Wednesday, October 5, 2011

Photography basics-2

When I bought my first DSLR - Sony A200, I was using it in the auto mode for a long time. I was also making fun of my friend who always keeps his camera in the manual mode and struggles in changing the settings to match the scene. My question was simple, if the camera can find out what is the best setting for a given scene, why bother fiddling with that and waste your time learning what those settings are for? Very soon I realized that I was wrong, but I still don't keep my camera in full manual mode always. There are a lot of places where you just can't go with the default camera settings. For example you want to take the photo of a waterfall showing how the water is flowing. Or you want to take a portrait picture with blurred background sometimes and focussed background some other times. Without knowing the settings, you can't tell your camera how to capture these specific scenarios. So, it becomes essential to know how to use the camera controls rather than leaving the full control to camera and it deciding how the photos should look like.

Every camera has hundreds of settings, I haven't looked at most of them. So I will only try to cover some of the basic concepts that helps in understanding few of them.

1. Sensor - sensitive plate that absorbs the light and transforms it to pixels, equivalent of film in the older camera
2. Exposure - Amount of light allowed to fall on the sensor for a good photo
3. Depth of field - Distance between nearest and the farthest object that is acceptably sharp in the view
4. Aperture - size of the hole in the lens that controls the amount of light entering the sensor
5. Shutter speed - How fast the shutter (placed in-front of the sensor) opens and closes exposing the sensor to light
6. ISO - sensitivity of the sensor

In simple words, the process of taking a photo is to make the light rays of the subject fall on the sensor. The right amount of light that needs to be collected by the sensor is called as exposure. If the subject is exposed too long, the picture looks washed out, also called as over exposed photo. If the subject is exposed too short, the photo looks very dark, called under-exposed photo. If you are able to determine the right amount of light for the subject, the task of taking the right photo is almost done. All cameras generally have a built-in light meter, which determines the right amount of exposure for a given subject. Once the right exposure is determined, that is converted to actual settings by changing the aperture, shutter speed and the ISO. Light meter generally gets the exposure right for all the cases except for very bright and very dark scenes. I am not sure how or on what basis the camera auto mode balances between these three settings to get the right exposure. The balance of these three parameters is very important as they also affect some other parameters affecting the final result. So these three are commonly called as photographic triangle.

Aperture is the hole in the lens that controls the amount of light entering the sensor. A lens marked as 18-250mm f/3.5-6.3 has a focal length range of 18mm to 250mm and aperture size of 3.5 at 18mm and 6.3 at 250mm. Aperture is actually expressed as f/aperture. That means, lower the aperture number, higher is the lens opening and more light entering the sensor. Higher the aperture number means lower the hole size and light entering the sensor is also minimal. The number 3.5-6.3 on the lens represents the maximum aperture size for that focal length and can go as low as f/22 or lower based on the lens. Apart from the light, aperture also controls what is called as depth of field, which determines how blur the background(or non focussed) objects will be compared to the subject. While taking the portraits or some specific object, you might want to give the full attention of the viewer to the subject by making all other elements in the view blurred. This can be done by choosing a higher aperture (lower aperture number). Similarly, if you want your photo with a nice background in a famous location, you need large depth of field to keep the foreground, background and your subject focussed in the photo. This needs a small aperture (ie large aperture number in the camera). The depth of field can also be controlled by the focal length. In general, higher focal lengths give shallow depth of field.

Shutter speed determines how long the shutter will be open thereby exposing the sensor to the subject. The longer the shutter is open, more light that enters the sensor exposing the subject longer. If you want to freeze the motion of a subject, you need to keep a smaller shutter speed like 1/2000 or smaller. Bird photography, wild life and sports generally need very small shutter speed. If you need to capture the motion, you need to keep higher shutter speed, like flowing water or waterfall.

ISO is probably more easier to decide, which changes the sensitivity of the sensor to collect the light. Higher the ISO speed,  faster the camera collects light but it also adds more noise to the photograph than the lower speeds. So, it is always better to keep the camera in lower ISO speed when there is enough light and increase it only in tight lighting conditions like indoor or night photography.

So, putting a camera in manual mode is all about deciding the right aperture, shutter speed and ISO for a given scene. Understanding these three helps to determine the best settings for a given scenario. However, you may not have to keep your camera in manual mode always changing all three settings. Instead it would be often easier to keep it in Aperture(A) priority mode and set the aperture, which automatically determines the shutter speed for the right exposure. In general most of the lenses have a sweet spot, generally at around f/8, which is suitable for most of the scenes. You might have to change that when you need to control the depth of field. Similarly, when your aim is to capture the motion or freeze the same, you could keep the camera in shutter priority mode which selects the right aperture. When you are not satisfied with both, you can turn your camera to manual mode.


Kishor said...

If it was me you mentioned using manual mode, I now mostly use the Program mode for most shots apart from where you need full control over shutter speed and aperture.

Sathisha said...

Yes, its you only :)

Sriram said...

Liked it.. Hope you cover White balance in your third part!