The Digital Sensor: A Guide to Understanding Digital Cameras
by Wesley Fink on April 21, 2008 1:00 AM EST- Posted in
- Digital Camera
Lens Equivalence
It is important to understand that a 50mm lens is always a 50mm lens, as that is the focal length. That 50mm specification affects depth-of-field and other image characteristics tied to the lens focal length. However, we can calculate focal lengths for each multiplier that will give the same field of view in the finished image.
With a closer look at field of view and the impact of the changes in field of view, it is easier to understand recent DSLR lens developments. Early DSLR lenses were generally 35mm lenses mounted on the new smaller sensor cameras, except for complete new systems such as the 4/3 digital-only system championed by Olympus.
Using 35mm or full frame lenses was great if your primary interest was telephoto and bird photography, as that 35mm 70-300mm lens that was the second lens for most film buyers now had a field of view like a 112mm-480mm zoom on the new Canon Digital Rebel. Unfortunately interiors, architectural photography, scenes, and fans of the extreme wide angle point of view were left in the cold in the early transition to small digital sensors.
That has been corrected in recent years with lenses designed for smaller sensors, lenses like the Canon 10-22mm, the Nikon 12-24mm, and similar APS C zooms from Sigma, Tamron, and Tokina. Today, whatever your mount and lens multiplier, there are lens choices that can cover the full range of choices for field of view.
A few lenses by Sigma are actually available in every mount and multiplier listed above. Obviously, these few lenses were originally full-frame 35mm that have been carried over with new coatings for improved performance and reduced flare on digital sensor SLRs. One such lens is the Sigma 24mm f1.8. The field of view on the different mounts and sensors this lens will fit illustrates just how the digital sensor size can influence the use of any lens. On the full-frame Canon5D, IDs III, and Nikon D3 this lens is a fast super wide 24mm. On the Canon 1.3X pro models it is still a fast f1.8, but with the FOV of a 31mm moderate wide angle.
On the Nikon D300/D60, the Sony A700/A350, and the Pentax K20D/K200D this fast lens is now a moderate wide angle to near normal lens that shoots images with a 36mm angle of view. On the Canon XSi and 40D we are at 38mm, which most would consider near normal. The Sigma SD14 FOV of 41mm has definitely crept into the normal range. Finally the 4/3 mount version of this lens is one of the "normal" lens choices on the Olympus E3/E510/E410 and Panasonic and Leica 4/3 digital SLR cameras. The 24mm on a 4/3 camera looks at the world as though it is a 48mm f1.8 lens, and competes with the Leica 25mm f1.4 as a much lower cost normal lens.
Similar comparisons could be made in other focal length ranges, but you get the point. Olympus makes a 70-300mm telephoto lens for 4/3, and it is much sought after by "birders", because the view on a 4/3 camera with this lens extends from 140mm to 600mm.
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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.
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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.
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... 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.
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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.