Focus-Exposure Lock

Before I start off, let me tell you that this is one of the things that I find very irritating when a friends says that he/she doesn't know what it is and how to use it. Come on, if you call yourself a photographer or are even trying to be a decent photographer, then you ought to know how to use this feature of the camera.

What it is
So... focus-lock is also referred to as half-press, exposure-lock and so on. In most of the cases, unless your camera has a dedicated button for focus-lock or exposure-lock, this button is the shutter press button. Or, in other words, the same button that you click to take your photographs. Let us call this button the shutter-release from now on so that we have a consistent naming convention across this post.

The feel of this button
Now this is what it is. Unless you have a really cheap or feature-less camera then your shutter-release will have two steps of clicks as you press it. Most importantly you have to realize the feel of this button before knowing what it does. Unless you are able to press it correctly, there is no point knowing what is its use. So pick up your camera and bring it to the computer. There is no need of switching it on as this is a mechanical button and will work the same whether your camera is on or off. If your camera is really old and you have been monstering your way through that button, then it might have become soft and you wont realize the feel, and it might well be harder for you. I have seen this happen in only one camera till now - a friends Sony DSC-H1, where after less than a years use the button lost its half-press sensitivity and the functionality was totally lost.

So, now that you have your camera with you, take position and press the shutter. Give a slow/soft/slight pressure with your finger(I do hope you use your index finger to click. You can use other fingers of course, but the index finger is most responsive to touch/pressure and you are most likely to find the half-press point with this finger) and push the shutter down. Some cameras might have a hard shutter and this might need a harder push with your finger. Nevertheless, keep a constant pressure on the shutter and maintain that pressure as you push the shutter down. Feel the shutter as you push it down. At one point the shutter will stop and you will feel as if it has been pressed down fully. Of course, if it is your first time then you might well have pushed it all the way down. ;)

Keep trying this till you get that mild jerk/feedback as you slowly(really sl-o-o-o-w) push the shutter-release down. You will know that you have reached the half-press point if you get the feedback but you can still press the button all the way down. That is exactly what this half-press button is. If you press it half-way(till the click or feedback point) it does some functionality without taking the photo and if you push it all the way down, then it actually takes the photo. Try this again and again till you are able to get the half-press point every time. Increase the speed of the shutter-release, by giving more pressure each time, till you get really comfortable with this process.

Seeing it in action
OK, its great that you were able to find the 'sweet spot' on the shutter-release. Now the interesting part. You actually have to hold it at that point for about half a second to one second. Again this duration is dependent on the camera. If you press it completely by mistake or release it a little bit then the effect, and effort, is lost. Let us now see this feature working so that you know whether you are holding it at the spot correctly or are releasing it prematurely.

So switch on your digital cameras and keep it in the shooting mode, ready to take pictures. You will see a small square in the center of your LCD screen. This is how it is in most of the point-and-shoot cameras. In case of other more advanced cameras, when you look through your viewfinder(Optical or EVF depending on whether you are using an SLR or an ultra zoom camera) or the LCD screen, you will see a square, multiple squares, a dot, or small squares/rectangles with dots or cross-hairs in them. Whatever it is, these are the focusing points on your camera.

Now when you half-press the shutter-release button, while attempting to shoot an image, you will notice one or many of the following things.
1) The focusing point(square or cross-hair, or dot) changes color or flickers with a different color. i.e in some cases the square turns red, in some cases the dot within the square turns red and so on. You will notice a marked change in the focus indicator.
2) There is a green/red circular spot that appears on the screen. Mostly in the top area.
3) The screen flickers and shows an exposure change. An exposure change means the image on the screen becomes brighter or darker or just flickers.
4) The image blurs and then becomes sharp again. This indicates that the camera is focusing.

This is the half-press point. To confirm that you are pressing it correctly, you can check that the indications mentioned above happen just once. Once the indication happens, it continues to remain that way on the screen, i.e screen doesn't keep flickering, the green spot stays continuously on the screen and so on.

If you release the shutter-release button then the indication disappears or if you press it completely by mistake then the photo gets taken. Try holding it at this point for a few seconds so that you are comfortable with the amount of pressure to keep on the button. Once you are comfortable holding it at this point for long time, depress it completely. You will find that the image is taken. Try to take the image as you would do normally - completely pressing the button at once and notice the behaviour of the camera. Then try to hold at half-press point for 2 seconds and then take the image and notice the behaviour of the camera. Try and compare these two ways to take a photo and note down the differences and try to find out what is happening.

In the next post we will take a detailed look at what functionality this offers and how it will improve your photo taking skills.

Metering

I am continuing my blogs on photography after a very long break and this time I will talk about another one of the important terms that define a photograph. The term is called metering.

Metering is the way the camera judges the brightness or darkness of the image. When the camera sensor looks at an image, it had to judge how bright the image has to be before attempting to capture it. Another term for this is exposure, as we had seen previously. If you have an image or a scene that is mainly white but has a small dark coloured object of interest in the center, then it is very likely that you will miss the object or you will not see the finer details of that dark object. In the case of a camera, the camera has metered the images for the bright areas and hence loses the details of the dark object. Similarly, if you have a predominantly dark image, such as in a dark room, and a small bright object, such as a bulb, then the camera will meter for the dark areas and the bright object will look washed out or over exposed.

You can understand this by relating to your own experiences in photography. Have you ever tried to take a photograph of the moon on a dark night with a simple point-and-shoot camera without a huge zoom? You would have probably noticed that the moon would appear totally white against the black background and you would have lost all the details on the moon, such as the craters. This is because the image is predominantly dark and the camera processor has been trying to take the photo as brightly as possible and in the process made the bright object even brighter and has hence overexposed it.

You can also imagine how the brain does this metering. Suppose you enter a dark tunnel in a fast moving vehicle. A fast moving vehicle because you don't want to give your brain enough time to adjust gradually, like when you are walking into the tunnel. So, when you enter the tunnel, everything goes dark and you are not able to see anything. This also happens when you walk into a room at night and switch off all light. For an instant you cannot see anything and all goes pitch dark. Slowly, your eyes adjust to the situation as the brain begins to meter the scene for darkness and you are able to see/identify the presence of objects in the dark. In case of the eyes, it more to do with adjusting exposure than metering, as the pupil dilates and allows more light to enter, but there is still a hint of metering here also. A reverse thing happens when you enter from dark into bright light. For an instant, everything appears white till the brain and eye slowly adjust to the new scene and adjust the exposure and metering apropriately.

The metering on the camera is far far more complex than just adjusting to dark and bright scenes and this is beauty of cameras. You can ask the camera to meter to a particular point of interest in the scene before taking the photograph. There are 3 main types of metering - Average or Evaluative metering, Center-weighted metering, Center or Spot metering. The actual names of these metering would be different on different cameras, but the meaning would be very much similar.

Evaluative Metering meters for the entire frame and decides on an exposure that will try to show as much of the image with correct exposure as possible. This is generally recommended for images of landscape and sceneries and scenes.

Center-weighted Metering is similar to the Evaluative Metering but with the exception that it emphasizes the center area a little more. What this means is that it tries to get the area in the center as correctly exposed as possible even though it may be at the cost of the rest of the image. Although the rest of the image will no suffer too much since it is evaluative metering only. Its just that there is extra weightage on the center area.

Spot-Metering is a more specific form of metering where only the center 10%-15% is metered for exposure. This is used in cases where the entire image frame has a wide contrast/brightness range, but you as a photographer want only the center part of the image with the best exposure. Its not that only the center area is exposed correctly, but the entire image is exposed in such a way that the center area is expose correctly. This could mean that the surrounding areas are exposed correctly or is over/under exposed depending on the contrast/brightness details on the image. Spot meter is the most commonly used form of metering during bird photography and other forms of long distance wildlife photography where is subject is there in the center of the image.

Megapixels

You would have heard a lot of people talking about mega pixels whenever it comes to camera. Whenever it comes to comparing cameras, the first question that someone asks me is "How many mega pixels does that camera have?". In fact I think that is one of the most uneducated question that someone can ask about cameras. Putting it simply, mega pixels don't make a camera. Now lets see what exactly it is.

First let us see what is a pixel.
Pixel stands for Picture Element (pics = pix). A pixel is like a single dot in the image. The image is composed of lots and lots of pixels. Each pixel is of a specific color. Assume that an image has pixels of a single color - red, the entire image will be red in colour. This way in a photo, there are multiple pixels each with a different color and hence a nice colorful image is formed.

A picture is measured in terms of its resolution. The resolution gives the number of pixels horizontally and vertically. So a picture of resuolution 640x480 has 640 pixels horizontally and 480 pixels vertically. Now let us see how many pixels are there totally in the image.

Total pixels-> 640 x 480 = 307200 pixels.

Consider an image of size 1280x1024..
Total pixels -> 1280 x 1024 = 1310720 pixels.

Lets write this in tens, thousands and millions.
1310720 => 1,310,6720 pixels. This is almost equal to 1.3 million pixels.
So, a camera capable of taking images at 1.3 megapixels can take images of resolution 1280 x 1024. Similarly a 5MP camera can take images of resolution 2592 x 1944. This is the basis of megapixels.

Also, in many cameras you will find something called Total Megapixels and Effective Megapixels. The total megapixels is the number of pixel sensing elements in the sensor of the camera whereas the effective megapixels will translate into the size of the image. The reason for this difference lies in the way the sensor is built. In conventional sensors, there are a fixed number of sensors for measuring red, green and blue and this is then processed into the resultant image. As a rule of thumb, if you see 2 different megapixel ratings for a camera, the one that you are concerned about is the smaller number. We will get into details of sensor construction later.

Shutter/Aperture Priority

Some cameras have modes called shutter priority and aperture priority. These are not available in the basic point-and-shoot models but in some of the more advanced models. These modes are usually represented in the mode dial by S or Tv for shutter priority and A or Av depending on the manufacturers wish.

Shutter and Aperture priority modes are a sort of semi-automatic modes. In the fully-automatic mode, the camera will choose the shutter speed and the aperture value automatically depending on the exposure. These automatically chosen values cannot be changed or can be modified using a 'program-shift' feature that some cameras provide.

But now, in these modes, you have the option of choosing the shutter speed or the aperture value on your own and the camera will adjust the other parameter depending on the light and required exposure. For example, suppose the automatic setting requires an aperture of F/5.0 and shutter speed of 1/200s. Now, in the aperture priority mode, I set the aperture to F/2.8. Now the amount of light has increased because of the wider aperture. So correspondingly the shutter speed will be decreased to about, say 1/500s, by the camera, since it is in the aperture priority mode.

Similarly in the shutter priority mode, you are allowed to change the shutter speed value and the camera automatically chooses the best aperture value for a good exposure.

This might not sound very interesting during normal photography, but it makes for very simple shooting when shooting some creative photos.

Focal Length and Angle of View

The last time we had a look at the picture to the left, we learned how to read the aperture specification from how it is mentioned on the lens. As you would remember, there is also another set of numbers on the lens. This represents the focal length of the lens. In this case the figures say 5.8 - 17.4, the readings being in mm.

The layman can translate this directly to the amount of zoom that the camera provides in terms of magnification(2x, 3x etc). The figures indicate that the cameras can zoom from a minimum focal length of 5.8mm to a maximum focal length of 17.4mm. So the magnification that the lens provides is 17.4/5.8 = 3x. This again reflects what is mentioned in the specification of the camera.

Now that we understand the significance of the figures mentioned, we can have a look at what the numbers exactly mean. For this we have to understand what is focal length. Without being too bookish, the focal length is the distance from the lens to the focus of the lens. The focus of the lens is the single point where the light converges after refracting from the surface of the lens. In the case of a fixed lens, this focus point is constant and is determined during the manufacture of the lens and depends on the curvature of the lens. You can read more about focal length and focus from these links - Focal Length and Focus.

Now lets move away from the geometrics and optics and focus on what it means for us as a photographer. As mentioned earlier, each lens has a fixed focal length and this cannot be changed. But cameras have a range of focal lengths as mentioned in the specification. This is achieved by using a combination of lenses. By using multiple lenses, in a straight line, and varying the distance between each of them, one can achieve different focal lengths.

Now most of the focal lengths are compared using the 35mm equivalents. The 35mm film was the most popular film format available and hence all focal lengths are translated into their respective 35mm equivalents. This is because digital cameras have varying sizes of sensors and there has to be a standard for comparisons. In case of compact cameras, the 35mm equivalent focal lengths are mentioned in the cameras specifications and in the case of SLR cameras a focal length multiplier is mentioned. In the case of the W80, the 35mm equivalent focal lengths for 5.8 - 17.4mm are specified as 35mm - 105mm. What this means in other words is that the 5.8mm lens on the W80 provides the zoom equivalent to a 35mm lens on a film camera.

We will take a more detailed look at what this 35mm equivalent means in a later post.

ISO - Light Sensitivity

ISO adds another parameter to the Exposure equation. Till now we had established the relationship of exposure to aperture and shutter speed. From now on we will understand that Exposure is directly proportional to the ISO setting.

ISO is a measurement of the light sensitivity of the camera. Earlier we used to get films with various ISO ratings. A film with a higher ISO is more sensitive to light and on simple point-and-shoot cameras, a high ISO film would be more suitable to shooting in low light than a film with a lower ISO. In essence, that is what a high ISO will help you do - help you shoot in low light.

ISO might sound useful, but, on digital cameras, shooting at high ISO leads to an increase amount of noise in the photo. Noise is nothing but the graininess that creeps into images when you shoot at a high ISO. The noise happens due to various causes, the main reason being the over-heating of the sensing elements in the sensor of the camera. Putting it simply, to increase the light sensitivity of the sensor, more current is applied through the sensing elements. Because of this, the sensory elements are over heated and hence the resulting noise in the final images. Hence high ISO is not all that good for low light photography.

Now why would you need to shoot in low light using a high ISO when you could as well decrease the shutter speed and/or increase the aperture. For one, increasing the aperture is not an option beyond the limits of the lens. You can only increase the aperture up to the maximum value allowed by the lens. So the other option is to decrease the shutter speed to allow more light. This is possible depending on the situation. If you are trying to capture moving subjects(say a moving car) then you cannot keep a long shutter speed as you would end up capturing just a streak of color. Also, a longer shutter speed would give ghosting or blurry images if the photos are taken handheld(as opposed to a tripod). This is due to the induced 'shake' which results in longer exposures. Similarly, if you are capturing a night shot with lights in the picture, then you might end up getting streaks in the image as a result of the light moving around the screen because of camera shake.

In such cases, a compromise over the noise introduced has to be worked out and you would have to decide between decreasing the shutter speed or increase the ISO at the cost of higher noise.

Exposure

Loosely an exposure is defined as the process of light entering the camera and forming an image on the lens/film.

Exposure is a term that is used widely in photography. An exposure is something which indicates that light is passing into the camera through the lens. Usually exposure is quantified by an other term depending on the quality of the photograph.

For example, one of the usages of exposure is in qualifying the image. Consider the set of photos below. Assuming that the photo in the center is how we want our image to look like, you can easily make out that the photo on the left is darker than desired and the photo on the right is brighter than desired. This means that less light than necessary entered the camera to form the image in the left case. Hence the photo was not exposed correctly, in this case the photo is 'under'-exposed. Similarly in the right photo, too much light found its was into the camera and hence the photo is 'over'-exposed. Since the photo in the center is what we need, we would say that this photo is exposed correctly.


So we have now come across the different exposure qualities. Lets say we consider the under-exposed photo. Why is the photo under-exposed? It could be because the shutter speed was too fast, or the aperture was too small or a combination of both. Similarly the over-exposed image was a result of the shutter speed being too slow, or the aperture being too wide or a combination of both. From either cases we realize that exposure is a resultant of the shutter speed and aperture. Exposure is directly proportional to aperture and inversely proportional to shutter speeds. This is the mathematical definition of exposure.

Mathematically,
Exposure = Aperture / Shutter Speed.
[Note: There might be other factors affecting exposure, but this is the relation of exposure with aperture and shutter speed]

To achieve good exposure one must choose an ideal combination of aperture and shutter speed. In the point-and-shoot mode, the camera itself has an automatic control mechanism where it would choose the aperture and shutter settings for correct exposure. In little more advanced cameras there is a shift mechanism whereby you can set an increase in shutter speed and corresponding decrease in aperture or a decrease in shutter speed and corresponding increase in aperture. You might wonder where is the necessity to modify the automatically chosen shutter and aperture settings. This part we will cover in the posts on how to get creative with aperture and shutter. For now its important to understand the relation of Exposure to Aperture and Shutter-speed.

The other usage of exposure is 'long'-exposure and 'short'-exposure. Long-exposure refers to taking a photo keeping a longer shutter speed duration while short-exposure is one where the shutter speed is very high. The reasons for long and short exposures will be looked at in the posts that deal with creativity.