Digital Photography - Aperture Priority

Aperture Priority controls the amount of light streaming through the lens and striking the photo sensitive element. Depending on the Focal Length of the lens Aperture settings will set the Depth of Field (DOF) for the object in the image.

Another important figure is the Hyper Focal Range (HFR) created by the Aperture opening. As the Aperture opening is closed to smaller diameters the Aperture figure increases and the DOF and HFR values increase.

Each lens will have a range of Aperture values, the first is the widest value, and the second is the smallest value for that lens. Some after market lens manufactures will include a scale calibrated in Ft. and Mm to indicate the DOF and HFR range at popular Aperture Stops.

When you increase the Aperture setting from F-4.5 to F-22 the HFR increases as well, and may need resetting for the ISO or Shutter Speed for a proper exposure.

The Point of Focus becomes the central focal point, and the Depth of Field extends beyond the central point and closer to the camera lens.

The Hyper Focal Range is the total focus within the DOF figures and can be adjusted with the manual focus ring on the front of the lens.

You can shift the HFR to bring slightly out of focus objects into sharp focus, or allow them to fade into soft focus.

Another example that becomes very important when making portrait pictures:

You set the central point of focus on the subjects eye, the most critical area to be in "Pin Sharp" focus.
The Aperture setting is at F-5.6 with the ISO at 200.
Using the "Preview" button on the lens, or camera body you notice the eyes, ears, and back hairline are in sharp focus, but the tip of the nose is in soft focus.
The HFR is calculated to be 8 inches.
The DOF is 4 inches behind the eyes, and 1.5 inches in front of the eyes.
Pressing the Preview button you can adjust the lens focus ring slightly to bring the tip of the nose into sharp focus. (Please note you may have to turn off Auto Focus on the lens.)

Adjusting the HFR can be used on all types of subjects to create an interesting pictorial effect. A mountain scene with a lake, mountains in the background, and a small island in the foreground. You can shift the HFR to bring all subjects into sharp focus, allow the mountains to become soft focused and the island in sharp focus, or let the island fall into soft focus and have the mountains in pin sharp focus.

The HFR adjustments will have dramatic effect on all types of lens groups. Wide Angle lenses will have the greatest effect with HFR, telephoto lens will have a lessor effect but will enable sharp focus on the main subject, and Macro lens will require adjusting the HFR to obtain sharp focus.