Essential basics 1 - Exposures

Before going into exposure, it's worth while taking a step back and understanding how your camera works.

A camera is essentially a tool to capture light, and light is manipulated via a set of glass in the lens to create photographic effects such as magnification, etc.

Observe the diagram below (forgive my crap drawing, hehe),


Light reflected off a subject travels through the aperture and a set of glass that acts as lenses, ending up on the sensor where the light information in then picked off and converted to digital images.

For this article, we will discuss about exposures. You should strive to get correctly exposed photographs. A picture can either be underexposed, correctly exposed, or overexposed. And underexposed picture appears dark while and overexposed picture appears overly bright. Too much light entering the sensor leads to overexposed images while too little leads to underexposure.

Exposure is determined by three variables, known by some as the triangle of exposure.

The variables are:

1. Aperture
2. Shutter speed
   
3. ISO sensitivity
   

• Aperture is essentially the gate to the lenses, the larger the aperture opens, the more light enters. (I.e, the larger a gate opens, more people can pass through them at any one time).
• Shutter speed is essentially how long the gate stays open. So logically the longer the shutter speed, the more light is able to enter and reach the sensor.
• Finally, ISO sensitivity is just how sensitive the sensor is to light.

Behind 'Auto'

Exposure Compensation
In the 'auto' setting, the camera does all three automatically. It 'meters' the subject (i.e, calculates the exposure) and then adjusts the variables to achieve the correct exposure.

However, there are some circumstances when the camera fails to 'meter' correctly. In general, two situations will almost always cause the camera to fail:

1. Subject is too white. When the subject has too much white in it, the camera gets confused and tries to compensate the whiteness by decreasing the exposure. It will result in an underexposed picture. A good example is taking pictures while skiing, with snow in the background, or during weddings, where everyone dresses white.
   
2. Subject is too dark. When there's too much black, such as taking a picture against a dark wall, taking pictures when everyone dresses in suits. The camera thinks the scene is darker than it actually is and tries to increase the exposure.
   

To correct this, you'll need to override your camera's automatic metering by doing 'exposure compensation'. It's like trying to tell the camera "dude, you're wrong".

In most cameras, the exposure compensation setting should look like this. The button is usually the +/- button seen to the left of the picture. Just move the cursor left (more -ve) to the "Zero" or right (more +ve) to undercompensate or overcompensate.

In general:

• In white places overcompensate.
• In black places undercompensate.

The decision on how much to set the exposure compensation is partly guided by the histogram, and partly guided by what you wanted the picture to end up as.

The histogram looks like this:
It usually is a bell curve with the apex of the curve more towards the left or right depending on how bright or dark the picture is.

More importantly is the ends of the curve. You'll want to adjust the exposure compensation so that the ends of the curve touches the end of the graph.

In this example, the picture is underexposed. You should increase the exposure compensation in the camera. This would shift the whole curve to the right and finally corrects the exposure.

On the other hand, an overexposed picture will have nothing on the left side and you simple need to decrease exposure compensation.

Here's an explanation I shamelessly copied from another site. hehe

The great thing about a digital camera in this aspect is that you can do this live while preparing your shot. The preview screen can usually overlay this information.

For the rest of us however, the only way to get it right is through trial and error.

You can, if you wish do this during post processing using any programs in the market, including free programs like Picasa or more expensive and powerful ones like Photoshop CS4. The good side is you don't have to worry too much about exposure while shooting, the bad side is that doing this usually increases the noise levels of the pictures and you might loose some details.

It is safer to underexpose that to overexpose. When overexposed, the information of a picture is lost as 'highlights'. The part of the picture looks purely white and there is no way to recover that data through post-processing.

Beyond 'auto'

This portion of the article may not be too relevant to digital camera users. However, a knowledge of some of this may help in your photography.

Most prosumers and dSLRs come with manual and semi manual functions. Using these functions gives you more control of your scene and allows you to be more creative than simply point and shoot. Although some may find it difficult to understand, here's some simple explaination on how it all works.


As you can see above, Nikon labels the manual function as M for manual, A for aperture priority and S for shutter priority. Canon's a little less intuitive with M, AV and TV respectively. In manual --> you can set both the shutter speed and aperture manually

• In A/AV --> you set the aperture manually and the camera sets the shutter speed automatically (you can use exposure compensation here since the camera is still doing automatic metering)
• In S/TV -->you set the shutter speed and the camera automatically sets the aperture.
  

In all three cases (and auto), you can decide on which ISO sensitivity to use.

The next question is, what settings should I use?
Look at the triangle of exposure again. In general, increasing one variable increases the overrall exposure, therefore another variable needs to be decreased. Which variable you increase depends largly on what you wanted to achive and what tradeoffs you want to sacrifice.

Aperture is measured as f-stops. The larger the number, the smaller the aperture.

picture taken from http://jackarcestudio.com/?p=291

• A wider aperture (f2.8, f4.0) gives you more light, but less depth of field.
  
• A narrow aperture gives you less light, but more depth of field.
  

picture taken from http://tomasellodesign.wordpress.com/2009/04/20/little-tip/

A smaller depth of field allows you to focus on the subject and blurs the background. This allows the viewer to concentrate on what you really want them to see and creates a nice creamy background as a backdrop. This effect is called 'bokeh'.

This picture of the bee for example shows a clear bee and blurred backdrop.

Shutter speed:
Shutter speed is measured in seconds and fraction of seconds.

• A faster shutter speed allows less light (less exposure) but freezes movement. This allows sharper images to be taken and also allow you to creatively freeze objects in midair, freeze sports, etc.
  
• A slower shutter speed allows more light (more exposure) but it leads to blur and camera shake if no tripod is used. It is more suitable in night photography, night scenery, fireworks, etc.
  

ISO sensitivity:

• ISO sensitivity is how sensitive the sensor is for light. The more sensitive it is, the more light you can get and it allows for a faster shutter speed and narrower aperture to be used. It sounds all good but it also translate directly to more noise in the camera.
• Noise in some aspect is good, it gives a nice texture to black and white photographs.
• Typically use 200 ISO for normal light, about 400 ISO for indoors with adequate lighting and in dark areas, you can push the ISO as high as you like within limits of your camera and the noise produced.
  

In conclusion, before you shoot, decide what effect you want (freeze, scenery, less/more noise) and select the appropriate settings.

Feel free to drop by any questions in the comments area. Thanks for reading!

Essential basics of photography

From now onwards, I will be discussing about the very basics of photography. This should allow users of all three types of cameras to gain better understanding of what actually happens within your camera everytime you try to take a picture. Briefly, the two main topics are exposure and composition.

Selecting SLR cameras

While buying consumer or prosumer cameras are pretty straightforward, selecting a suitable SLR require a little more thought. This is because there are lots of different camera bodies and lenses to choose from and they don't come cheap.

Before commiting yourself to a SLR, ask yourself whether you really need one. If you are just going to get an SLR with just the standard kit lens (the lens that came with the camera) and not thinking of getting anything else, often a prosumer camera will be a suitable choice. The kit lens, while good, is not useful for many situations, such as close-up or macro photography. In some situations, a good prosumer can outperform a low end SLR at a lower price.

Additionally, if you're not going to upgrade or add more gear, its rather pointless to own a SLR. In my opinion, unless you are really serious into photography, go for prosumers.

These are the things you need to consider:

1. Budget

The amount of equipment you can buy when going into the SLR path is endless, so you'll need to know how much you can afford.

From this budget, you can decide what combination of equipments you can acquire.

For most beginners, a budget of $2000 should be a sufficient investment.

2. Purpose

There are many sub-specialities in photography, and more importantly so when considering SLR since the lenses are quite specialised.

Think about what you will do with your camera, is it:

• portraits
• macro/close-up
• sports
• events
• nature
• scenery
• holidays

The list may go on but these are the general ones. Each of these require their own set of lenses and other equiptment. Having said that, some of the equipment can be shared between them.

3. Research

With an idea of how much you have to spend and what you are going to spend it to do, you can now begin browsing for your first SLR. It is essentially a similar process as discussed in the previous article.

I will not discuss exactly which model or brand you should go for, since it is really a matter of preference. Instead, I will discuss in general the principles of a SLR so that you'll understand the terminology.

4. Brand

In general, there are 4 major brands that I know of that sells good SLRs.

1. Nikon
2. Canon
3. Sony
4. Pentax

There are others of course, but I do not have enough experience with them. I personally own a Nikon and have friends that uses Canon cameras. I feel that if you go for Nikon or Canon, it'll be a good choice because there are many people who uses them and you'll be able to talk with others about your equipment or even share lenses with your friends. These brands are also in the market for the longest. Sony and Pentax are good because the camera bodies come built-in with image stabilisers (nikon and canon places the component in the lens instead).

In general, you'll need to decide two components of your SLR.

The camera body,

and the lens.

Its really simple, the lens takes in the light and alters them (magnify, etc) and the body has the sensor which receives the light and convert them into digital information.
BODY

In general you can divide the body into three generations:

• First generation
• Second generation
• Third generation

It gets a little confusing (and stupid) here. For nikon, the first generation cameras has 2 digits (D40), second generation has 3 digits (D300), and third generation has 1 digits (D3). Now there's a new nomenclature with 4 digits (D5000, D3000), which is essentially a first generation camera. The Canon cameras are less confusing, first generation has 3 digits (400D), second has 2 digits (40D) and third generation has 1 digit (5D).

In general, the higher the generation, the better the body are in terms of dynamic range (discussed later), speed of action, megapixels and other small details. They are also significantly more expensive as you move up a generation.

For our consideration, a first generation camera is sufficient as a beginner. There are other stuff like full frame and 3/4 frames but that's complicated. A first generation camera is almost usually a 3/4 frame camera.

LENS

This is where your earlier consideration comes into play.

In general when buying lenses, these are the factors that comes into consideration:

1. Focal length
2. Maximum aperture
3. Vibration reduction
   

Focal length:
Focal length is pretty much how much you can zoom the lens. the numbers vary from 10mm to 500mm and pretty much a smaller number is how much you can zoom out (wide) and the larger number is how much you can zoom in (tele).

For example:

The Nikon D90 kit lens:


The markings you can see is: AF-S NIKKOR 18-105 MM 3.5-5.6G ED.

For this lens, the focal length is 18-105mm. 105mm doesn't really give you much a zoom, a good zoom should be about 200mm in a crop sensor. 18mm is wide enough for scenery, but a real wide angle lens is about 10 or 12mm wide.

Note: There are also 'prime' lenses, which are lenses that does not allow zooming, they are fixed lenses. A good cheap prime lens is the Nikkor 50mm F1.8 prime lens.

Lastly, there are also all purpose lenses for those lazy to change lens on the go, they are usually 18mm-200mm so cover both wide and tele. However, they usually perform less better in terms of colour reproduction, sharpness and other factors.

Maximum aperture:
If you look at the lens again, there's this 3.5.5.6 marking on it. That's the maximum aperture. Significantly, when they place the max aperture from one number to another, it means when you zoom in, the maximum aperture decreases. Basically the larger the aperture, the more light you can take in at night and the more bokeh you have. (will be discussed in detail later).

Note: the larger the number, the smaller the aperture.

In general, a good lens should have a fixed maximum aperture at F2.8. The Nikkor 50mm F1.8 prime lens allows a max aperture of F1.8.

Vibration reduction:

Vibration reduction VR (or image stabiliser in Canon) is an important aspect. It reduces camera shake and allows better pictures at night. It is also important to consider in telephoto cameras since shake is amplified the more you zoom in. However, these lenses usually cost more.

Brand

One other thing to think about when choosing lenses is the brand. In general there's the brand of the manufacturer of the chosen body (canon, nikkor) and there's also 3rd party lenses.

3rd party lenses are generally cheaper but in terms of performance may not match that of original lenses. However, there are some instances where 3rd party lenses outperform the original.

The better known brands are:

1. Tamron
2. Sigma
3. Tokina

I personally use a Tamron lens and it has performed wonderfully.

So in general:

• portraits --> long focal range, large aperture + external flash
  
• macro/close-up --> large aperture, specialised lenses + external flash
  
• sports --> very long focal range (300-500mm), large aperture
  
• events --> average focal range 200mm, large aperture
  
• nature --> very long focal range
  
• scenery --> wide angle (10-12mm, 17mm)
  
• holidays --> all purpose lens (17-200mm)
  

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If you don't want to commit to any particular style, you can go for something like:

Nikon D90 body
Tamron 17-50mm F2.8
Nikkor 55-200mm F4.5-5.6
External flash SB-600

That would cost a little more than AUD2000 but you can do most things with that.