Aperture Control

[niranjan]

greetings

As i know that aperture is related to the lens and its the mechanical process to control the amount of light taken in to the camera , i wish to know how that aperture is controlled by CAMERA body ? ( in DSLR cams) i m a user of FILM SLR so its hard for me to understand the aperture control by body of the cam and not by the ring i always rotate on the LENS itself...

regds

 

[WesternGuy]

A lot depends on how you set the "modes" of your camera to capture your image. If you use the Manual mode, then it is basically the same as you are used to with your film camera - you use the focusing ring on the camera lens.

In Aperture Priority mode, you set the aperture on the camera - it will show up on the LCD panel on the camera (or whatever the manufacturer calls the display). It is my understanding that the "electronics" in the camera sets the aperture as required immediately before the image is captured. This is done through a "feedback" mechanism between the camera and a tiny motor in the lens, to ensure that focus, exposure and ISO are all "in agreement" so to speak. Information is gathered by a series of AF sensors. The data collected from AF sensors is used to control an electromechanical system that adjusts the focus of the optical system. Basically, the camera selects the shutter speed to acquire a user defined exposure in accordance with a user selected lens aperture. Now this is a very brief oversimplified explanation...you can find details here: Autofocus - Wikipedia, the free encyclopedia

If you are using Shutter priority mode, the basic principles are the same, except the computer in the camera sets the aperture based on the shutter speed that you have set, taking into consideration the ISO value as well. It all comes down to the "brains" in the camera as far as the electromechanical aspects are concerned.

These modes are referred to as semi-automatic modes, to distinguish them from Program mode, where you just use the DSLR as a point and shoot.

Hope this helps.

Cheers,

WesternGuy

 

[Helen B]

Most film SLRs control the iris operation from the body, even though you may not notice it. It's called a 'fully automatic* diaphragm' (FAD) believe it or not. You can set the required aperture using the aperture ring on the lens, and all that happens at that time is that a lens/body linkage (1) tells the body how far the aperture will be stopped down. This allows the metering system to account for the aperture. When the picture is taken another linkage (2) from the body to the lens stops the iris blades down to the required aperture immediately before the shutter opens, then it opens the iris back up after the shutter has closed. This means that you don't suffer from darkening of the viewfinder image when you stop down using the aperture ring on the lens (unless the DoF preview lever is operated of course).

This system can be taken one step further - and it doesn't matter whether it is a film camera or a digital camera. The linkage (2) can be made to close the iris down to the aperture that is set on the camera body (using either a manual setting on the body or by the metering electronics in the body), if the lens allows it. Some lenses need to be set to their smallest aperture (highest f-number) to allow the body to have full control of the iris.

These linkages can be mechanical or electronic.

*'Automatic' does not refer to auto exposure but to the automatic closing and opening of the iris when the shutter release is pressed.

Best,
Helen

 

[Edsport]

Select Av mode and select your desired aperture (check your manual if you don't know how) and the camera will choose the correct shutter speed etc. Also as mentioned you can go to complete manual mode and select your aperture but you will aslo have to select the correct shutter speed etc yourself...