Combined Shutter and Aperture Priority Mode TAv

Automatic Metering Mode with Control of Aperture and Shutter Speed

May 17, 2009

This is an automatic digital camera mode enabling photographers to control portrayal of motion and depth of field. ISO becomes an exposure control for the digital age.

This priority mode is available on the current Pentax K20D, and older K10D, top of the range DSLRS and is one of the dial mode options. The two adjusting thumbwheels near the shutter button adjust the aperture and shutter speed. The camera’s metering system sets the light sensitivity, or ISO, optimizing the image’s exposure.

In the viewfinder the Pentax cameras display the current Aperture, Shutter Speed and working ISO level enabling photographers to juggle a combination of all three exposure factors to achieve their creative objectives.

In some situations being able to switch between straight Aperture Priority, or Av, mode with a fixed ISO to one with auto ISO and control over shutter speed, all with the turn of one dial is more convenient and efficient than menu functions or combinations of switches.

Alternative Systems

The more common auto ISO function approximate the result of the TAv mode but usually only allows photographers to control one other exposure variable. To achieved the same functionality in other cameras there may be two controls need to for the mode and ISO settings Busy photographers find it easier to operate one dial to switch to TAv, making it clear the camera is in Auto ISO mode

Shutter speed Priority

There are two important factors governing the photographer’s choice of shutter speed. Firstly, when capturing moving subjects the shutter speed determines the amount of blur if any. This is covered in an earlier article Camera Shutter Speed

Aperture Priority

The effect of aperture size on the appearance of the image is not confined to the exposure levels, it is also important in determining the depth of field in the image. This is covered in more detail in this earlier article, Photography: Aperture

Sports Shooters

Sport and action photographers like to isolate the subject using a shallow depth of field to blur the back and foregrounds of an image. This comes with the long focal length lenses and wide apertures used, especially in dim conditions where high shutter speeds are preferred to control the portrayal of motion.

Landscape Photographers

Despite first impressions, landscape photographers often have limited time to take their photographs as changing light and weather conditions are beyond the photographer’s control. There may only be one chance for that perfect combination that may preclude the use of a tripod so as well as the normal important control of depth of field via aperture, shutter speed to minimize camera shake while hand holding may be more important than a noise penalty from higher ISO. The grainy effect produced by high ISO may enhance the atmosphere of the image. Hand holding for serious landscape work is more likely with the in-body image stabilization in later the Pentax DSLRS working with the classic Pentax prime lenses.

The copyright of the article Combined Shutter and Aperture Priority Mode TAv in Photography Techniques is owned by Philip Northeast. Permission to republish Combined Shutter and Aperture Priority Mode TAv in print or online must be granted by the author in writing.