depth of field
I responded to a question the other night asking for some guidance on Depth of Field and if possible an article. I thought about this for a while and it’s quite a complex subject involving ideas such as circle of confusion and hyperfocal focusing. Personally I don’t like complexity as it tends not to be that practical in the real world. Here then is my Lightweight guide to depth of field with a Micro 43 camera.
The first thing to realise is that Depth of Field is something completely different to lens sharpness. Sharpness is about how well defined edges appear in your image. Lots of things can contribute to an image being sharp or not. Camera shake will detract from sharpness as will vibrations. Unfortunately the aperture also contributes to sharpness which is possibly why people sometimes become confused.
When a lens is wide open at its maximum aperture e.g. f/1.8 it is unlikely that it will produce its sharpest results. Whilst high quality lenses will perform well when wide open, most lenses achieve their best results when stopped down around 2 stops from wide open. My experience with Micro 43 lenses is that they usually perform well when wide open and achieve excellent results when stopped down by around 1 stop from the maximum.
Stop a lens down to the other extreme and you will see the effects of diffraction creep in. This is where the light entering the lens diffracts on the blades of the aperture. This causes it to spread and the image becomes softer. Different lenses will start to suffer from diffraction at different apertures so I can’t give you any guidance other than to say test your lenses.
Now for depth of field. The first thing to realise is that there is only one point of true focus in an image. The further you move from this point the more the focus deteriorates. Near to the point of focus you probably don’t notice this but further away the image starts to appear blurred and out of focus. The area that appears in focus to the eye is the zone of acceptable focus; remember it’s not actually in focus, only the point of focus is in true focus.
The acceptable zone of focus extends beyond the point of focus and also in front of the point of focus. This is said to be the depth of field. How far this zone extends is determined by a number of factors which include:
- The size of the sensor – the smaller the sensor the greater the depth of field at a given aperture. Micro 43 is therefore good if you want lots of depth of field. Generally speaking you can’t do anything about sensor size unless you change camera.
- The distance of the point of focus from the camera – the nearer the point of focus to the sensor then the less the depth of field.
- The aperture – a smaller aperture will produce a greater depth of field than a larger aperture on the same lens assuming the other factors are constant. Take care however as you could make the aperture so small that the lens suffers from diffraction. There is therefore a balancing act between depth of field and optimum aperture.
- The focal length of the lens – Now all you science types don’t all cry out saying there is no difference it’s just down to compression and magnification (ignore this comment if you don’t know what I am talking about). Remember, this is the simple approach to depth of field. The wider the focal length of the lens then the greater the apparent depth of field that can be achieved, all other things being equal. Putting this in simple terms, take a picture with a 14mm lens and take the same picture with the same aperture and focus point using a 45mm lens and the 14mm will appear to have a greater depth of field.
The final key piece of information is that the depth of field extends roughly twice as far beyond the camera as in front of it.
So, how to use this assuming you want to create a large depth of field from the foreground to the distance:
- By the time you are about 50m away from the camera, you will effectively have reached infinity focus on your lens. Remember, this is a practical real world simplified guide.
- Select a lens that will allow you to create the composition you want.
- Estimate how far the nearest point to you (in the frame) is.
- Estimate how far 1/3 of the distance is from this point to 50m and identify something around that point in the frame. This is where you should pick your point of focus. Don’t leave this up to the camera to decide.
- Select an aperture that gives you the depth of field you need. Until you are adept at judging this you may need to take a few shots and check them at 100% magnification on the back of your camera.
- When you check shots the foreground is more important to judge than the distance. The foreground will show up areas that are out of focus much more than the distant hills.
- If you find your image is slightly out of focus in the foreground but the hills are fine you need to move the point of focus nearer to you.
- If the hills are blurred but the distance is fine you might need to move the point of focus away from your OR use a smaller aperture. Try both.
- Try to keep the aperture within the range for optimum sharpness.
All this might sound like a lot to remember but after a while it becomes second nature. I tend to shoot landscapes with a 14mm lens set to f/8.0. I know when the focus point is well selected this will give me good depth of field on most of my compositions. Selecting the focus point becomes automatic for me based on years of experience gained by taking a picture and checking the results.
Hope this helps.
I recently posted an article discussing how micro 4/3 cameras could achieve good depth of field at relatively wide apertures. This also stressed how the common advice to stop down the lens to a small aperture was misleading and probably resulted in poor lens performance and loss of image sharpness. Well, now it’s the turn of the LX5.
The LX5 is a compact camera with an oversized sensor and a great Leica lens that’s the equivalent of a 24-90mm lens on a full frame camera. Despite its oversized sensor, this is still much smaller than the Micro 4/3 cameras, which gives the LX5 a much greater depth of field at the same aperture.
I can only describe the lens on the LX5 as extraordinary in terms of sharpness and its ability to resolve detail, even in distant subjects. It has an aperture of f/2.0 at its widest to f/8.0 at the smallest. The f/2.0 can only be achieved with the lens set to the equivalent of 24mm. At the other end of the zoom range the widest aperture is f/3.5.
From my observations when using the LX5, the camera produces good images at any aperture and is certainly usable wide open (f/2.0). If I stop the lens down it start to hit its sweet spot by f/2.8 and performance begins to drop off after f/4.5. The question then, is how much depth of field do you get with f/2.8 and the lens set to 24mm (I am assuming here that you like I spend most of your time photographing landscapes)
To answer this question I am not going to resort to a depth of field phone app as I did before, but use a feature built into the LX5 which not only shows me the depth of field but allows me to set the hyperfocal distance. In case you’re not familiar with the term hyperfocal distance, this is the theoretical focus point that gives the maximum depth of field for your aperture/lens right the way to infinity. Here are the steps:
- Select the Aperture Priority mode (A) on the top dial of the camera.
- Switch the camera to manual focus using the switch on the side of the lens. When you are in Manual Focus, MF will appear in the bottom right of the screen.
- Press the rear adjustment dial on the back of the camera (top right) until the MF is highlighted. This is the dial that allows you to adjust the aperture and if you keep pressing it in you will cycle through aperture adjustment, exposure compensation and manual focus settings.
- Rotate the dial to the left and right. As you do this you will see a depth of field guide appear on the bottom of the camera screen with a solid yellow line that moves left and right. This line represents the zone of focus at the aperture and focus length selected.
- Move the dial left and right until the yellow line just touches infinite focus on the right hand side. You have now set the focus to give the maximum depth of field at your aperture and focal length.
To give you some idea of how much depth of field you can achieve at 24mm and f/2.8, you will find the closest point in focus is just over a meter away and the zone of sharp focus extends to infinity. Now the other benefit of shooting at f/2.8 is that you will achieve a very fast shutter speed and can hand hold even in poor light as well as reduce the risk of camera shake.
By way of an example, the night shot above was taken from the top of the Empire State Building hand held using ISO200 and f/2.8. Its pin sharp and prints beautifully at A3+. I have even passed it off at various presentations around the UK as being shot with a 5D MKII. I do always own up later as its great fun to see people’s faces when they realise it was shot with a compact camera.
I am growing tired of seeing the same advice trotted out time and time again about Landscape Photography. The advice that has me so wound up is that “if you want to get a full depth of field you need to use a very small aperture”. This advice has almost been carved in tablets of stone for all to see. Does it work; yes it does BUT IT ISN’T THE BEST ADVICE.
To me, this advice is almost the lazy way to photograph landscapes. The advice you should be getting is to shoot your landscape with the best aperture (the one that gives you the highest quality image) whilst still giving you the required depth of field. To understand why and why this is so important for Micro 4/3 and compact camera photographers you need to understand a few basics about lenses and depth of field.
Firstly most consumer lenses are designed to achieve their sharpest images and resolve the most detail when the aperture is closed down about 2 stops from wide open. For many lenses this means you will get the best results at around f/8 to f/12. Either side of this range you will find the image just isn’t as sharp and if you stop down the lens to around f/22 you might find all sorts of distortions can kick in. Buy the best lenses you can and you might see some improvement on this.
Now the thing with Micro 4/3 cameras is they seem to hit their best performance when stopped down just a little bit and the best way to understand this is by testing your own lenses. I haven’t done extensive testing but with my 14-45mm lens, I tend to shoot landscapes at between f/5.6 and f/7.1 for the 14mm end of the zoom range. I have found that if I stop down to f/8 or beyond then it’s not quite as sharp.
So you know the aperture range where your lens performs best, how do you ensure there is sufficient depth of field? The answer is by selecting the correct point of focus first and then selecting the correct aperture in this range. This is probably best explained with an example.
Suppose you find a nice landscape scene and there is a lovely rock that you want to place in the foreground. You compose the shot with your camera mounted on your tripod at just below eye height and the rock is about 5 feet from where you are stood. The distance from your camera to the rock is probably going to be about 7 feet. If I consult my depth of field chart (it’s actually an app on my phone) I find that focussing on the rock with my lens set to 14mm (on the GX1) the widest aperture that allows me to achieve infinite depth of field is f/6.3 – yes you read that right. The nearest point to me that is in focus is actually only 3.4 feet away.
Taking a more extreme example lets lower our tripod and move in close to the rock so that it looms large in our viewfinder. Unfortunately the 14mm lens isn’t wide enough so we move the Olympus 9-18mm set to 10mm. This is the equivalent of a 20mm lens on a full frame camera. Having moved in close we find our point of focus on the rock is just 4 feet from the camera. Looking at my depth of field app I find that I can achieve infinite depth of field at just f/5.6 and the closest point in focus is just 1.9 feet from the camera. At this aperture my lens is going to be performing at its sharpest and resolve the maximum amount of detail. The images produced will be substantially better than if I had used a small aperture such as f/16. Just for fun I thought I would check the aperture I needed with my 5D and its f/11.
Do you think you think you have been selecting the best aperture for your work?
Last Thursday night I was presenting at Bolton Camera Club. It was a good evening with lots of discussion, especially when I pulled out the sample prints I had taken. A lot of the members looking at the prints made from my LX5 compact Camera were surprised by the not only the quality and detail displayed but the “relatively wide” aperture I had selected. The image above was shot at f/8.0 yet it’s sharp from front to back. My New York Skyline shown in an earlier post was shot at f/2.8 and everything is in focus, even viewed close up printed at A3+. The member of Bolton Camera Club are not however alone in this surprise as it’s something I experience often when talking to club members from all over.
Selecting the right aperture for a scene is something we tend to do automatically once we have been in photography for a while. Unfortunately the aperture selection in lightweight cameras might not be quite as you expect it and you could end up making choices that have a negative impact on your photographs. If you stop and think, there are only a couple of reasons why you might want to control your aperture:
- To control your depth of field
- To control your shutter speed (increase or decrease)
Now I’m going to be controversial and say the only reason you should be changing your aperture is the first one. The second option, to control your shutter speed is in fact a trade off from controlling your depth of field. If you disagree good (you have your own opinion) but stay with me and understand my argument. It might just change your perspective on photography.
So let’s deal with the “misconception” of using aperture to control shutter speed and why I argue against this. My reason is that it’s actually a relatively ineffective when used in this way. If you want to change the shutter speed for creative reasons (which should be your first priority) it will be because your current speed if either too slow to freeze action or it’s too fast to introduce creative blur and motion.
Let’s say I want to freeze motion so I open up my aperture as wide as I can. This will increase the shutter speed but at the expense of reducing the depth of field in the image, something I might not want. Often such a reduction in depth of field will affect the aesthetics of the image and will change it completely. A better option is to increase the ISO setting as this is more effective. It will introduce noise but you can always address noise if it becomes too great in other ways. Another solution which is often overlooked is to use flash to help freeze motion. In the end you might need to adjust the aperture as well as these solutions but this needs to be a deliberate decision and you need to be aware of the impact on your image as well as the drawbacks.
Now if you want to slow the shutter speed you might try to stop down the lens to as small an aperture as you can. This will however introduce diffraction as we will cover later as well as affecting the aesthetics of the image. Rather than this approach try reducing the ISO you are using. Again, this might not have sufficient effect or you might already be shooting at the slowest ISO your camera can support. The best option however is to use a Neutral Density (ND) filter placed over the lens. These come in various strengths up to 10 stops and are incredibly useful. An alternative option might be to use a polarising filter which usually takes out 3 stops of light.
To be continued.