The Compact Camera Quandary
– State of the Market, Mid-2007
Page 1, version 1.0, © (Aug.) 2007 by Dale Cotton, all rights reserved
This article is targeted at experienced/advanced photographers and contains time-sensitive material. Best read before end of 2007.
One of the most common topics on photography forums is what compact camera to buy for the advanced photographer to carry and use when a dSLR is too big, too heavy, or too intrusive.
Fig. 1: Compact cameras on store shelves
In general, small cameras are admirably suited to the needs of their typical user, who has little knowledge of photography and who delighted in the 4x6" lab prints s/he used to get from a roll of 35mm in all their high-contrast, blown-highlight, and off-colour glory.
Since there are a million such potential purchasers for every one of us more serious types, it's understandable that the image quality of small cameras is as mediocre as it is. In fact, it's actually getting worse, not better, as manufacturers continue to use extremely small imagers and to divide their extremely small surface area into ever more microscopic pixels.
The decline and fall of the compact camera
Fig. 2: Sensor size comparison
Fig. 2 shows two of the most common compact camera sensor sizes – obscurely named 1/2.5" and 1/1.8" – compared to one of the standard dSLR sizes and 35mm film. The 35mm rectangle is also the same size as the expensive full frame dSLR sensor size and is 1" by 1.5" (24 by 36 mm) to give a sense of scale. Learn more at dpreview.com.
The blow-up schematic of a corner of the tiny 1/2.5" sensor shows how its already minute surface area is further divided into individual pixels (white boxes); and only some fraction of each pixel's surface area actually collects light (black boxes). Pixel dimensions are measured in microns (millionths of an inch). The more pixels you cram on to a given sensor size like 1/2.5" the smaller each pixel is and therefore – barring improvements in light collection efficiency – the less light each pixel can gather. Such improvements have been much slower in coming than the increase in pixel counts they offset.
Pixel counts have moved from 7 mp, to 8, to 10, in the past two years, and now 12 mp small cameras are starting to appear right on schedule ... but with no change to the overall imager dimensions. This results in more intrinsic noise per ISO level and less exposure latitude (dynamic range).
Fig. 3: Book spines. 1/1.8" CCD noise (Coolpix 7600) at 200 ISO
The random-coloured speckling of noise in Fig. 3 isn't pronounced in the light-coloured book spine to the left but obscures all detail in the dark shadows near the centre of the image.
To understand why this is so, consider the following tables, which show the pixel size in microns (millionths of an inch) for various sensors, based on my calculations (divide sensor height in mm by image height in pixels). The pixel sizes also act as approximate signal-to-noise (s/n) ratios, if we assume the same or equivalent sensor technology (quantum efficiency) in each case. Thus, a typical 10mp 1/1.8" compact camera sensor would have 1/3 the s/n ratio, or 3 times the noise, of a typical 10mp APS-C sensor, if both were cut from the same silicon wafer:
| dSLR sensors |
2/3" sensors |
1/1.8" sensors |
1/2.5" sensors |
| sensor size |
mega- pixels |
pixel size |
| FF/35mm |
12.8 |
8.4 |
| APS-C |
6 |
7.8 |
| FF/35mm |
16.6 |
7.2 |
| 4/3 |
5 |
6.8 |
| APS-C |
10 |
6.0 |
| 4/3 |
10 |
4.9 |
|
| sensor size |
mega- pixels |
pixel size |
| 2/3" |
1.3 |
6.4 |
| 2/3" |
2 |
5.5 |
| 2/3" |
3 |
4.3 |
| 2/3" |
6 |
3.3 |
| 2/3" |
10 |
2.4 |
| 2/3" |
12 |
2.2 |
|
| sensor size |
mega- pixels |
pixel size |
| 1/1.8" |
1.3 |
5.2 |
| 1/1.8" |
2 |
4.4 |
| 1/1.8" |
3 |
3.5 |
| 1/1.8" |
6 |
2.7 |
| 1/1.8" |
10 |
1.9 |
| 1/1.8" |
12 |
1.8 |
|
| sensor size |
mega- pixels |
pixel size |
| 1/2.5" |
1.3 |
4.2 |
| 1/2.5" |
2 |
3.6 |
| 1/2.5" |
3 |
2.8 |
| 1/2.5" |
6 |
2.1 |
| 1/2.5" |
10 |
1.6 |
| 1/2.5" |
12 |
1.4 |
|
Thus, for a manufacturer to give us anything close to the s/n of a typical 10 mp dSLR in a compact it would have to use somewhere around a 1 or 2 megapixel 2/3" sensor. A 6 mp 2/3" sensor would cut the s/n down to about half that, thereby doubling the noise.
The greater pixel counts might be at least partially excusable if there were a corresponding increase in resolution, but in some cases there has been no such increase (presumably having reached the limits of the optics), while in others the increase has not been proportional to to the increase in pixels.
In short: the glut of compact cameras models on store shelves represents a vast desert of mediocre-to-poor image quality and poor-to-abysmal handling. There is some good news: the unusable shutter lags of years gone by have largely been replaced by something that verges on the acceptable – although anything resembling dSLR frames per second rates remains a pipe dream.
Let's take a quick tour of the important features of digital cameras. To keep things manageable we'll make certain assumptions – that you
- will mostly be using the camera handheld
- will prefer more wide angle to longer telephoto
- will prefer existing light to flash
- will use it at least as often in low light as in bright
- will use it for active, as well as static, subject matter.
Page 2: Handling issues.
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