When choosing a camera, there are many factors to consider. At the top of most peoples’ lists are resolution, frame rate, and recording format. One may also consider the recording medium and lens mount, especially if they have already invested in a certain type of memory card or collection of lenses. Another factor, which has received more attention in the past 10 to 20 years, is sensor size. When I started in video production in the late 1990s, you were lucky to have a 1/3-inch sensor in your “prosumer” camera, and professional cameras were sporting 2/3-inch sensors. Today, we swim in a sea of sensor sizes: Super 16mm (S16), Micro Four Thirds (MFT), Super 35mm (S35), and Full Frame (FF). And these are just the sizes with standard names. Manufacturers are developing sensors of all sizes in between these today.
The most important thing to remember in the midst of the marketing hype: a larger pixel count (or more K’s) does not mean a larger sensor.
So how much does sensor size matter? How much weight should it have in your decision-making process when purchasing a camera? How does it impact lens selection? As with all the variables—price, size, resolution, frame rate, etc. —the answer is, “it depends.” To determine how much it matters in your use case, it is important to understand what impact sensor size has on the images your camera produces.
Depth of field
First, as a bit of a follow-up to my article, “A Deeper Understanding of Depth of Field” (https://www.churchproduction.com/magazine/a-deeper-understanding-of-depth-of-field/), sensor size is one variable in controlling depth of field that we can only really affect through our purchase decision. Granted, some cameras may use different portions of the camera’s sensor based on the shooting resolution you choose, but for the sake of this article, I will focus on the overall sensor size. It boils down to this: a shot of the same size on two cameras with different-sized sensors will result in a shallower depth of field on the camera with the larger sensor if all other things – other than the focal length of the lenses – are equal. Wait, why did I hint at the fact that the local lengths of the lenses on the cameras will be different? Well, because how the sensor size interacts with the lens is really the heart of the matter.
The focal length of a lens is always the same no matter what lens mount it has or what size sensor the camera has …
Focal length
The focal length of a lens is always the same no matter what lens mount it has or what size sensor the camera has. This means that a full frame 105mm EF lens on a Canon 5D is creating the same-sized image as a 105mm micro four thirds lens on a Blackmagic Pocket Cinema Camera 4K (BMPCC4K). When I say “creating,” I am referring to the image being projected out of the back of the lens, or what is known as the image circle.
The difference in image composition that will be evident is a result of the different sensor sizes. The smaller micro four thirds sensor will only record the center of the 35mm image, resulting in an image that appears zoomed in, closer, or cropped depending on your preferred terminology. The larger full frame sensor will record a comparatively wider image. This is why you might hear the term “crop factor” thrown around when talking about various cameras and their respective sensors. If you were to place the full frame 35mm lens on the “cropped” BMPCC4K with a non-speed-boosting lens adapter, you would end up with the exact same image as the micro four thirds lens. 35mm is 35mm.
85mm Lens @ f4 Full Frame Sensor.
85mm Lens @ f4 Super 35 Sensor.
And this is how depth of field is affected by sensor size if only indirectly. To get the same shot, a smaller sensor will require a wider lens, and a wider lens will have a broader depth of field.
28mm Lens @ f4 Full Frame Sensor.
28mm Lens @ f4 Super 34 Sensor.
85mm Lens @ f4 Full Frame Sensor.
50mm Lens @ f4 Super 35 Sensor.
28mm Lens @ f4 Full Frame Sensor.
18mm Lens @ f4 Super 35 Sensor.
The image circle
The image circle of different lenses can also be different sizes based on the sensor size the lens is designed to fill. A full frame lens produces an image circle that is large enough to cover the entire full frame sensor. But an APS-C or micro four thirds lens is only designed to create an image circle large enough to cover those respective sensors. As mentioned above, lenses with the same focal length will produce the same image in their image circle, but if you were to attach an APS-C lens to a full frame camera, it would look like George Lucas started a feathered circle wipe to space on the image (for you non-Star-Wars people out there, imagine a very distinct vignette).
Therefore, it is important to choose the right type of lens for your sensor. Yes, you can use a lens that creates a larger image circle than your camera requires (i.e. putting a full frame lens on an APS-C camera), but you might be spending more than necessary. However, there may be a quality difference in the lens that justifies the price difference for your use case.
And that’s why we don’t simply have one standard for lenses. If all lenses were created to cover the largest available sensor, they would work with all the other sensors too. But we would all need to take out a mortgage to afford them plus hire a small army to carry the heavy things around.
Sensitivity
It is tempting to assume that a larger sensor would be more sensitive to light, and all other things being equal, that is likely true. But things are rarely that simple. Sensitivity is really a function of how large the pixels are – or even more accurately, how large the light-sensitive area of each pixel is. So, yes, a larger sensor may mean more sensitivity if that larger sensor is not packed with more pixels (6K, 8K, 12K, etc.). More pixels on the same-sized sensor means smaller pixels, which means less sensitivity. Of course, manufacturers have all kinds of tricks to increase sensitivity these days, so your mileage may vary. It’s always a good idea to research how others rate the low-light capabilities of a camera in real conditions.
If you do a lot of shooting in dark worship environments, you might need both a camera with high sensitivity and a fast lens. To quote the t-shirt of a former coworker, “Without light, it’s just radio.”
Why do I bring up sensitivity during a discussion about lenses? Well, if your camera is more sensitive, perhaps you do not need a faster lens. When talking about lenses, how “fast” the lens is refers to the widest possible aperture. For example, if your camera is more sensitive to light, an f4 lens might be sufficient for your needs as opposed to an f1.2 lens. And a slower lens tends to be more affordable. If you do a lot of shooting in dark worship environments, you might need both a camera with high sensitivity and a fast lens. To quote the t-shirt of a former coworker, “Without light, it’s just radio.”
Final thoughts
There is no blanket answer for the right sensor size and lens combination. The answer will depend on your needs and your budget. Understanding the relationship between sensor size, focal length, and depth of field will help you navigate the decision-making process and choose the best combination for you. The most important thing to remember in the midst of the marketing hype: a larger pixel count (or more K’s) does not mean a larger sensor. Find all of the options that fit your budget and then…choose wisely.
