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But they aren't the only two options. With the quality of lens on the average compact camera for instance, I struggle to see any real noticable improvement abo

But they aren't the only two options. With the quality of lens on the average compact camera for instance, I struggle to see any real noticable improvement above around 5 MP.

theatrus2 14y ago
Lenses are very constrained by physics, and cost. Ground glass and more exotic materials are expensive to produce - injection molded plastic isn't. A high MP sensor is miles cheaper than an upgraded optical system.
- vanderZwan 14y ago
  And a cheap lens with low optical resolution makes a higher number of pixels effectively useless, so it's still a strange development.
  - quantumstate 14y ago
    Higher pixel counts give less noise assuming the total light collection area is the same. Normally you get a bit less light collection area due to the gaps between pixels with a higher resolution sensor but overall I think higher pixel count generally wins, especially when working at the low iso end. So as long as the cost is reasonable why not stick lots of pixels in.
    - ScottBurson 14y ago
      No, smaller pixels have more noise (on a pixel basis) because the incoming photons are averaged over a smaller area. Of course, if you have more resolution, you can reduce the resolution in post-processing, and that will also reduce the noise. But then you might as well have used larger pixels to start with. So I think the right strategy is, figure out how much resolution you need and how large a sensor you can afford, and then make the pixels as large as possible at that resolution. This appears to be what Canon has done.
      - Gravityloss 14y ago
        It would make sense to always process the higher resolution image with denoising and demosaicing algorithms and then save that with a much lower resolution as there is less and less information the lower photon counts you use per pixel. Otherwise you're just saving noise. Probably if you did a study from people's online photo albums where they just upload originals without thinking, you'd discover that something like 90% of space is wasted on pure noise. Things like the sky or a smooth constant color area that can not be compressed by the jpg algorithm since it is filled with high frequency noise. (Often of the color variety no less.) There are limits to sensor efficiency. Photon noise statistics gets worse with smaller absolute aperture lenses (focal length times f-number) and smaller field of view (zoom).
klodolph 14y ago
If you're looking for a 20% improvement from 5 MP to 6 MP, you won't find it. It's really more like a 10% improvement. How many MP does a camera have, if it has twice the resolution of a 5 MP camera? It has 20 MP, not 10. There are also physical limits. The angular resolution depends on the lens aperture size. Smaller cameras have smaller lenses with smaller apertures, which must have lower angular resolution just because of the laws of physics. At the same time, engineering trade-offs mean that smaller lenses usually have larger apertures proportional to their focal length, so this difference is not quite proportional. But these small cameras do not have unreasonable resolutions. I just looked up the specs for a tiny point-and-shoot, the Nikon Coolpix AW100. From the specs (5-25mm lens, 28-140mm equivalent) we can figure out that the sensor is probably about 6.2mm across (36mm * 5mm / 28mm). The lens is f/3.9, which gives a resolution of about 400 lp/mm in visible light, or about 5000 pixels across 6.2mm. The sensor is 16 MP with about 4600 pixels across it. So the sensor is close to the limits of the optical system. If you're having trouble noticing improvement above 5 MP, it is probably due to technique rather than equipment. * You need to use a tripod. (Or a flash. This should be apparent.) * You must not open the lens fully, this will blur the image from lens imperfections. (Look at the MTF charts of your favorite lens. They're way worse when the lens is fully open.) * You must not close the lens more than a couple stops, this will blur the image from diffraction of light through the lens aperture. (Rayleigh limit. You can do the math yourself.) * You need to be very careful with focus. (In my experience, the "hyperfocal distance" is total bunk when you're doing critical work, which makes sense because the hyperfocal formula is based on the assumption that diffraction is irrelevant. When you want maximum sharpness, you'll be shooting near the diffraction limit so it will be relevant, and therefore the hyperfocal formula is wrong. If I remember right, the adjusted formula is based on lens travel distance from farthest to closest subject point, but I've been using the same lens for so long I use intuition.)
- prof_hobart 14y ago
  >The lens is f/3.9, which gives a resolution of about 400 lp/mm in visible light Assuming that you've got a perfect lens. As you say yourself "You must not open the lens fully", in which case the f/3.9 is irrelevant. And even stopped-down, the glass (of which there's several elements in the average compact's zoom) is rarely of the highest quality. All of this makes for an effective resolution some way short of the figures you're quoting. The quality of the lens can make a huge difference. On my main DSLR, the difference in quality between, say, the 50mm f1.2L and and an identical shot taken with a bog standard 17-85 f/4, even at the same f-stop is vast. If the cheaper lenses on DLSRs aren't able to really give enough quality to fully take advantage of higher MP, I'm not quite sure why you'd think that the ones on a compact would be.

But they aren't the only two options. With the quality of lens on the average compact camera for instance, I struggle to see any real noticable improvement above around 5 MP.

theatrus2 14y ago

Lenses are very constrained by physics, and cost. Ground glass and more exotic materials are expensive to produce - injection molded plastic isn't. A high MP sensor is miles cheaper than an upgraded optical system.

vanderZwan 14y ago
And a cheap lens with low optical resolution makes a higher number of pixels effectively useless, so it's still a strange development.
- quantumstate 14y ago
  Higher pixel counts give less noise assuming the total light collection area is the same. Normally you get a bit less light collection area due to the gaps between pixels with a higher resolution sensor but overall I think higher pixel count generally wins, especially when working at the low iso end. So as long as the cost is reasonable why not stick lots of pixels in.
  - ScottBurson 14y ago
    No, smaller pixels have more noise (on a pixel basis) because the incoming photons are averaged over a smaller area. Of course, if you have more resolution, you can reduce the resolution in post-processing, and that will also reduce the noise. But then you might as well have used larger pixels to start with. So I think the right strategy is, figure out how much resolution you need and how large a sensor you can afford, and then make the pixels as large as possible at that resolution. This appears to be what Canon has done.
    - Gravityloss 14y ago
      It would make sense to always process the higher resolution image with denoising and demosaicing algorithms and then save that with a much lower resolution as there is less and less information the lower photon counts you use per pixel. Otherwise you're just saving noise. Probably if you did a study from people's online photo albums where they just upload originals without thinking, you'd discover that something like 90% of space is wasted on pure noise. Things like the sky or a smooth constant color area that can not be compressed by the jpg algorithm since it is filled with high frequency noise. (Often of the color variety no less.) There are limits to sensor efficiency. Photon noise statistics gets worse with smaller absolute aperture lenses (focal length times f-number) and smaller field of view (zoom).

klodolph 14y ago

If you're looking for a 20% improvement from 5 MP to 6 MP, you won't find it. It's really more like a 10% improvement. How many MP does a camera have, if it has twice the resolution of a 5 MP camera? It has 20 MP, not 10. There are also physical limits. The angular resolution depends on the lens aperture size. Smaller cameras have smaller lenses with smaller apertures, which must have lower angular resolution just because of the laws of physics. At the same time, engineering trade-offs mean that smaller lenses usually have larger apertures proportional to their focal length, so this difference is not quite proportional. But these small cameras do not have unreasonable resolutions. I just looked up the specs for a tiny point-and-shoot, the Nikon Coolpix AW100. From the specs (5-25mm lens, 28-140mm equivalent) we can figure out that the sensor is probably about 6.2mm across (36mm * 5mm / 28mm). The lens is f/3.9, which gives a resolution of about 400 lp/mm in visible light, or about 5000 pixels across 6.2mm. The sensor is 16 MP with about 4600 pixels across it. So the sensor is close to the limits of the optical system. If you're having trouble noticing improvement above 5 MP, it is probably due to technique rather than equipment. * You need to use a tripod. (Or a flash. This should be apparent.) * You must not open the lens fully, this will blur the image from lens imperfections. (Look at the MTF charts of your favorite lens. They're way worse when the lens is fully open.) * You must not close the lens more than a couple stops, this will blur the image from diffraction of light through the lens aperture. (Rayleigh limit. You can do the math yourself.) * You need to be very careful with focus. (In my experience, the "hyperfocal distance" is total bunk when you're doing critical work, which makes sense because the hyperfocal formula is based on the assumption that diffraction is irrelevant. When you want maximum sharpness, you'll be shooting near the diffraction limit so it will be relevant, and therefore the hyperfocal formula is wrong. If I remember right, the adjusted formula is based on lens travel distance from farthest to closest subject point, but I've been using the same lens for so long I use intuition.)

prof_hobart 14y ago
>The lens is f/3.9, which gives a resolution of about 400 lp/mm in visible light Assuming that you've got a perfect lens. As you say yourself "You must not open the lens fully", in which case the f/3.9 is irrelevant. And even stopped-down, the glass (of which there's several elements in the average compact's zoom) is rarely of the highest quality. All of this makes for an effective resolution some way short of the figures you're quoting. The quality of the lens can make a huge difference. On my main DSLR, the difference in quality between, say, the 50mm f1.2L and and an identical shot taken with a bog standard 17-85 f/4, even at the same f-stop is vast. If the cheaper lenses on DLSRs aren't able to really give enough quality to fully take advantage of higher MP, I'm not quite sure why you'd think that the ones on a compact would be.