For a couple of decades now, a cacophony of myth and misinformation has stemmed from digital photography regarding sensor size. This all started because professional and advanced amateur digital photography was rooted, for economic reasons, in 35mm film photography.
Driven mostly by the engines of sales and popularity, not necessity or creativity or technical superiority, the 35mm film frame, at 36x24mm, and originally derived from an industrious camera maker wanting to take advantage of surplus film from the burgeoning 1930s motion picture industry, became the standard bearer for image size by the end of the 20th century.
I recently decided to do a little used-for-used sell-and-buy on Ebay to get my hands on a Nikon D700, one of Nikon’s earliest digital cameras equipped with a sensor the size of a 35mm film frame, 36x24mm, sometimes referred to by the misleading name “full frame” because it is the same size as a full frame of film. Nikon calls it “FX,” in contrast to their smaller 24x15mm sensors, which it calls “DX.” 24x15mm sensors are often mistakenly called “cropped” sensors by laymen who don’t fully understand the origins of image size. If it has to have a name, it is most accurately described by its size in millimeters or by the film size closest to it, APS-C (Advanced Photo System type-C).
The lazy-writing web world often calls full frame “FF” in forum posts.
- Do full frame sensors have “better depth of field”? No. I was eager to debunk this one because I already knew the answer, and because it is an embarrassment to photography that everyone is so eager to believe this. Depth of field is controlled by two factors: magnification and aperture. The reason this myth seems to be true is that to get the same composition on a 36x24mm as on a smaller sensor, one has to either get closer or use a longer focal length, both of which increase magnification to create shallower depth of field. At identical distances, focal lengths and apertures, depth of field is identical. If you don’t believe me, here is the proof…
- Is an aperture of f/2 on a larger sensor “equivalent” in light gathering capacity to f/1.4 on a smaller sensor? No. I heard this one asserted by Tony and Chelsea Northrup on their YouTube channel, and I couldn’t believe my ears at the time. (They also refer to “ISO” as a name – “Eyesoh,” which it is not). I have no idea how they came to this conclusion, but this and the popularity of their channel has done nothing but muddy the waters on issues like this. Simply put, f number is a fraction describing the ratio between the focal length of a lens and the diameter of the opening. A 50mm f/2, for example, has an opening of 25mm. 50 divided by 2 equals 25. A specific aperture value lets the same amount of light through the lens regardless of what size of film or sensor is on the other side.
- Will a larger sensor give life back to my wide angle lenses? Yes, with some caveats. A 20mm lens that was a mediocre lens on a smaller sensor has now been restored to its film-days glory as an ultra wide lens. While this is certainly nice if you have a bunch of old wide angle lenses, today many manufacturers make very wide angle lenses for smaller sensors. I have several myself, and I am able to get as wide as I need, including ultra-ultra-wide using my 10-17mm fisheye and uncurving it in Photoshop.
- Will my telephoto lenses will be less telephoto-y on a larger sensor? Yes. This is the reason sports and wildlife photographers got away from large and medium format film as soon as 35mm was available: just as larger sensors make wide angles wider, they make telephotos wider, since they are projecting their images onto a larger surface. Many top sports and bird photographers very much prefer 24x15mm sensors for just this reason, and this has been a leading marketing tag for Nikon’s flagship 24x15mm camera, the D500.
- Are larger sensors better at capturing low-light scenes due to the pixels themselves being larger? Yes. If you compare a 36x24mm sensor against a 24x15mm sensor of the same pixel count, assuming the sensors are of the same era and treated with the same renderings, noise will be lower in the larger sensor. This is true because the pixels themselves, the tiny light-sensing devices inside the integrated circuit in the middle of the camera, are larger, and can gather more light, thus requiring less amplification of the signals they produce. In practice, though, this rule doesn’t hold much water. There are many smaller-sensor cameras that make incredibly low-noise images, and most cameras with larger than “full frame” sensors do not.
The craving for lower noise at higher ISOs is a symptom of photographers being too lazy to master what matters most, light. Additionally, there is a lot of pretense on the photo forums (like photo.net, which recently changed formats and is now unviewable) about, “wanting to do more street photography.” The truth is that most of time people who make this claim just want to be able to say, “I have this camera and that lens,” and don’t make very many photos. All you have to do to discover this truth is walk the streets and count the photographers: ≈ 0.
- Are “multiplier” or “crop factor” numbers useful? No. These numbers are all over the place, and only exist so camera makers can muddy the waters of what you should buy. 1.5x “crop factor” or 2x “multiplier” is only helpful if you go from one format to the other constantly while shooting. A far better way to understand this is to know your camera, and know what does what. For example, suppose your camera is a “four thirds” format (18x13mm). A 14mm is a wide angle lens, and a 200mm is a super-telephoto.
- Is it worth it to “upgrade” to a larger sensor? No. Anyone who asks this question isn’t ready to take advantage of the subtle differences offered by a larger sensor, and larger sensors are disproportionally more expensive. If you need a larger sensor, you already know it.