Some Tittle Reading from Forum (Just to Share)

I have read this article in one of the Photo Forum. So, just want to share it here.

1. What is exposure?
Exposure is measured, either manually or automatically, before you press the trigger on the camera to take a photo. You will need the right exposure for your photo to appear right.

When we take a photo, in order for the medium of capture, be it film or digital, to produce a similar scene as we see, we need to ensure that we give the right information to the camera. The information given is called exposure. If you give too much exposure (overexpose), your photo will come out blown; too little (underexpose), and it will turn out dark. Both of which will also result in loss of details in the photo. With most basic point and shoot cameras, the measurement and adjustment for the proper exposure is done for you automatically. However, with higher end cameras, like the SLR, you would have control over the exposure; hence allowing you more freedom of creativity. Exposure is determined by a simple equation, i.e. Exposure= amount of light x duration. The former is controlled by the aperture; while the latter by the shutter speed.

2. What is aperture?
Aperture controls the amount of light that enters the camera to reach the medium of capture. It is measured in terms of f-stop values.

Any opening that is placed in front of the medium of capture to control the amount of light reaching the medium is an aperture. The difference is whether it can be controlled or not. A fixed aperture point and shoot camera and a pinhole camera is two examples where the opening is fixed at a certain diameter. In such cases, the aperture value cannot be adjusted. SLR and certain high end point and shoot allow you to manually control the aperture values. The opening of the aperture and the amount of light allowed in with regards to the size of the medium is measured and denoted in f-stops. The f-stops is necessary to ensure standardisation among different mediums, i.e. A f/8 aperture on a 300mm lens and a 50mm lens will both let in the same amount of light on the medium of capture despite the difference in size and length. A larger f-stop value denotes a smaller opening, thus letting in less light; and vice versa. F-stops is measured in a linear fashion. Every time you double the f-stop value, you get +2 stops exposure. Some of the common f-stops value includes f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22 and f/32. The difference between f/2 and f/4 is two stops exposure, while f/2 and f/2.8 is one stop. Aperture opening also determines the depth of field of the photo.

3. What is shutter speed?
Shutter speed controls the amount of time the aperture opening is left opened for light to enter. It is measured in fractions, which doubles or halves the duration.

To control exposure, we not only need to control the amount of light that enters the medium of capture, but we also need to control the duration that amount is let in. This is where shutter speeds come in. Shutter speed is essentially the control that allows you to control the duration the aperture is opened. It is measured in fractions of seconds. The common shutter speeds available includes 30s, 15s, 8s, 4s, 2s, 1s, 1/2s, 1/4s, 1/8s, 1/15s, 1/30s, 1/60s, 1/125s, 1/250s, 1/500s, 1/1000s. As you can see, the values are either double or halve the amount of the previous speed. Each different speed gives you one stop difference in exposure.

4. What is ISO?
ISO is the sensitivity of the medium of captured to light.

ISO was originally designed for film, by compensating on the grain size, the films created need less light to achieve proper exposure but at the cost of blurred margins and large film grains. Digital took the same principle onto their sensors, but the end compensation is noise instead of film grains. Essentially, ISO value is how sensitive a medium of capture is to light. The lower the ISO, the finer the details are rendered in the end product. Common ISO values are 50, 100, 200, 400, 800, 1600, 3200 and 6400, with the last one more common for digital medium. Each ISO values are either double or halve of the previous value, just like shutter speeds; and with that, each difference of value also give you a one stop difference in exposure.

5. What is exposure value?
Exposure value or EV is the value given for an exposure. While knowing the exact value for a given exposure has little usage for your everyday photographer. It is useful to know that it exists. Each difference of value is one stop. So if you adjust your digital camera to +1EV, you are allowing more light into the camera and vice versa for -1EV. Each stop doubles the exposure of the medium of capture to the light, either by allowing more light in via aperture adjustments or allowing a longer duration for the light to enter via shutter speed adjustments.

6. What is push/pull?
Push/pull is only valid in films. The ISO for any given film is only a recommended value. You can shoot an ISO100 film at ISO400 if you are familiar. The technique of changing the ISO is call pushing or pulling. Pushing is when you rate the film at a higher ISO and pulling is for a lower ISO. Push/pull is important because you need to tell your developer about it if you decide to do pushing/pulling, so that he/she can do the necessary adjustments while developing.

7. How do you measure the right exposure?
Exposure can be measured using a light meter. There are many types of light meters in the market, most them in-build into the camera. While the usage of these meters is up to your initiative to read the manual that comes with the equipment, it is good to know what types of light meters there are out there and how they function.

There are two types of light meters, an incident light meter and a reflective light meter. The incident light meter measures the light that is falling upon a surface; while the reflective light meter measures the light that is reflected off a surface. The latter would be more useful in photography as we are often capturing the light that is reflected and different surfaces might reflex different amount of light. Most modern cameras have multiple segment reflective light meters built into them. These cameras measure the reflected light at various points in the scene and average it out to give you the ideal exposure. However, as all things automatic, it is not foolproof. It is still better if you know how the meter in your camera works and be able to compensate for proper exposure in certain situations.

8. What is sunny-16 rule?
If you are stuck in a situation without a light meter, the sunny 16 rule is a rough guide for you to estimate the exposure of the scene. The rule is such: On a bright sunny scene, the exposure is 1/ISO used at f16. So, if your ISO is rated at 400, the correct exposure in a sunny scene is 1/500s at f16. Increase your exposure by one stop if it is slightly cloudy and two stops if it is heavily overcast.

9. What is 18% grey/ middle grey?
18% grey is a card issued by Kodak. The light reflected of it is said to give you the idea exposure for a scene. So if you place an 18% grey card in the middle of your scene, measure the reflected light off the card, and shoot the scene at that exposure; your photo would turn out as seen. In other words, an ideal exposure is the exposure value measured off an 18% grey card.

10. What is zone system?
A system created by Ansel Adams to make beautiful pictures.

The zone system was created by Ansel Adams back in the black and white days. It was originally created to be used to maximise the potential of black and white films and prints. However, it can still be used in today’s modern photography. To write about the zone system in detail required a whole book. I would suggest reading “the negative” by Ansel Adams if you want to know more about it. To describe the zone system briefly, the system is actually a series of 11 exposures, ranging from zone 0 to zone IX. In the middle, zone V is the exposure measured at 18% grey, and zone 0 gives pure black; zone IX pure white. Everything else falls within the other ranges. The idea of zone system is to visualise the end-photo before shooting it, and by using the zones as a guide, you can determine which part of the photo you want to be properly exposed and others really dark/bright. It’s a very useful technique that can help a photographer evaluate a scene in a methodological manner.

source from : www.photomalaysia.com