Wednesday, December 07, 2011

Photography for Elearning Developers - Understanding Exposure

Between the last post and today, I had a great time at Thattekad - one of India's finest bird sanctuaries down south. I can't say it was the best photography tour - grey weather, rain and dark clouds never make for a good mix. I did have a fascinating birding trip, having spotted 110+ bird species during those three days. Along the way, I got some good photographs but not too many to be frank. I'm hinging my photography fortunes on the next few trips this winter - hopefully my luck will come good somewhere.

Coming to the topic of today's blogpost, you may remember that in my last blogpost I'd explained how to choose a new camera for yourself. In today's blogpost I'll follow that up with what I consider the most crucial part of photography - exposure. Simply put, exposure indicates the total amount of light that your camera receives during the time that you record a photograph. When your picture is optimally exposed, you get a great picture. In photography parlance, an underexposed image is usually dark and conversely an overexposed image is usually too bright and white. Well, not all the time - but we'll come to that later. Let's first look at the three different parameters that actually affect the exposure on your image.


Aperture on your camera lens indicates how wide your lens is open when receiving light. The wider open your lens, the more light it can take in - the narrower the opening, the lesser the light. Simple? Your camera indicates your aperture setting using what we call an f-stop. The confusing thing to remember though is that the larger the number, the narrower the aperture. This is because we express aperture as a fraction of the focal length. f/1.8 therefore is wider than f/5.6.

Now why would you like to control aperture? Firstly of course, a wider aperture gives you more light for your frame which is always a good thing. That aside, adjusting your aperture gives you the opportunity to play with the depth of field on your picture. Depth of field refers to the depth of the picture after which the camera blurs out the details. Remember seeing those pretty portraits where the background is a beautiful blur? This is a result of playing with the aperture. So here's the trick - a wide aperture will usually result in a shallow depth of field. A narrow aperture on the other hand will capture a large part of the image in a sharp fashion. So for portraits you can go with wide aperture. With landscapes and interiors you could go with a narrow aperture. Take a look at the above pictures for reference.

Shutter Speed

Shutter speed refers to the amount of time a camera's shutter is open when you capture an image. Think of a tap and a glass to fill. If you opened the tap fully your glass will fill in a jiffy. On the other hand if you just let the tap drip a drop at a time, it'll take you much longer to fill the glass. This is the relationship between aperture and shutter speed when it comes to aperture. If your tap of light is fully open you can go with a fast shutter speed. If your tap of light is down to just a drip you'll need a longer shutter speed to fill your glass of light. Simple?

Here's why you may want to control your shutter speed. When you shoot at a high shutter speed you freeze action in that split second. When you shoot at a lower shutter speed you get the opportunity to capture details in the poorly lit scene or capture motion using creative blurs - like the silky smooth waterfall in the above picture. The above pictures will help you see how shutter speed can help you capture different kinds of photographs.

ISO or Sensor Sensitivity

What if your tap was down to a drip and you still wanted to fill your glass quickly? You'd have to cut some corners right? You could potentially fill the glass with sand such that it takes only short amount of time to fill the glass! Yes, yes you make the water dirty - but you do fill the glass, don't you. This is how ISO works as balancing factor for exposure. ISO defines how sensitive your imaging sensor is to available light. So ISO 100 indicates low sensitivity while ISO 6400 indicates very high sensitivity.

Where could adjusting the ISO come in handy? Think about a situation where you're shooting a cityscape at night - handheld. If you shoot at low ISO, you'll need a very slow shutter speed. Here's the catch - slow shutter speeds introduce blur because very few people can keep their hands steady for more than 1/60th of a second! In such a situation, if you shoot at ISO 100 you just won't get a sharp picture. On the other hand you can go with a sensitivity of ISO 800 and you'll most likely get a sharp picture.

Now here's the other catch - remember the sand in the glass? The higher the ISO, the lower the quality of your image. In the film days you'd notice this in the form of what they called film grain and in the digital world you see it in the form of image noise. So the bottom line is this - a high ISO is the arrow in your photography quiver which you want to use only if absolutely necessary.

How do you control Aperture, Shutter Speed and ISO?

While most serious cameras have a manual mode where you control everything, it's usually not the best idea unless you're shooting in a very controlled, studio type setting. You're best off controlling either Aperture or Shutter speed and letting the camera control the other. If you're using a DSLR, then you'll perhaps know the modes to control these as Aperture priority (A on Nikon, Av on Canon) and Shutter priority (S on Nikon, Tv on Canon). All you need to do is pick the parameter you want to control, select the ISO you're willing to live with and let the camera help you along from that point.

What mode do I shoot on? Well as most photojournalists would say, "Aperture priority, f/9 and stay there!". Well not quite - I select modes based on the need of the photograph, but for the most part I shoot in Aperture priority since that allows me to control how much of the picture stays sharp and how much blur I need.

A Photo Case Study - Ceylon Frogmouths

For the last year or so, I've been waiting to see the Ceylon Frogmouths. These birds are some of most elusive species to spot in the wild. In fact, I was looking up Wikipedia and found that from the Batrachostomus genus only bird that they have photographs for, are the Ceylon Frogmouths.  These birds have excellent camouflage. They're hardly 23 cm in size and they choose their homes in dark, thickly forested, leafy areas. Since they look like dry leaves and branches they completely blend in. You could be a meter from them and still not be able to see them. The reason why we can actually find them in some spots of India is particularly because some birders know their roosting spots and end up guiding folks like me.

Now to this photograph - the tropical forest was very dark. We were struggling to see the frogmouths with naked eyes - through the camera it was even tougher. I proceeded to shoot at the widest aperture my camera offered. However at f/5.6, the shutter speed of 5 seconds was just unmanageable with a big lens, handheld. I kept upping the ISO until I reached a shutter speed of 1/30th of a second and then pressed the shutter. At an ISO of 6400, the picture isn't as sharp or as high quality as I'd like it to be, but I want to think it was the sharpest I could have got in that environment. I could have perhaps gone to ISO 12800, but that would have brought down the picture quality even further. In any case I hope this adventure of a photograph helps you see how ISO, shutter speed and aperture play together to help create the right image.

I hope today's blogpost gives you a basic sense of exposure for your photographs. I am mindful that I'm not focussing on elearning-only situations with my examples and that's deliberately so. I'm guessing that if you can use your camera effectively in a life situation, the ability to do so for elearning will come automatically. In the next blogpost, I'll touch upon some simple tips related to colour and format choices in photography. Stay tuned until then - cheers! Is there other stuff you'd like me cover on this blog? Let me know by dropping your comments on this post.
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