the network for radical unschooling families

Quantity of Light and photos

Hi Everyone,
I hope this is of interest. I don't know if this is the proper use of the RUN network, to offer photography tips - but someone will tell me if it isn't. I'm going to offer as short of a discussion on some things, and we can discuss and elaborate. You can do internet searches and find more information and read in detail.

There's 3 "ways" to affect the image that your DSLR takes, with regard to the "quantity" of light that is hitting the sensor. 1) ISO value 2) Shutter speed 3) Aperture (f/stop)

ISO VALUE: Technically what the ISO value does is change the sensitivity of the sensor. Similar to when you bought film, you bought a "slow" ISO (ASA in the old days) speed film like ISO 25 or ISO 64 for outdoor scenery. You bought "fast" film like ISO 400 for indoors or for fast action shots. The higher the ISO on a DSLR the more sensitive the sensor is. But the higher the ISO, the less robust the colors are. And you get more "noise" at higher ISO. So keep the ISO value as low as possible for the conditions. Usually you set the ISO value and ignore it for that shooting session, unless lighting changes.

SHUTTER SPEED: The faster the shutter speed, the less light reaches the sensor to create the image. A value of 1/2000 second is much faster than 1/60 second. The relationship is direct. A value of 1/500 second lets in 1/2 the amount of light as 1/250 second, and 1/4 as much as when the shutter speed is 1/125. You want a fast shutter speed to "stop" the action in sports, usually. Varying shutter speed can allow interesting images to be captured where motion is obvious.

APERTURE: This is the size of the lens hole when the image is taken. Also referred to as f/stop. Research this for explanation on the physics, if you wish. A "wide open" aperture has the largest hole, and thus lets in the most light. Values such as f/1.8 and f/2.8 are sometimes how "wide" a lens can open, and these lenses are considered "fast" lenses. As the f/stop value number goes up: f/4.0 -> f/5.6 -> f/8.0 -> f/16 and so on, the hole in the lens gets smaller, and less light enters when the photo is taken. One major point of interest is what is called Depth of Field (DOF). This is the range that is in focus (front to back) in the image. A "shallow" DOF has a short distance in focus, and this is how images have blurry foregrounds and backgrounds. You get a shallow DOF by using a "wide" f/stop, like f/1.8 or f/2.8. If you want a lot of distance in focus, then you try to use an f/stop like f/8 or f/11 (or even more 'closed down'). But remember you are letting in much less light at f/11 than you are at f/4.0, so you have to account for that.

That's a VERY brief explanation, and a bit simplistic on several points. But maybe it's a good starting point.

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