There are several areas of camera design where decisions drive image quality and cost at the same time. The lens is the first limiting factor. Obviously, just having a bigger lens doesn’t mean that your pictures will be better. The other pieces of the camera also make a difference, but the quality of the glass can make or break your pictures. The physics of light can make it hard to build good small lenses, and mechanical design can make it hard to build a smoothly operating lens of any size. Cameras with built-in lenses can be optimized for a single lens that result in pretty good images, even from a cheaper camera.The second limiter is the image format. More pixels alone don’t make a good picture; too few can introduce artifacts that show up on big images and can leave you with inadequate data to work with later. The same can be said for the number of bits allocated to each pixel for color and brightness information. A great sensor won’t deliver great images through a format bottleneck.
Myth: Only Big, Expensive Cameras Make Good Pictures
Image sensors are getting better and better, but, as in lenses, physics can get in the way. Image size affects the depth of field for a given scene size and limits the sharpness of the image as you stop down (yes, “stop down”) the aperture. A characteristic called “diffraction limiting” restricts the resolving power of any system when the aperture gets small, but you don’t usually see the problem on big lenses and sensors until you’re closed down much more than normal. The size of the sensor also limits light sensitivity because there’s less area to gather light photons, which translates to image information, and this limits the dynamic range for the same reason.
In dramatic shows, apertures tend to be open wide enough to avoid diffraction limiting because cinematographers tend to want shallow depth of field. Sensitivity can be less of an issue because the cameras can be larger and lighting flexible. In sports coverage and other real-time events, shallow depth of field and limited sharpness can make focus difficult, especially at longer focal lengths. Using larger apertures to compensate for lower sensitivity or for diffraction limiting in small-sensor cameras makes focus tracking harder for operators. Problems can also be more visible in documentary, news and sports shooting because multiple takes aren’t an option.
Video Compression & Recording. Optical, sensor and processing electronics designs can make camera matching a big challenge. Luminance transfer characteristics, color gamut and color reproduction (color matrix) control are complicated areas beyond simple color balance and aperture adjustments. Two different cameras with different responses in those areas can deliver reproductions of the same scene that look radically different.
Once you capture decent images, recording or delivery decisions, which move the images to postproduction or live integration with other media, become important to maintaining the quality of the output. Like most elements in the video world, compression has improved considerably. We now have high-quality intraframe compression and improved interframe (or long GOP) coding for a given data rate, but there’s a difference in the cost and space needed for compression electronics and storage between small and large cameras.
Obviously, if you didn’t have to compress the image, you could record the highest quality that the camera can deliver, but there are other reasons why you might not want to. One is the computing power required to manage the high volume of data onto the media, and computing power has battery power implications that can affect camera runtime. Even with enough power, the record media can limit recording time at a given data rate.
There’s also the transfer time to get the data into your postproduction system, the power needed to edit uncompressed streams and the volume of data space needed to store each version of each product delivered. Some of these can be constrained to parts of the workflow, but some will follow you all the way to the archive vault. The introduction of small-format UHD cameras only aggravates the image quality dilemma, but it certainly didn’t introduce these problems. The basic ones were with us in the film days, but few of us knew much about them. Now, we have more words to describe them and we’ve introduced more complexity on the electronic side. We’ve come to expect unprecedented flexibility in our cameras that makes it harder to predict which decisions might be the best for the whole project.
Wrap. So what’s a shooter to do? I know this gets a bit boring, but, as usual, it depends—on how good you are at selecting your tools, crafting your shots and analyzing your images. It depends on how much control you have on the acquisition and postprocessing phases. And, it depends, as always, on how much of several resources you command—money, support people, persuasiveness and tenacity. Sorry, no magic pill.
And, actually, you may get more features in a cheaper camera, depending on which ones you think are important. Some of the features we’ve come to expect in consumer cameras aren’t available or cost a premium in professional models. Autofocus is an example. If you need specific features for a special shot, you may be better off with a cheaper camera, especially since Blackmagic Design joined the fray (but that’s a whole other column).
Charles ‘C.R.’ Caillouet is a technical producer and video engineer who has worked in TV production, from preproduction through field acquisition to postproduction and presentation, as well as for NASA, Sony and Panasonic. He’s currently Technical Director of the Jackson Hole Wildlife Film Festival and Science Media Symposium.