Archive for category Tutorials
HDR Photography
HDR (High Dynamic Range) photography refers to increasing the color range of a photo.
Our eyes are an amazing contraption. They quickly adapt to many lighting conditions, and the brain kicks in whenever help is needed. In certain conditions, your camera will fail dramatically (or just fail, depends how you look at it), be it a camera mounted on a spy pen or a new Canon 5D Mark II. The conditions I’m referring to are ones which include very bright and very dark areas. Correct exposure to the dark areas will burn the bright areas, correct expose to the bright areas will result in very grim dark areas.
Consider the following photos of average exposure, correct exposure to bright areas and correct exposure to dark areas:
 People's Park, Shanghai - EV 0 |
 People's Park, Shanghai - EV -2 |
 People's Park, Shanghai - EV +2 |
So what do we do? We take multiple shots with EV compensation! The photos above were taken at aperture priority with an aperture of f/16. The first image shutter speed determined by the camera for correct exposure: 1/640 seconds (high ISO used). For the underexposed image, the shutter speed went up to 1/2500 seconds (-2 means 2 stops under, so multiplied by 4). The overexposed image’s shutter speed was 1/160 seconds. Notice how the first photo is nice, but it loses details which are found in the other 2 photos (at a cost of ruining the remaining details of the image).
Next, we combine the photos into a single picture, by taking the correctly exposed areas from each photo. You can do it in Photoshop (many tutorials online) or use a program doing that thing exactly. I achieved the following result using the trial version of Photomatix (so forgive the watermark):
People's Park, Shanghai - HDR
Detailed building from the underexposed photo, details in the tree and water from the overexposed photo.
Check your camera user manual, usually it will offer you an auto-bracketing feature, which will take a normal photo when you first release the shutter, an underexposed on the second release and an overexposed on the third. You can also determine by how much do you want the EV compensation to be. By the way, using a tripod is recommended.
Composition Rules
It has come to my attention that every beginning photographer has to learn some very basic rules:
- The Rule of Thirds explaining that a picture should be divided into 3 by horizontal and/or vertical lines.
- The Golden Ratio referring to a ratio used since the days of Leonardo De Vinci and is said to be found everywhere in nature.
- The Rule of Diagonals about having long diagonals across your photos.
- And probably many more…
Some rules are meant to be broken.
And now for something completly different: a hoopoe playing with it’s food…
Image Exposure – Part 2
In my previous post, I’ve explained about how the aperture and shutter speed affect the resulting image exposure. It’s all true. But not entirely. There is one last thing affecting the exposure:
ISO (or film sensitivity) affects the sensitivity of your “film”. I remember buying film for my old camera, having to choose between Kodak 100, 200 or 400. Completely unaware of the difference, I’d choose the cheaper one. The ISO determines the sensitivity of the sensor to light. The more sensitive (higher ISO), the brighter the image will be. This allows you to “push” beyond the limits dictated by aperture and shutter. I usually shoot at higher ISOs indoors or at night, or basically, when lighting is scarce.
My post of night photography shows a picture taken at night at 1/6 seconds at the maximum aperture f/4.5 and highest ISO settings: 1600. Had I used a lower setting, such as 800, I would have had to double the exposure time (since it’s half the film sensitivity). That photo at 1/3 of a second would have been quite blurry I guess.
Downside of high ISOs? Image noise. Lets compare the extremes: ISO 100 opposed to 1600:
 Bottle - ISO 100, 1/8 sec, f/5.6 |
 Bottle - ISO 1600, 1/125 sec, f/5.6 |
So we can photograph at the same settings at higher shutter speeds (or smaller aperture) at higher ISOs – but at a cost…
The last thing affecting the exposure, is EV compensation. You can manually brighten or darken your photo. Set the EV compensation to +1, -0.3, +2. Depends on what your camera allows. EV +1 means the image will be brighter by one factor (equivalent to doubling the exposure time, or the aperture size). You can also take a photo at auto bracketing. This will take 3 consecutive photos: one at regular exposure, one at negative EV compensation (underexposed) and the last at a positive EV comp (overexposed). I took a nice sample going to lunch the other day:
 EV compensation - normal |
 EV compensation - underexposed |
 EV compensation - overexposed |
My thanks to the two lovely models I met on the street. And that’s all I have to say about that…
Image Exposure – Part 1
Image exposure is a term describing the light entering through the lens of your camera and hitting the sensor. Basically – we’re talking about the total brightness of a picture. Good image exposure is subjective, but lets look at the extremes:
- Photographing the sun at midday will result in a very bright image which we call an overexposed image.
- Photographing with no flash or external light at nighttime will usually result in a dark image – an underexposed image.
If you recall the first lesson, the two things that control how much light reaches the sensor are shutter speed and aperture.
Longer shutter speed means the shutter remains open for a longer time, and more light will reach the sensor. Larger aperture means the hole leading to the sensor is bigger, and more light will reach the sensor. So fast shutter speed will require a larger aperture, and slow shutter speed – smaller aperture. I know I’m being repetitive, but I still need to think about it to remember this. So writing this over and over helps me remember 
I decided to use my Mc’Donald’s Happy-Meal dog who is sitting loyally near my monitor to illustrate this:
 1/15 seconds, f/11 |
 1/30 seconds, f/8 |
 1/60 seconds, f/5.6 |
Yes, my lens require cleaning. I cleaned them, but I was too lazy to take another go at these photos. I took all of these in Shutter Priority (Tv – time value) mode, which allows you to set the shutter speed, and the aperture is determined by the camera. As you can see, the images look pretty much the same. The longer the shutter speed, the smaller the aperture (light enters longer, camera selects a smaller hole to achieve same exposure) and the other way around.
When you photograph in Aperture Priority (Av – aperture value) mode, you can control the aperture, but the shutter speed is determined by the camera to achieve optimal exposure.
There is also a Manual (M) mode allows you to select both aperture and shutter speed.
Important thing to remember is this: your camera has limits. A minimum and maximum aperture and shutter speed. If you try to shoot something at a very high shutter speed, but light is insufficient, the camera won’t be able to set a big enough aperture, and you’ll get a dark (underexposed) image. Shoot outside in midday at slow shutter speed (to get a blurred effect for example), and the camera might not be able to select a small enough aperture, and you have a very bright (overexposed) image.
Again, I’ll resort to samples with Lucille, where the aperture of the kit lens used ranges from f/5.6 to f/32. So adjusting the shutter speed to high enough and low enough values produced the following lovely results (due to aperture limits):
 Underexposed: 1/125 seconds, f/5.6 |
 Overexposed: 2 seconds f/36 |
This is the basic idea. There’s more, but I’ll save something for the next exposure post.
Happy correctly exposed photographing!