To be honest; the reason you used the flash sync speed was because in most cases it was a mechanical speed, just in case you had one of those new fangled SLR’s that use electronic shutter. But besides the obvious dependency on a charged battery, there are other differences between film and digital cameras.
If you have ever shopped for a digital camera you have no doubt heard one of the key buzz phrases, “35mm equivalent”. This means that the optics are not exactly the same. Since the 35mm SLR camera has been the standard for the last 50 years, that’s what they compare it to. The difference between the two is a ratio of 1:1.4. Simply put, a 35-200 zoom on a digital camera would be like having a 49-280 zoom lens on a traditional 35mm camera.
The main reason the optics are different is because the sensor (the device that actually reads the light) is also a different size. Film cameras use a film sensitive to light that is placed directly behind the lens. When the correct exposure is calculated, that image is literately burned into the film. Digital cameras, on the other hand use a sensor; that also sits behind the lens. This sensor is made up of millions of individual points that each represents 1 pixel. Once the sensor has gathered the information for each pixel it then transfers that data to a digital media card of some type (which can be used again and again.)
Generally digital cameras use sensors that are smaller than the 35mm film used in older cameras. The Depth of Field changes with the size of the sensor, the smaller the sensor the higher the depth of field. The reason they are made the sensor smaller is generally a cost factor to the manufacturer.
The sensor is the physical device that gathers information about the quality of light coming into the camera. The process or “how” it goes about gathering that information is referred to as “metering. The human eye can see the world around it with a range of about 16 f-stops; camera meters on the other hand, only have a range of 5 f-stops at any given time. This is why camera meters are calibrated for “mid range” exposures of 18% gray, because 90% of the time that is as close as we will get to what the human eye can do. It’s not a fault that the camera can not see as good as you do, it’s simply a fact of life.
There are basically only three types of metering systems. They are:
- Spot Metering
- Center-Weighted Metering
- Matrix Metering
Spot metering as the name indicates only reads a small spot or portion of the overall image (usually 1% to 3%). This type of metering is useful in any situation where the lighting is extreme. Backlit subjects, macro shots, or even pictures of the moon can benefit from this type of metering. This type of metering is usually found on the more costly upper end cameras.
Center-Weighted metering averages the overall scene with an emphasis on the center area of the frame. Usually this type of meter bases its reading with 75% of the light hitting center frame and 25% for everything else. It assumes that most people place their subject dead center, most of the time. It is worth noting that most center weighted systems have a greater sensitivity in the bottom half of the frame; to avoid an overly contrasting sky from throwing off the readings. This type of system is by far the most common used in digital cameras today. Even the higher end Digital SLR’s use this as their default setting.
Matrix Metering splits your image up into anywhere from 3 to 16 metering zones and evaluates the different zones to come up with one over all reading. In this process of evaluation it takes into account factors like: subject size, position, distance, point of focus, over all lighting, color and more. This system uses a microchip which has been exposed to thousands of different picture-taking situations. It is by far the most complex and the most accurate metering system to date. It is also usually found on the higher end Digital SLR’s.
I have used the word “digital” several times, but do not be deceived. These are the same type of metering systems used in traditional film cameras as well. The only other known way of reading light has to do with “reflected light” verses “surface light”. Most meters in the camera are reading reflected light (IE the light that is reflected off the main subject and reaches the camera.) Every so often you will see someone with a hand held light meter that will go right up to the subject and read the light that falls on the surface of that subject. Some photographers still debate which way is more accurate. The idea of the “Spot Metering” should accomplish the same thing, but for many photographers (fashion photographers in particular), the separate meter seems more standard.
With these points in mind, consider not only the differences but the similarities as well. All of us have our favorites; Canon, Nikon, Kodak. Some choose digital, some choose film. The things to remember are what we all need to get a great shot. Things like composition, leading lines, framing, and the rule of thirds are much more important to our success as great photographers than the physical tools we use to accomplish a great shot. On the other hand, knowing what your particular camera or metering system can or can not do, let’s you know if you have the right tool for the job.