The distance from the closest to the most distant part of a motif that is sharp is called Depth of field (DOF). DOF affects all pictures – sometimes you want DOF to be shallow to bring out and concentrate the interest on your sharply focused main motif while the background is blurred … other times you want sharpness from close up and all the way to infinity – with a really deep DOF! This post is both a general post on DOF but it also contains specific samples that relates to the Canon PowerShot S95!
All cameras with a small sensor – and a correspondingly short focal length on the zoom lens – has a depth of field (DOF) that is quite deep! This applies also to the Canon S95 with its 6-22.5 mm zoom lens. For a DSLR with a bigger sensor it is a little more varied – but usually the DOF is more shallow. This can be both good and bad – depending on how you want your picture to turn out!
(The picture above is taken with Canon EOS 550D 18 mm and f 11.0 – to get a deep DOF. Not shown full size.)
The DOF is affected by three things:
- Focal length
The shorter focal length (you might like to think of it as wider angle) the deeper DOF and (it follows) the longer focal length the narrower DOF.
The smaller the aperture (that is bigger f-value) the deeper DOF and larger the aperture the narrower DOF. You really need a large aperture to get a nice blur!
One complication with most zoom lenses is that they vary the aperture as you vary the focal length!
- Distance to the motif
The more distant you are to the motif the deeper DOF and the closer you are the narrower DOF
All of the above factors are combined so that:
The deepest DOF you will get when you are using a very short focal length, a small aperture and are very distant to your motif!
The most shallow DOF you will get when you are using a very long focal length, a large aperture and are very close to your motif!
Depth of Field diagrams
To keep things reasonably simple I will look only at the extreme values: widest angle and most tele – with biggest and smallest aperture. Moreover I have limited it to two focus points at 1 and 6 meters.These 8 cases I have plotted in a DOF Diagram for the Canon S95 – and as a comparison I have included a DOF Diagram for the Canon EOS 550D 18-55 mm . The two top rows are showing the tele results and the three bottom rows showing wide angle. The small black marker on top of each bar is the focus point (1 or 6 m) and you can see how the DOF spreads out around it (the green/violet bars). Note that as you goes towards smaller apertures the DOF behind the focus point increases a lot!
Canon S95 DOF diagram. Looking only at the two most extreme combinations – for deepest and most shallow DOF:
Using wide-angle, f8.0 and focusing at a close object at 1 meter we get a DOF of 0.43 m – infinity. That is close to the deepest DOF you can get with the S95! Handy for landscape pictures or whenever you want everything to be sharp! Notice also that it does not matter that much if you focus on something 6 m away instead – you will still get almost as deep DOF of 0.7 m – infinity!
If you use the largest aperture (f2.0) you will still get a relatively deep DOF at a distance but it will get more shallow at 1 m.
Using the largest aperture with tele, f4.9 and focusing at a close object at 1 meter we get a DOF of only 0.95 – 1.06 m. That is a reasonably shallow DOF! Handy for a portrait (face only) or where you want only the main motif to be sharp! Here it does matter a lot if you focus 6 m away instead – you will get a DOF of 4.5 m – 9 m! At around 6 m this works well for a full picture of a person and a few meters more will handle a whole group of people – who does not have to stand on a line either! You will get a blurred background – but (I am sorry to say) only slightly blurred.
If you use the smallest aperture (f8.0) you will still get almost as shallow DOF at 1 m but at 6 m distance the DOF will increase a few meters! Note that the only way to accomplish a really blurry background is when you take pictures really close up … Also note that due to the fact that the aperture in the tele setting is f4.9 you will not get an extremely blurry background if your motif is a few meters distant!
Looking only at the two most extreme combinations – for deepest and most shallow DOF:
Using wide-angle, f22 and focusing at a close object at 1 meter we get a DOF of 0.43 m – infinity. (Same DOF as the S95 but with a very different aperture!) Again that is close to the deepest DOF you can get with the wide-angle!
If you use the largest aperture (f3.5) you will still get a relatively deep DOF at a distance but it will get more shallow at 1 m.
Using the largest aperture with tele, f5.6 and focusing at a close object at 1 meter we get a DOF of only 0.97 – 1.03 m. That is a very shallow DOF! To be used where you want only the (small) main motif to be sharp! If you focus 6 m away instead – you will get a DOF of 5 m – 8 m!
Here it is a little easier to accomplish a really blurry background when you take pictures really close up … But note that 55 mm is not long enough to give a really blurry background at a distance! You will need 100-200 mm lens to accomplish this on a half-size sensor camera like the Canon EOS 550/Canon Digital Rebel T2i!
I have already said this (in the 3 points above) but want to stress that – for all lenses – as you move away from your motif the DOF increases (can be seen very clearly in the diagrams) giving you less and less blurry background. If you focus at 18 m you will with the S95 at the longest focal length and largest aperture (f4.9) have a DOF stretching from 9 m to infinity – not much hope for a blurry background there – but on the other hand you will get a picture where most of it is in focus – could also be handy sometimes…
Want to dive deeper into the shallow depth of DOF? 😉 Then go to Wikipedia for a much longer and much more detailed take on the subject with formulas, diagrams etc…
Blurry background – Portrait or flower
You probably want a nice blurred background to make your motif stand out. Ask your motif to move away from the background (flowers – I am sorry to say – only moves when you want them to be still! 😉 ) – the further away from trees, houses etc the better! Then use your zoom at its maximum tele setting (if you have one of those super-zooms you don’t need to overdo it 🙂 ) and you step back from your motif – but only as far as is absolutely needed to get enough coverage of your motif! Make shure that the camera (or you) select as large aperture as possible!
(The picture on the left is taken with Canon EOS 550D 55 mm and f 5.6 (full open) – to get a shallow DOF. Cropped and shown half scale.)
If you want blurry background when photographing a flower: On many compacts you can only use the “macro” setting with the wide-angle! Accept it (you might like it) – or try to go as close as possible with maximum tele setting – this is by far the best way to get a nice blurry background!
The whole picture turns out blurry? Then you have shaken the camera – hold it more still – get some support! Tree, rock, table or … maybe even a tripod! You can also get a totaly blurry picture if you have missed the focus completely!
Blurry background – Group of people
Assuming you want the whole group to be sharp – first of all you have to have them all at roughly the same distance! For blurry background you do the same as with the portrait or flower above: Position your group far away (at least 10-20 m) from the background! Use your largest aperture and as much tele as you can and then you walk away – but only as far away from your group as needed – until you get them all to fit in the picture (with the tele setting). The only special handling with a group is if they are not standing at exactly the same distance: focus on one of the nearest persons in the group. Assuming that the nearest and most distant person are not more than a meter or two apart you will get a sharp picture of the whole group and a somewhat blurry background. The longer tele lens you have the nearer on a “line” the group must stand – but the “blurrier” background you will have!
Sharp background – Person or group in front of Eiffel Tower
Or any other picture where you want the surroundings to be seen clearly. Here you probably want a deep DOF so that as much as possible can be seen clearly. First of all you move away from your foreground motif and use your wide-angle. To get maximum DOF you should also use the smallest possible aperture. But also take one picture with what f-value the camera suggests – it might be good enough.
Canon S95 DOF Samples
First of all I must disappoint all of you who is hoping to get a very blurry background in your portraits with the S95 – or any other small sensor short focal length lens cameras! It will not happen – even with a large aperture lens as the f 2.0 one on the S95! But as largest aperture at tele is just f4.9 you will only get a really blurry background when you use max tele in a very close up picture – that will not cover a view big enough for a proper portrait – but might work for a close-up of a flower for example. If you have a super-zoom you are luckier but will need to use the tele setting and hold the camera very very steady!
I have taken two series of pictures samples. You will see a variation of the DOF but it is so small it hardly is worth mentioning.
The first series in which I vary the focal length from 28 mm to 105 mm (equiv – in reality 6-22.5 mm ) and use the lowest possible f-value. This affects the perspective – more than it affects the DOF. The difficulty here is that the Canon lens is only f2.0 at the wide-angle end – and f4.9 at the tele end. So as I zoom to tele I also increase the f-value and thereby keep the DOF almost constant.
The second series I kept the focal length at a mid position and varied the f-value. Also very little variation of DOF!
As the DOF variation is so small I have just put up the extreme samples – but trust me – the intermediate pictures looks much the same! All pictures are taken with AWB – which handles the flourescent energy-saving lamps quite well! The hat sits 50 cm in front of the wall.
Looking at the above pictures you can easily see that for the Canon S95 the first picture has the most blurry background. This is due to two factors: I am closer to the motif and can use f 2.0 – this together affects the background most thus giving the most shallow DOF – even if I use the wide-angle! And a hat – contrary to a person – usually does not complain about certain features (like the brim) looking a bit wide! 😉
I will add a few extra samples with the motif further away from the background to illustrate how blurry you can get the background – as soon as the weather improves! (We have had the coldest winter for at least 150 years!)
If you want to have really seriously blurry background with an ordinary zoom compact – you have to fire up your favorite image software and get to work! Or get a super-zoom… If you on the other hand want to have a deeper DOF than you can get with your camera and lens combination – then you can combine several pictures with different focus into one picture with a lot of work in Photoshop or similar – or you cold just use CombineZP that automates the process.
Hope this throws some light on DOF for us photo amateurs!