The Digital Sensor: A Guide to Understanding Digital Cameras
by Wesley Fink on April 21, 2008 1:00 AM EST- Posted in
- Digital Camera
Sensors Today
| Sensor Size (mm) | ||
| Type | Width | Height |
| 1/3.6" | 4.00 | 3.00 |
| 1/3.2" | 4.54 | 3.42 |
| 1/3" | 4.80 | 3.60 |
| 1/2.7" | 5.37 | 4.03 |
| 1/2.5" | 5.76 | 4.29 |
| 1/2" | 6.40 | 4.80 |
| 1/1.8" | 7.18 | 5.32 |
| 1/1.7" | 7.60 | 5.70 |
| 2/3" | 8.80 | 6.60 |
| 1" | 12.80 | 9.60 |
| 4/3" | 18.00 | 13.50 |
| APS C | 23.70 | 15.70 |
| 35mm film | 36.00 | 24.00 |
In the above chart, the sensor sizes for today's DSLR cameras are in the range of 4/3" and APS C. A few top pro cameras now sport 35mm-size sensors and are referred to as full frame. Comparing this to Compact or Point and Shoot cameras today we generally find a 1/2.3" to 1/2.5" sensor. A few top-of-the-line compact cameras, like the Canon G9, feature a 1/1.8" to 1/1.7" sensor. To see the difference in the relative size of P&S sensors and DSLR sensors, look at the graphic below.
The very best compact cameras have sensors around the 1/3" to 1/2" range. The APS C to 4/3 sensors of the bulk of today's digital SLR cameras are huge by comparison. The developing push for full-frame at the top of the current DSLR market is a move to a sensor that is a bit more than double the size of today's APS C sensors. The approximate 24mm by 16mm APS C is the same size as the 1/2 frame 35mm championed by Olympus in the film era.
This size actually harkens back to 35mm motion picture film that became the standard on which most of the SLR lens systems are based. 35mm motion picture film contained images of around 24x16mm, and 35mm still film just turned the spool direction and used double the frame size. In fact, some early 35mm still cameras were referred to as "double-frame" cameras.
Why Does Sensor Size Matter?
In some of life's arenas bigger is better, but in computers and electronics we almost always see a trend toward smaller and smaller traces producing chips with higher and higher densities. So the question becomes why is a 10MP DSLR sensor any better than a 10MP Compact or Point and Shoot sensor?
The simple answer is that computer chips are digital devices, made up of transistors that register on and off (1 and 0) states, which are then combined to create the information we crunch in a computer. Digital sensors, on the other hand, are analog devices used to gather light and color information. Every digital camera then has some means to convert this analog sensor data to digital information in its processing path. Devices that communicate on and off do not require the sensitivity of devices that gather and convey more complex data like a digital sensor pixel.
Unlike digital data, all pixels are not created equal. Larger sensors, such as those used in digital SLR cameras, have larger pixels. All things being equal the larger pixels have more light-gathering ability over a given unit of time. This translates into two very important considerations for photography.
First, larger pixels exhibit lower noise than smaller pixels under the same conditions. This improved signal-to-noise ratio means that your 10MP DSLR image will likely produce better, sharper, clearer prints than the smaller 10MP compact (point and shoot) cameras. This improved SNR also means larger sensors produce a wider dynamic range (a greater range between the lightest and darkest elements of the photo).
The second aspect also relates to light gathering ability. Large DSLR sensors have more ability to gather light, which means they generally are more effective over a much wider range of lighting conditions than a compact camera. Many compact cameras are perfectly acceptable at ISO 100 but are very noisy by ISO 400. Most DSLR cameras with their larger sensors produce very acceptable results to ISO 800 or 1600 - ISO options not even available on most compact cameras. Some newer DSLR cameras even offer options of ISO 3200, ISO 6400, or even higher.
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Midwayman - Friday, April 25, 2008 - link
I'm happy. I'll won't argue that it's not a variant, but its design is different enough to warrant a mention. Even for such an old sensor, it still produces a dynamic range that exceeds notables such as the 5d, etc. I know I love my Super CCD based f30.http://www.imaging-resource.com/PRODS/S3/S3PA6.HTM">http://www.imaging-resource.com/PRODS/S3/S3PA6.HTM
Has a reasonably good discussion on the super ccd for those interested.
haplo602 - Thursday, April 24, 2008 - link
http://www.fujifilm.com/products/digital_cameras/s...">http://www.fujifilm.com/products/digital_cameras/s...ElFenix - Wednesday, April 23, 2008 - link
http://gizmodo.com/383170/giz-explains-digital-cam...">http://gizmodo.com/383170/giz-explains-digital-cam...Ajax9000 - Monday, April 21, 2008 - link
Two criticisms of the article.1> The sensor size discussion was rather muddled, with half of the information on p.4 duplicating the info on p.2
2> Yes, full-frame is really nice to aspire to, but the problem of full-frame sensor cost was not mentioned. IC lithographic machines ("steppers") cannot image a FF sensor in a single pass, making the production time cost 2-3x greater than smaller sensors (APS-H is the biggest that can be done as single pass). Worse, the large size of the sensor compared to the wafer means that yields drop appreciably as the sensor size increases. All in all, FF sensors can be 10-20x more expensive than APS-C sensors, let alone 4/3, 1/1.8", etc.
See for example: p.68 in http://www.canon.com/technology/pdf/tech2008e.pdf">http://www.canon.com/technology/pdf/tech2008e.pdf and pp.11&12 in http://www.robgalbraith.com/public_files/Canon_Ful...">http://www.robgalbraith.com/public_files/Canon_Ful...
To quote Canon (2nd ref): "Regardless of future technological developments, cameras with full-frame sensors will always cost much more than cameras with smaller sensors."
ElFenix - Wednesday, April 23, 2008 - link
steppers used to not be able to make 35 mm sensors in one pass. as canon and nikon are two of the bigger stepper manufacturers, guess what has likely happened? and both of them are smart enough to not announce that they've made the larger stepper, so as to make more profit than the other.Wesley Fink - Tuesday, April 22, 2008 - link
Page 2 emphasized the huge size difference between compact point-and-shoot-sensors and DSLR sensors as classes of sensors. Page 3 then explored how all the DSLR sensor sizes evolved within that class, and page 4 detailed the current variations in sensor size within the DSLR class. I appreciate your comments, but can you provide some specifics on what needs to be changed?The full-frame sensor does indeed cost more, which was mentioned a number of times in the article. However, prices are still dropping for the full-frame sensor as evidenced by the fact that the street price of the Canon 5D is now around $2000.
Ajax9000 - Wednesday, April 23, 2008 - link
Some suggested edits:Page 1
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Page 2
Sensors Today
Table: Sensor Comparison
Type Width (mm) Height (mm) Area (mm^2) Percent Full Frame Crop Factor (Lens Multiplier)
1/3.6" 4 3 12.00 1.39 8.49
1/3.2" 4.54 3.42 15.53 1.80 7.46
1/3" 4.8 3.6 17.28 2.00 7.07
1/2.7" 5.37 4.03 21.64 2.50 6.32
1/2.5" 5.76 4.29 24.71 2.86 5.91
1/2" 6.4 4.8 30.72 3.56 5.30
1/1.8" 7.18 5.32 38.20 4.42 4.76
1/1.7" 7.6 5.7 43.32 5.01 4.47
2/3" 8.8 6.6 58.08 6.72 3.86
1" 12.8 9.6 122.88 14.22 2.65
4/3" 18 13.5 243.00 28.13 1.89
"APS C" 23.7 15.7 372.09 43.07 1.52
APS C 25.1 16.7 419.17 48.52 1.44
APS H 30.2 16.7 504.34 58.37 1.31
35mm film 36 24 864 100 1.00
In the above Table we can see the range of sensor sizes now available. However, the majority of Compact or Point and Shoot cameras today still generally use a 1/2.3" to 1/2.5" sensor. A few top-of-the-line compact cameras, like the Canon G9, feature a 1/1.8" to 1/1.7" sensor; and the very best compact cameras have sensors around the 1/3" to 1/2" range. In contrast, the sensor sizes for today's DSLR cameras are in the range of 4/3" and APS C. A few top pro cameras now sport 35mm-size sensors and are referred to as full frame.
The APS C to 4/3 sensors of the bulk of today's digital SLR cameras are huge by comparison to those found in mainstream Compact or Point and Shoot cameras. To see the difference in the relative size of P&S sensors and DSLR sensors, look at the graphic below.
http://images.anandtech.com/reviews/cameras/2008/s...">http://images.anandtech.com/reviews/cameras/2008/s...
[Delete http://images.anandtech.com/reviews/cameras/2008/s...">http://images.anandtech.com/reviews/cameras/2008/s... ]
Why Does Sensor Size Matter?
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Page 3
Why All these Different Sensor Sizes?
35mm first appeared on the scene in the 1930s, using an image frame of around 24x16mm. 35mm still film simply took 35mm motion picture film and spooled it into a light-tight canister, turned the spool direction by 90 degrees, and used double the frame size. (In fact, some early 35mm still cameras were referred to as "double-frame" cameras.) By the 1960s, with point-and-shoot and developments in SLR technology, 35mm had become king of the film formats. Even as film manufacturers tried to introduce other film formats, 35mm continued to grow and prosper.
...
... Actually, the image size that was always shot was the 30.2mm x 16.7mm, and the other sizes were just standard crops. The 24mm by 16mm APS C format is approximately the same size as the 1/2 frame 35mm championed by Olympus in the film era.
Page 4
Sensor Size and Multipliers
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More recently, Canon has championed the full-frame sensor in their pro cameras and in their pro/amateur 5D model. Larger sensor manufacturing cost has dropped as digital sensors have evolved and it now appears likely the APS-H (1.3X lens multiplier) will eventually drop from the Canon line. Since no lenses depend on that image circle all current Canon full-frame lenses, such as those used with the APS-H cameras, will remain usable on the full-frame sensor pro models that will replace them.
The developing push for full-frame at the top of the current DSLR market is a move to a sensor that is a bit more than double the size of today's APS C sensors. And there is a significant problem with this -- the full-frame sensors are made using different process techniques to even APS H sized sensors, greatly increasing their relative costs. In short, the IC lithographic machines ("steppers") that make the sensors cannot image a full frame sensor in a single pass, making the production time cost 2-3x greater than smaller sensors (APS-H is the biggest that can be done as single pass). Worse, the large size of the sensor compared to the wafer means that yields drop appreciably as the sensor size increases. According to Canon USA, full frame sensors can be 10-20x more expensive than APS-C sensors.
(
As a comparison to computer components, most CPUs are less than 300mm^2. The very large and expensive G80 and R600 GPUs are about 480mm^2 and 420mm^2 respectively. Unlike CPUs and GPUs that can increase performance through a die-shrink, APS, 4/3, and full frame sensors have a fixed die size -- so Moores Law doesn't apply.
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It is not surprising then that dSLRs mostly use APS C and 4/3 sensors.
Nikon, Pentax, and Minolta all had significant success in the 35mm film market, so all three had a vested interest in preserving their 35mm lens mount and keeping their current 35mm system users happy. However, none of these three had the resources to develop and manufacture their own sensors, so they partnered with sensor manufacturers to produce digital SLR cameras. Of course, these manufacturers were mostly making APS C, 4/3, and smaller sensors. In recent years that partner has been Sony, so all three manufacturers have basically adopted a 23.6x15.7mm sensor with a 1.5X lens multiplier.
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CSMR - Monday, April 21, 2008 - link
I am not an expert but it seems to me the most important point has been missed in this article: depth of field. Larger sensors allow for greater depth of field with the same lens. There is a lot of discussion of "image quality" (resolution, shutter speed, sensitivity) but depth of field alters what the image is, which is more important.Wesley Fink - Monday, April 21, 2008 - link
In the interest of keeping the article somewhat basic and a digestible size we did not include a discussion of the depth of field variations with compact sensors compared to DSLR sensors.This IS an important concern for creative use of depth of field since the DOF is much greater with the smaller sensor than with the DSLR sensor. Not everyone would agree that a shallower depth of field on a DSLR is more desirable. It certainly might be in a portrait, but not in a sweeping landscape shot. The desired DOF depends on what you are shooting.
melgross - Tuesday, April 22, 2008 - link
This is a very complex subject for many people. It's not just the sensor size that determines depth of field.But, we also have perspective to worry about.