What is SLR & D-SLR Camera?

SLR



A single-lens reflex (SLR) camera is a camera that typically uses a semi-automatic moving mirror system that permits the photographer to see exactly what will be captured by the film or digital imaging system (after a very small delay.

D-SLR



Most digital single-lens reflex cameras (digital SLR or DSLR) are digital cameras that use a mechanical mirror system and pentaprism to direct light from the lens to an optical viewfinder on the back of the camera.

The basic operation of a DSLR is as follows: for viewing purposes, the mirror reflects the light coming through the attached lens upwards at a 90 degree angle. It is then reflected three times by the roof pentaprism, rectifying it for the photographer's eye.


How to use aperture priority, AV (for Canon) or A (for Nikon) mode on your digital SLR camera
For photographers who use SLR cameras, AV or A mode determines whether all the photograph is in focus or part of. For example photographers can choose to have a sharp foreground and background, or they can blur the background.

On SLR digital cameras, aperture is indicated by a f-number value.


The higher the F number, the more of the photo that will be in focus. For instance if you're taking a photograph of a landscape, chances are you will want all of the foreground and background to be sharp and in focus. For this to happen you will need to set your digital camera f value or aperture as its known, to a large number, for example F/11.

On the other hand if you're taking a photograph of a bird and you want the animal in focus but not the background, then you would choose a small F number like F/4.

You can see what aperture your digital camera is set at by looking at the back LCD screen for a F number. As you can see by the image above right, the aperture in that example is set at F4.0. The display shown on your LCD may look different to this example, depending on the make and model of your camera.


How to set your camera to aperture priority?
The letters AV (for Canon camera's) or A (for Nikon camera's) on your mode dial sets your digital SLR camera to aperture priority. Your camera then changes all other settings such as shutter speed automatically to suit.

Once you have AV mode turned on, you can change the f-number by rotating the main dial above the shutter button. Note: this is for Canon digital cameras. You may need to refer to your manual to find out how to change the F stop for your specific brand of camera.

When the f number is small, the lens diaphragm is actually wide open. So if someone says to you that you need to open your lens more, they mean to lower the aperture or F number. Alternatively, if the aperture is a large number, say F22 then the lens diaphragm is smaller or more closed. This often causes much confusion with beginners.
Opening your lens more refers to lowering the f number.
Closing your lens more refers to a higher f number.
The best way to understand how aperture works is to take numerous photographs with different f-number values and see what the difference is.

Take images at both ends of the scale. One with as low a F number as possible and one with as high a F number as possible. More importantly, when you view them on your computer take notice of how much of the photo is in focus.

Blurred Example



Source:http://www.slrphotographyguide.com/camera/settings/av-mode.shtml