Hours of Idleness-A Photographer's Journey in St. Louis

Focusing

Posted in photography, technique, Uncategorized by Jason Gray on June 27, 2010

Focusing includes all of the adjusts made that control the apparent sharpness of an image in a photograph relative to the distance between the front element of the camera lens and the subject, as well as, the distance between the back element of the camera lens and the light sensitive media inside the camera. Below is a simple rendition (from Wikipedia) of how a camera operates:

If you can imagine the small round opening as a tube with round discs of glass at either end, then sharp focus of the inverted tree upon the light sensitive media is achieved once the the front disc of glass on the tube (the front “element”) and the back disc of glass in the tube (the back “element”) reach an ideal proportion, relative to the length of the tube and other factors, between the actual tree and the light sensitive media. If you were to place a set of mirrors at parallel diagonals, in front of the light sensitive media and above it, that reflected light up and out to a viewfinder mounted on top of the camera, then you could observe the “focusing” action as you moved the box along an axis between the tree and the light sensitive media. Modern cameras, as you probably already know, have many elements between the front and back one, which help you to capture more light and produce a sharper image (among other things). The single-element lens shown above, also known as a “pin-hole” camera required a long exposure time in order for enough light to gather on the film in the back of the camera in order to produce a usable image.

There are lots of tricks to getting better focus, and here are a few of them:

1. Setting a smaller aperture (f/8 on up) increases your depth of field (the smaller the aperture, the greater the depth of field), providing an all-over focus. The down side is that you generally need more light for proper exposure, and there is usually a point in every lens where, all though everything is in focus, you start losing resolution at higher f-stops. It is worthwhile to note that the majority of lenses reach their sharpest point at about 2-3 f-stops less than wide open.

Example of a Narrow Depth of Field:

Example of a Wide Depth of Field:

2. Not a technical thing, but how you hold the camera can affect the sharpness (different than focus, but most people associate them together) of your images. The recommended camera position is holding it at eye-level, with your knees bent slightly, and with your back straight or tilted slightly back. This stance centers your gravity. Next, you should bring your elbows in as close to your chest as is comfortable, and then inhale fully and exhale halfway and pause; now you can lightly press the shutter release button (hitting it with force or otherwise jarring it suddenly can unstabilize everything just as you are taking the exposure, thus softening your image). Another technique is to lean against a wall (as straight up as possible, you don’t want to get the camera on a position off your body’s vertical axis), or to use a chair back/etc to stabilize the bottom of your camera. Vibration Reduction (VR) or Image Stabilization (IS) can give you some lee way in terms of you or the camera staying still. Of course, using a tripod or monopod will give you the best results, in terms of sharpness.

3. Your depth of field (what is in focus in the picture) extends 1/3 of the way in front of your plane of sharpest focus, and 2/3 of the way behind it. Therefore, by placing the sharpest point in your depth of field a third of the way into the scenario that you are shooting, you will achieve the maximum amount of focus possible to you at the aperture setting that you’ve chosen. Also, using lenses of different focal length (50mm, 105mm, 200mm, etc.) means that you will be working with depths of field that become naturally shorter the longer your focal length becomes, so long as your distance to the subject doesn’t change. Plus, the further you get away from the subject, using the same focal length, the greater your depth of field becomes. “As the photographer can change the aspect of the world only by changing his point of view, his distance and the focal length of his lens, he must accept the limitations, as well as the satisfactions, of his medium.” -Ansel Adams

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3 Responses

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  1. […] Focusing- controls for the apparent sharpness of the image in a […]

  2. Galina said, on June 30, 2010 at 6:27 am

    So good! Thanks for the blog!

  3. […] of field is the area of critical focus within an image.  As f-numbers increase, and the diameter of the aperture decreases, the in-focus […]


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