Certainly, a hackneyed, old phrase, but in matters of digital photography, it is a fact. The size I am referring to is the digital sensor, but not megapixels; physical size. There are a fair number of parallels to the film-based systems we used before the so-called, “digital revolution.” But with digital sensors, there is a significant difference; technology. Very much like the computer industry, by the time the latest and greatest sensor hits the market, it is already “old technology” (there were major technological advances in film, too, over time, but they happened in a matter of years, rather than months). This is a very technical subject that many others out on the net explain in technical and engineering details that I cannot begin to match. This is a layman’s perspective.
The consumer camera began to drive new technology advances
The first digital cameras were adaptations of 35mm Single Lens Reflex (SLR) camera bodies that were used to build digital imaging tools (today referred to as a Digital SLR; or DSLR). They had very small imaging sensors (significantly, smaller than the rectangular cross-section of a single 35mm film frame), and were capable of producing only around 1.2 megapixel (MP) images. They cost $20,000 to $25,000; not within the budget of most photo-enthusiasts.
Digital image-making brought a new phenomenon to the camera manufacturing industry. Suddenly, the consumer camera (we often refer to them as “point and shoot” or “P&S”), began to drive new technology advances which often first appeared in the consumer P&S cameras, only to be put into the higher-end “pro” cameras later.
How does this all relate to sensor size? The P&S cameras have a much smaller image sensor in them than the DSLR cameras and the newer Medium Format digital cameras that are now available on the market. I currently routinely carry and use 3 different cameras: a Canon G12 P&S, a Nikon D7000 “DX” sensor camera, and a Nikon D700 “FX” sensor camera. As the illustration shows, there is a pretty remarkable difference in sensor sizes (if you would like to do your own comparison, I used this really cool tool to make this illustration). Especially when we can upload and view all three of these at relatively the same viewing size on our computer monitors, and—within reason—make similar-sized print images from all three. But there is a notable difference in the quality of these images.
Why did the original cameras not have a sensor identical to the 35mm film cross-section that those bodies were designed for? The answer is simple; technology and cost. The technology that continues to “knock our socks off” today was the most limiting factor back in the late 1980′s. The cost to manufacture even a 1.2 megapixel small physical sensor was prohibitive. A 35mm size sensor cost as much as 20 times the cost to manufacture the smaller sensors. And while over time manufacturers rapidly designed and manufactured sensors holding many more photo-sites (hence, more megapixel capture capability), the cost to manufacture larger physical sensors remained expensive. This explains why the cost of the so-called “full-frame” DSLR is still substantially higher that a higher megapixel DSLR with the smaller sensor.
Why weren’t the original sensors identical to the 35mm frame size?
Megapixel Wars. For the first 10 to 12 years after the introduction of the consumer-affordable DSLRs, there was a huge emphasis—and indeed a “race”—for more and more megapixels. Megapixels translated in many people’s minds into higher quality. There is some truth to this, but it is only part of the story. When I talk about “size” here, I really mean the physical size of the sensor, more than the number of megapixels. As Thom Hogan recently noted in his D800 review, the megapixel increases are linear, not geometric. In other words, the 36 megapixel sensor in the D800 does not create images 3 times larger than the D700′s 12 megapixel sensor (in fact, Hogan estimates that the increase from the D700 to the D800′s image sizes are about 70%). The arguably more important part of the story is the quality of those megapixels.
My first DSLR was the Nikon D100; a 6 megapixel camera. My “upgrade” to the D200 was 10 megapixels. My current “pro” model D700 is a 12 megapixel camera; while my “backup” D7000 is a 16 megapixel camera. Logically, it would seem that the progression from D100 to D7000 kept getting me to the best sensor. But that is not the case. The older, 12 Megapixel D700 sensor still yields a much higher “quality” image than the 16 Megapixel D7000 sensor.
You might think that the progression from D100 to D7000 kept getting me to the best sensor. But that is not the case
At the time I bought the D100, there were point and shoot cameras available with higher than 6 megapixel counts. But I could still produce a cleaner, better quality image with the D100 that could be printed larger (I have 13 x 19 prints of images made on the D100 that are indistinguishable at that size from prints made from D700 12 megapixel images). Nikon’s newest “entry-model” consumer DSLR is the D3200, which is a whopping 24 megapixels (only the pro D800 beats it with 36 megapixels – the largest megapixel DLSR available at this writing). One would think it should make “better” images than the only 12 megapixel D700. But it cannot even come close!
The primary reason for this is size. You can readily see the difference in the image sensor sizes of my 3 current cameras. And the number of photo-sites that are packed onto the sensor and the size of the photo-sites make a huge difference in the quality of the image produced. This is most obvious in the low frequency (shadows and low light) side of the digital photographic equation.
Noise. When a sensor captures light it is converting light to electrical signals and certain “stray” signals can produce a grain-like pattern or effect in an image that is referred to as noise. This noise is largely created by low frequency signals (often the product of low-light conditions), but also by heat and other anomalies in the electronic processor. A small sensor, with many photo-sites packed onto it can create more degrading noise than a larger sensor. It can generate and accumulate more heat because it has less area to dissipate the heat energy. At the same time, the larger photo-sites are capable of capturing more and better detail, yielding a better quality digital image. These higher quality “raw” images, in turn, yield much better files to work with in the post processing stages. The image here, taken at the Princess Cruise Terminal in Ft. Lauderdale, Florida, in the early morning hours, demonstrates this. The noise is simply un-manageable. The same shot, taken with the D700 would have been salvageable.
Angle of View. Another controversial area over the years has been the concept often referred to as “crop factor,” or “magnification factor.” When manufacturers began making digital interchangeable-lens camera bodies, they simply adapted the current, 35mm SLR body. While one might wonder why they didn’t just design and build a new “digital” body, the most obvious answer is probably again based on economics. It was probably much less costly to adapt the 35mm SLR body. And, it meant not having to create a completely new lens mount and require all of us to buy a whole new series of lenses. They had a ready-made consumer, just waiting to purchase the DSLR and use their existing lenses. The composite above is shots from the same tripod position, taken a 140 mm on all three cameras, at their maximum aperture. The G12 is obviously with its built-in lens. The Nikon is with a 70-200mm f2.8 zoom.
The “crop factor” / “magnification” debate doesn’t really matter
The first sensors were significantly smaller in cross section than the 35mm film frame. The SLR lenses were designed for the larger 35mm cross-section. So, the sensors only used some of the inner part of the lens circle, effectively “cropping” the outer part. The effect of this was to create a narrower angle of view. The appearance is a “telephoto effect.” The practical effect was that you lost your wider angle and “gained” a longer view on all of your lenses, by a factor of 1.3 or 1.5. Because these sensors were similar to the size of the (largely failed) Nikon Pronea APS film camera, they came to be known as “APS” size sensors (Nikon has since denominated their “APS” sized sensor as a “DX” sensor).
There is no such thing as a “full frame” camera
There has been a considerable amount of debate and even “flame wars” on the internet over this concept. It really doesn’t matter. The debate is, for practical shooting, silly. The reality is that if you have a wide angle lens, on an APS sensor, it just won’t view or capture as wide. Conversely, if you have a longer lens, you get a longer angle of view on the entire sensor, effectively increasing the “telephoto” effect of the lens. Depending on your intended use, this can be a good thing or a bad thing (I actually made my recent backup decision to buy an APS size sensor partly on the premise that it would give me slightly more length for certain wildlife shooting).
Likewise, the controversy over whether a camera is or is not “full frame” is non-productive. But I’ll weigh in anyway . There is simply no such thing as a “full-frame” camera. I know that might draw some debate, but it is just a reference point. To a lifelong 35mm shooter, “full frame” means 35 mm (24mm x 36mm). But to a Medium Format or View Camera user, that’ hardly “full.” Indeed a View Camera 8 x 12 sheet of film makes a so-called “full frame” 35mm look like what it really is: a Postage Stamp! Again, it’s a reference point. To my way of thinking, the larger the better.
But there are practical considerations. When I bought my 6 megapixel APS frame D100, I carried a couple 2G flash cards around. With my 12 megapixel “full frame” (Nikon refers to their 35mm size frame as “FX”) D700, I use 8G cards. With the new D800 36 megapixel FX sensor, I don’t even know how large the cards would have to be. And with each of these increases in file size, an equal increase in hard drive storage and computer processing power (memory) is needed. At some point, it may become overkill. When Nikon announced their Flagship D4, at “only” 16 megapixels (same as the D7000 consumer body), many of us thought it might signal the end of the megapixel wars). But they have since released the D800 FX 36 megapixel body. Interestingly, the D800 is the “entry-level pro” camera and the D4 is the flagship pro body at a significantly higher price point (suggesting that a lot of working pro’s don’t consider the megapixel issue significant anymore at 16 megapixels). I cannot personally see a need for more than double the capacity of my D700 which creates some splendid digital images, in low light conditions.
It is difficult or impossible to get those pleasing out of focus effects on a point and shoot camera
Depth of Field. Interestingly, sensor size also affects depth of field. This is analogous to the film reference above (as was the comment about “full frame, Medium and Large Format). It relates to the field of view and image size geometry. I am not capable of explaining the science, here and will leave it to more capable persons. But as a general rule, the smaller the sensor, the greater the depth of field for a given lens focal length. This explains why it is difficult or impossible to get those pleasing out of focus effects on a point and shoot camera. As you an see, the G12 image, which is shot at its longest focal length and its widest aperture, still captures the background in reasonably sharp focus. On the D700, everything is blurred except the main subject (of course a big part of that is the wider aperture).
In the end, it is still first and foremost, about quality! When the consumer affordable DSLRs first came on the market, there was an immediate hue and cry for a “full frame” (i.e., 35mm size) sensor. The main reason, I believe, was because those of us used to using 35mm didn’t like the change required when thinking about and using our existing lens arsenals. I bought an 18mm lens and it solved my concern. Over time, the camera lens manufacturers have answered the call by designing lenses specifically for the APS sensor size. This has created some of its own issues, as we now have 35mm size sensors available. A “DX” lens on my “FX” D700 will have a big black vignette circle in the viewfinder, but will simply crop the image to the DX format. It just means we have to plan and think about what and how we are shooting.
My primary criteria for purchasing a camera will always be its sensor quality
When the D700 came out, I immediately decided to buy it. The sensor size really had absolutely nothing to do with it. I had “moved on” to the smaller sensor / lens combinations and had a bag of lenses that worked well for me. Buying the D700 made me have to re-think that and it was, frankly, in the short run, a nuisance to do so. Eventually I have sorted that all out. But my primary criteria for purchasing the D700 – and it will probably always be my primary consideration in purchasing any camera, was sensor image quality. And there is just no question on my mind that the camera I have in the bag that yields the highest quality image, is the one with the biggest sensor.
Filed under: PHOTOGRAPHY, TUTORIALS | Tagged: Andy Richards, angle of view, APS, aspect ratio, Canon, crop factor, digital photography, DSLR, DX, full frame, FX, image quality megapixel, lens, LightCentric Photography, magnification factor, Nikon, PHOTOGRAPHY, pixel, Point and Shoot, sensor, SLR | 11 Comments »