Tips & Techniques 2 - Hyperfocal Distance
If you focus the lens at its hyperfocal distance (HFD) you will get the greatest depth of field (DOF). Ah, now we have your attention, right?! We know you want perfectly sharp pictures of landscapes with the largest possible DOF. Hyperfocal distance (HFD) is the answer! So what is HFD exactly? First things first. Whenever you focus your lens there will be an area that is in focus (IF) and areas that are out of focus (OOF). The area that is in focus is generally referred to as the "focal plane". The important thing here is that 1/3rd of the focal plane is in front of the object you are focused on and 2/3rds of the focal plane is behind what you are focused on. Focus your lens at infinity and the leading edge of the area that is in focus is the hyperfocal point for that lens. Focus on that point instead of infinity and you will have the greatest range of focus from infinity back towards where you are standing.
The concept of hyperfocal distance is very easy to understand: focus a lens at the hyperfocal distance and everything in the photograph from some near distance to infinity will be sharp. Professional landscape photographs are often taken with the lens focused at the hyperfocal distance; near and distant objects are sharp in those photos. Basically it all comes down to this: When the lens is focused on the hyperfocal distance, the depth of field extends from half the hyperfocal distance to infinity.
When to use the hyperfocal distance (HFD)
Sometimes you don't want to use the hyperfocal distance. This is obviously the case in f.e. portrait-photography. If you want to have your model in focus and the background OOF, you do not want to use HFD obviously. Also, if you place a very strong foreground in your landscape picture, you have to make sure that the foreground subject either fits in the HFD range or you have to focus on the foreground subject and forget about HFD for this time. Why? Because depending on the focal length of the lens and the closeness of the foreground subject, hyperfocal distance may leave the focus on that foreground subject soft. Since that is the first thing the viewer's eye goes to, the whole image will appear to be slightly OOF, even if everything beyond that foreground subject is tack sharp. You basically use HFD for landscape photos, where you want everything to be sharp. From the grass, only inches away from your feet to the mountain-range hundreds of miles away.
How do you measure the HFD?
The HFD is different each time. So how do you know what the HFD is exactly? You can cheat, and many photographers do, by focusing about a third of the way into a scene. This will get you good sharp images with loads of depth of field (DOF). But if you really want to squeeze the maximum DOF out of that beautiful landscape before your lens knowing the correct hyperfocal distance for your lens (at that aperture and focal length) is the only way things can be done perfect. Like we said in the beginning of this paragraph, the HFD is different each time. It depends on a few factors. Those factors are; the circle of confusion, the aperture, the focal distance and the cropfactor of the camera. Two of those four factors are steady; the circle of confusion and the cropfactor of your camera. It is the other two factors that constantly chance the HFD and it is these two factors you should worry about. The circle of confusion is difficult to explain in non-technical terms. You shouldn't worry about it if you're just beginning to learn about depth of field and the cropfactor of your camera is easy to look up in your manual if you really want to know. If you use the following site to calculate the HFD for a certain setting or to create entire DOF-charts (more about that in the next paragraph), you don't have to worry about the circle of confusion and the cropfactor as the calculator on the site automatically chooses the right values if you enter the make and model of the camera you are using. This is the site we are referring to: www.dofmaster.com
At Dofmaster.com you can either use the 'online depth of field calculator' or the 'hyperfocal distance chart' option to create DOF-charts. Why should you make those charts? Well, out there in the field you most likely have no possibility to go online and check Dofmaster.com and your memory probably isn't good enough so you memorize all the different values. Of course you can also do some math to find out the hyperfocal distance for any focal length lens at any aperture. But since most of us do not carry around calculators in our camera bags it helps to be able to read the values of a simple piece of paper. Therefore you need to create DOF-charts. We use plastic coated cards the size of a creditcard which can even get wet.
short working with the HFD comes down to this: With every focal length combined
to an aperture there is one specific focus point that will create the largest
DOF: the hyperfocal distance. If you focus exactly on that point (in practice
that's near to impossible because how are you going to find out where f.e. 2,43
metres exactly is?) your DOF will be half of the distance of that focal point
to infinity. If the HFD f.e. is 2 metres and you focus exactly on something
2 metres away, the DOF will extend from 1 metre to infinity. Everything from
1 metre to infinity will be sharp in this example.
Like we suggested earlier in practice it is near to impossible to focus exactly on the HFD. The idea is that you know you should approximately focus on a point at 1,4 metres if the HFD is 1,4 metres and not on a point at, let's say, 3 metres. Do remember that if you don't focus exactly at the HFD, the 50% rule doesn't apply. If the HFD is 1,4 metres, only if you focus exactly at 1,4 metres the DOF will extend from 0,7 metres to infinity.
Therefore the most important thing about DOF charts is that you at least have an idea where to focus approximately. If you make DOF-charts and carry them with you, you will also know which apertures and focal lengths don't match together if you want loads of DOF. An example: if you want to photograph a certain landscape with a 30D, a 17-40 L lens and you use an aperture of f4 and a focal length of 40mm (maximum zoom with this lens) you will NEVER get a suitable DOF. Not even if you focus exactly on the HFD. The HFD at these values namely is 21,1 metres. Even if you would manage to focus exactly on that point, your DOF would extend only from 10,55 metres until infinity. That sounds okay, but isn't in reality. For starters, a DOF that starts at 10,55 metres is not very good for a landscape picture. Everything between your lens and 10,55 metres is UNsharp and of course that's unacceptable for a landscape photo. But this more important: what would happen if you would not focus at 21,1 metres but let's say at 17 metres at these values? You will then have a DOF from 7,6 metres to 70,4 metres! At the front you gained slightly in DOF (it is still unacceptable however) but in the back of your photo (after the focus point of 17 metres) your DOF will be extremely limited! Everything beyond 70,4 metres will be OOF. Unacceptable for a landscape picture. You now know these combined settings (40mm and f4) don't work for landscape photography and you can not use them together. Now you have to decide which setting you want to keep and change the other one so you will get an acceptable DOF.
Sweet spots & diffraction
Most lenses have a sweet spot. What is a sweet spot? It's an aperture, an f-value, which will get the best out of your lens. The sweet spot of many lenses is two or three stops from the maximum aperture. The sweet spot of most lenses therefore is somewhere between f8 and f11. Using lower or higher f-values than that will have a negative result on the sharpness of the image. A good guideline is to aim for the centre of your lens' aperture range. Find out what the minimum aperture is (it is likely to be f22 or f32) and then work out where the middle is. If it's f22 then the centre is f8. If it's f32 then the centre is halfway between f8 and f11. Every lens will be different, though, and if you want to be sure, you should test your lens at different apertures and see which images are most sharp. The aperture used on the sharpest image is your lens' sweet spot. Use a tripod and take shots at every possible aperture of exactly the same scene, then compare each one. Obviously there will be differences in the DOF but you should focus on a single object and compare the sharpness of that object only. A good subject would be a newspaper or something with fine detail.
Does all this mean you should avoid shooting outside your lens’ sweet spot? No, but it's good to know that if you are able to use an aperture which is close to your lens' sweet spot and still be able to get a good enough DOF, you should really do that. For the ultimate sharpness you should try to keep as close to the sweet spot as possible unless other factors like depth of field or shutter speeds dictate that you must use something else.
Diffraction is a different matter but it's also a factor which has a certain effect on the sharpness of a photo. It is a difficult and technical theory, but it comes down to this: if you use too small apertures (f22 for example) this will have a negative effect on the resolution of the image and therefore on the sharpness of the picture. Diffraction is an optical effect which can limit the total resolution of your photo, no matter how many megapixels your camera may have.
Like sweet spots diffraction is a very interesting subject and for (semi)professional photographers definately something to worry about if you want to have large prints which are still reasonably sharp. But for some people diffraction is a bridge too far we suppose. Especially because most people don't get very large prints of all their photos. We think the smallest aperture that should be used is f16, assuming you want a reasonably sharp 8x10 print. If you stop down more and still want a sharp print, you may be limited to 5x7 or 4x6 print size. For some people that's often still a big enough print.
Of course, before you reach the sharpness limit in photography, you need to fix all the other forms of unsharpness; like anything less than 100% focus, aberrations, camera shake, etc. You need to use a tripod, a remoteshutter, etc. Oh, and you need very good and expensive lenses too.