My Photo Blog

Depth Of Field Part 1

In a previous blog I discussed focus and just touched on depth of field. To make things clear from the start, focus is a flat plane that lines up parallel with your lens and film plane. It is a point that everything in front of it, or behind it is technically out of focus. Depth of field is an illusion created by your aperture, magnification, the physical size of your film, or sensor, and the point of focus. The image beyond the exact point of focus is referred to as circles of confusion, and as long as the circles are small enough, there is the illusion of being in focus. Wide angle lenses are the best at creating that illusion, because of their low magnification when shooting a landscape, or other distant subject matter. Normal, telephoto, and macro lenses are used when you want to get closer to your subject, which increases magnification and reduces the depth of field. The one control a lens has to compensate, is it’s aperture. The larger the f/stop number, the smaller the aperture becomes and the greater the depth of field. An example would be a lens set at f/32 would give you a greater depth of field compared to the lens set at f/2. Where you chose to focus in the scene also effects depth of field. A rule of thumb is to pick a focus point of about 1/3 into the scene to achieve a look of overall focus. With todays digital cameras, zooming in on live view and focusing through a loupe also works well. One note about stopping down is that most lenses preform best at mid range f/stops and lose quality as the aperture reduces beyond that point. In a future blog post, we will look at lenses and cameras that utilize tilts and swings to extend the visual depth of field.



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