Thursday, 14 May 2015

Camera Basics - Exposure and Light Metering

Camera Basics Exposure and Light Metering.

Use your books to investigate the following in more depth.

Langfords Basic Photography
Portfolio Photography

Also use this website here

Your camera isn't going to be able to make the correct exposures in all situations. A lot of the time it will, but as you get better and start to photograph things that have interesting light, you'll see that your images will be over or under exposed. Additionally you might start to make decisions about why you may intentionally want the images to appear to be over or under exposed.

In order to ascertain whether something is over or under exposed you have to have some sense of what is generally acceptable or what it is you want to see in the image. As a rule in most instances people/clients/the viewer/your audience will want to see detail, colour, tone, form and shape as seen with the human eye. Replicating what the eye sees though with a camera, once you start to become more discerning and critical becomes slightly more complex. To get a sense of how exposure is used in a broad range of situations you just simply need to be looking at as much photography as you can. Ideally using the books we recommend of the journals and magazines in the Learning Resources Centre. The more you look at images and the more you read about photography, the more you'll learn, experiment and try the things you see and read about and be ready to learn through a process of trial and error.

The basics.

Your DSLR camera and SLR cameras as a rule with have an internal through "the lens metering system" TTL metering.

Your camera assumes the world is made up of mid - tones and in situations where this is true the TTL metering system will produce images that are 'Exposed' correctly e.g. not too dark and not too light. The camera reads the light that is being reflected off of the subject and when the subject is a mid tone if used in Auto Mode it'll come up with an exposure value (Combination of shutter speed and aperture).

We recommend that from the start you begin to familiarise yourself with your cameras Manual mode. This is set my turning the dial on top of the camera to 'M'.
Ideally you'll want to produce the best quality images and in order to do this the camera has to be set up in a way to achieve this. The basics of exposure include the setting of the cameras sensitivity to the light. This is done through the use of the ISO settings accessed either on the body of the camera or through the menu. Different cameras have different menu settings and it is your responsibility to read your manual and familiarise yourself with these basic settings.

Lower ISO values produce better quality images, so for the most part you should be aiming to shoot at 100 iso and learn how to overcome all of the problems that using 100 iso comes with. (You'll come to this later).

Setting your ISO to 100.

Generally your ISO settings will be accessed via the menu via a couple of clicks via the camera symbol and then by scrolling down and selecting 'ISO sensitivity'.

You'll then reach the fine tuning part of the ISO settings...

Turn ISO sensitivity OFF!

The main thing you now need to do is make sure your ISO settings are not on 'Auto'. Scroll right and make sure you select manual set up -choosing 100 ISO. If you don't choose to manual your camera will not be working in a way where you've taken control of the camera and the exposure and the camera will continue to make decisions for you that will restrict your learning. Remember you need to learn by trial and error and by making mistakes and learning how to correct the mistakes. If you use this approach you will gain a far better understanding of photography and light.
Figure 1.

You've now gained control of your camera and the process of using the camera with the ISO set to 100 iso will give you a far greater understanding of light levels and exposure. The more you use your camera in this manner restricting yourself to 100 iso and 400 iso as much as you can, the greater your appreciation of light levels and exposure will be.

Once set, on the back of your camera (or on top), you'll see and be able to check to see that your camera is set to 100 ISO. (No.1) in figure 1. This must not be set to Auto. Again have a look at your manual if you're unsure of how to set this or speak to your teachers.

We're insisting that you do this in order for you to grasp the difference in light levels and quickly light fades away when you move around a subject or from one space to another. This is not apparent with our eyes. When we move from one room to another, or from indoors to outside, we're rarely that aware of how different the light is. Our eyes and brains work to makes sense of the light and make the transition from one light source to another seamless. Film and digital sensors cannot do this in the same way that our eyes do, but when a DSLR camera is set on Auto ISO, I makes a damn good effort to do so and in doing so makes you lazy and unaware of how variable the light is. As light and the measurement of light is key to what we do as photographers it is essential that you appreciate the variation in light levels in your pursuit of images.

Shutter Speed.

Initially when you start to make images when you're learning we'll be advising you to always try and shoot at 1/125 of a second. This is your shutter speed. You'll be shown a demo using a Pentax K1000 where you'll see the shutter working and the affect it has when being used at different speeds.

It's the 1/125 is shutter speed that enables you to capture basic everyday movement, freezing it so that there is no blur. It's fast enough to also compensate for your own body movement so reducing 'Camera shake'.

In order to use the camera at this shutter speed you will have to be in a place where there is a lot of light. A lot of light basically means daylight outside. Anywhere else and you'll start to get problems, so when you start to shoot in this manner (ISO 100 at 1/125 shutter speed) always look to shoot your images in very bright light until you get some sense of how bright/dark different lighting conditions are.
The shutter speed is normally adjusted using the knurled wheel on the front or top of your camera body. Make the adjustments until it reaches the 1/125 shutter speed. This value is a speed at which the shutter allows the light to fall on to the cameras sensor to form the image.

Eventually we're now at the stage where you'll make an exposure calculation.

On your camera either on top of the body or on the menu display on the back of the camera you'll have feature that looks either like this..

Or like this...

You'll notice that both have a feature that looks like a dotted line with a + symbol at one end and a  - symbol at the opposite end. This is your light metering system when you're using the camera in manual mode. When your dial is set to 'Manual' the display read out will include the large 'M' on the display to confirm that you're in 'Manual Mode'.

Note. The more you keep this simple when you start the quicker you'll learn the basics.

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