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PISTILL: Zone Focusing - Hyperfocal

 
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InnleggInnlegg: 23 Ágú 2012 - 18:23:33    Efni innleggs: PISTILL: Zone Focusing - Hyperfocal Svara með tilvísun

Þetta var í digital-photography-school.com í dag. Mjög fróðlegur pistill ef maður nennir að lesa allt. Þetta fjallar eiginlega um hyperfocal focusing.
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http://digital-photography-school.com/ultimate-guide-to-zone-focusing-for-candid-street-photography/comment-page-1#comment-312130

The Ultimate Guide to Zone Focusing for Candid Street Photography

(sleppa inngangsorðum)

DEPTH OF FIELD (dof)

Before we go into what zone focusing is, we need to talk about the factors that go into creating DOF. If you know this already then feel free to skip to the next section.

The term Depth of Field refers to the area in front of and behind a subject that you focus on that will appear acceptably sharp. For instance, say you focus on a subject that is 10 feet away. Depending on your camera settings, that might mean that everything from 8 feet away to 14 feet away will be acceptably sharp. That would be your depth of field. Also, keep in mind that the area behind your subject that is acceptably sharp will always be greater than the area in front of your subject, and in many cases much greater.

Depending on four factors, your aperture, your focal length, the distance that you are focusing at, and on your camera’s sensor size, your depth of field can change drastically. Here are the four factors in detail:
The smaller your aperture, the more DOF there will be in a scene. So if you are shooting at F16, much more of your scene will be sharp than if you are shooting a F2.8.
The wider your focal length, the more DOF there will be in a scene. So if you are shooting at 28mm, much more of your scene will be in focus than if you are shooting at 100mm. This is why I rarely zone focus using a lens longer than 35mm.
The further away you focus, the more DOF there will be in a scene. So if you focus on a person 10 feet away, then you may have a range of three feet in front and six feet behind your subject that will be sharp (depending on the other three factors), whereas if you focus on a person that is 3 feet away, you may have a range of 3 inches in front and 6 inches behind your subject that will be sharp.
The larger your camera’s sensor is, the less DOF there will be in a scene. If you are using a full frame camera like the Canon 5D, then there will be less DOF then if you are shooting with a camera with a smaller sensor, such as the 7D, 60D, or a micro-4/3rds camera, with the same settings.

Here is a website to test out these different depth of field factors: http://www.dofmaster.com/dofjs.html. Keep in mind that the term ‘acceptable range of sharpness’ is just an opinion. As your subjects veer further from the focus distance of your lens, they will appear less and less sharp, whether or not they are in the ‘acceptable’ range on the chart. So practice with your own camera and lens to figure out what is ‘acceptable’ to you. This website is only a general guide to get your started.

ZONE FOCUSING

Zone focusing is pre-focusing your camera to a certain distance away, say 10 feet, guessing the DOF that you will have at that distance with the settings you are using, and then photographing subjects as they enter that range, and hopefully as close as possible to the actual focus distance on the camera.

It is also being able to change your focus distance quickly and accurately, without looking, as a subject moves closer or further from you.

The reason for doing this is that both using autofocus and turning the manual focusing dial takes time (and often will be noticeable to your potentially candid subjects) and most of the time things happen so fast on the street that you need to be focused ahead of time. If your camera is already focused to an average distance away, then you can just wait for your subject to enter that range and there will be no delay from when a moment happens to when you are able to click the shutter. It will be instant. In addition, this will allow you to shoot without looking through the viewfinder, if you decide that you want to ‘shoot from the hip.’

Here is a specific example based on common settings that I use. With the 5D Mark II and a 28mm focal length, if I pre-focus my camera to 8 feet away at F8, then everything from around 5.5 feet to 15 feet away will be ‘acceptably’ sharp. Of course, as you get to the outer areas of that range the subject will not be perfectly sharp, but for fast-moving street photography, it gives me a serious range to work with. At F11 or F16, even more so.

The only problem is that you need to have a lens with a manual focusing meter, such as the one in the photo above, that shows you the distance that the camera is focused at and is easily manipulated. Many cameras and lenses don’t have this but some will tell you the focal length in the camera’s menu or viewfinder. While not perfect, this will work somewhat.

But if you want to do candid street photography then I highly suggest getting a lens with a manual focus meter.

So it should be obvious to you why we generally want the range of sharpness to be as great as possible when zone focusing (unless you want more bokeh for aesthetic reasons). It is for when we mess up slightly in guessing how far something is away so that there will still be enough leeway for our main subject to be sharp, or so we can get multiple subjects at different distances to all be relatively sharp. These are two reasons that many street photographers prefer to use wide-angle lenses, such as 28mm or 35mm. My go-to focal length is generally 28mm.

It is also the reason why you want to shoot at a high ISO in street photography (unless the light is strong). If you shoot with a high-ISO, it allows you to shoot with a smaller aperture. With my 5D Mark II, ISOs of 800, 1600, and 3,200 are usually my standards (unless the light is strong). For many cameras, the ISOs may not be ideal at these levels, however that is quickly changing these days with each new camera released. Test your camera at different ISO settings to see what its acceptable range is.

GUESSING DISTANCES

If you are like me then you often do street photography in less than ideal lighting, such as in the subway system. When you’re shooting at F16 in bright sunlight, you don’t have to think as much about it. It won’t matter much if your subject is 9 feet away versus 10 feet away. But when you are shooting at F2.8 in the subway, it really does matter.

For this reason, it is important to learn the distances away from your camera’s lens, all the way up to around 12 feet away. I suggest using a tape measure and measuring out the distances, from 2 feet from your lens all the way to 12 feet.

Go out and practice. Find different objects and try to guess how far they are away. Before I go out I will still pick an object around eight feet away and focus on it to make sure I’m guessing my distances right. It’s a skill that you need to constantly calibrate. I have gotten a lot of strange looks over the years from people who have seen me focusing intently on lampposts 8 – 10 feet away.

The other reason to get good at guessing distances is that people move and scenes develop. You might want to capture a person walking towards you at both 10 feet and 5 feet away. So when you hold the camera you want to always have one of your hands on the focusing ring. Practice manual focusing back and forth from 10 feet to 8 feet to 6 feet and so on. Eventually, you’ll be able to capture someone walking towards you sharp at both 10 feet away and 6 feet away, without having to look through the viewfinder. It’s an incredibly effective technique. Doing this well, however, can be tough.

My final word of advice is that if you have the time to autofocus or manual focus with a viewfinder on a subject without them noticing, then do it. That is much more consistently accurate than trying to guess distances and zone focusing. But for a majority of the time, zone focusing will be your best and quickest weapon on the street.
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Skráður þann: 17 Ágú 2005
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InnleggInnlegg: 23 Ágú 2012 - 19:04:35    Efni innleggs: Svara með tilvísun

Það er alltaf gaman að birta þetta.



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