some settings for the picture. It all happens very quickly so there's no need to wait for it to get itself ready.

What setting will the camera use for what it detects as a portrait image type. Well generally you will want the photo to concentrate on the main subject and one way of doing this is to simplify everything else. The standard method is make the background a little blurry by throwing it out of focus. The main subject needs to be sharp and clear but the rest of the frame is less important. The technical term for this is having a narrow or small depth of field and I will discuss this and how to achieve it in a later post. The other important thing to keep the sharpness is a fairly fast shutter speed to cut down on both movement of the camera or the subject if it is a person.

Sorry to inflict this image on you but I thought it might be useful to illustrate the previous paragraph. I just took this self portrait using fully automatic mode and the camera has correctly identified this as a portrait type of picture. The only part of the picture that is in focus is from the end of my nose to just about my eyes, my ears and shoulders are getting a bit blurred, this is only about 2 inches (Ideally the focus should be on my eyes but the camera appears to have focussed on the end of my nose so my eyes aren't as sharp as they could be. I guess the camera has done the best it could and the photographer would need to take a bit more control to get it perfect. We've a long way to go to get to that stage but overall I think I'm quite happy with the result)  The blue vertical blinds behind me are completely out of focus and even looking closely you can barely make out the gap lines between the individual blinds. The shutter speed isn't as fast as it could be but it's nearly midnight so the lights are on in my study and you can see the on camera flash has kicked in fill the light in my face.

Next consider a classic landscape photo. During auto focusing the camera will detect nothing or very little too close and most of the scene way out into the distance. Again it will look for similar scenarios in its database and determine the best settings for the picture. I've not put it to the test as yet but I suspect there are a range of landscape settings that the camera could use.

This time the camera will try to keep as much of the frame in focus by using a wide or large depth of field. If there are objects fairly close by it will try to ensure that they are in sharp focus otherwise it will probably set the centre of the focus around a third of the way into the scene.This is a very approximate rule of thumb but worth remembering as you take more control of the camera. The shutter speed is less important in landscape photographs but must still be fast enough to reduce any blurring from the camera moving. The camera is unlikely to use the flash for landscape photographs as the range of the flash is only a few feet so wouldn't have a great deal of impact, however you may need to switch off auto flash the camera is trying to use it when you don't want it to.

Portraits and landscapes are the either end of the scale so there are lots of places in between. The camera will try to determine what you are photographing and will try to use the most appropriate settings however sometimes it's going to need some help. Next time I'll look at moving away from the fully automatic setting and helping the camera by choosing the image type or picture style you want.