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Megapixels vs Sensor size

 
 
Bob Williams
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      01-25-2006
My very first digital camera purchased in early 2000 was a Canon S20.
Its sensor size was 1/1.8" and it had 3.3 MP
Its sensor Area/MP was 11.6 sq. microns
In late 2005, Canon released the S80.
Its sensor size was also 1/1.8" but it had 8.0 MP
Its sensor Area/MP was 4.8 sq. microns

Comparing image quality in Steve Digican Site, the S80's images, as
expected, are much better. My question is :
What advances in technology allowed Canon to achieve better image
quality with no apparent increase in noise level with a much smaller
sensel size?

Improvement in sensor efficiency?
Better lens design?
Lower Noise Amplifiers?
Better algorithms to process the data?
All of the above?
Any thoughts on the subject? "Inquiring Minds Want To Know" <G>
Bob Williams

 
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David J. Littleboy
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      01-25-2006

"Bob Williams" <(E-Mail Removed)> wrote:
> My very first digital camera purchased in early 2000 was a Canon S20.
> Its sensor size was 1/1.8" and it had 3.3 MP
> Its sensor Area/MP was 11.6 sq. microns
> In late 2005, Canon released the S80.
> Its sensor size was also 1/1.8" but it had 8.0 MP
> Its sensor Area/MP was 4.8 sq. microns
>
> Comparing image quality in Steve Digican Site, the S80's images, as
> expected, are much better. My question is :
> What advances in technology allowed Canon to achieve better image quality
> with no apparent increase in noise level with a much smaller sensel size?
>
> Improvement in sensor efficiency?


Better sensor design. Better microlenses, lower circuit noise.

> Better lens design?


Irrelevant to nois.

> Lower Noise Amplifiers?


Very much so. It's exactly this sort of area that Sony's been busting their
butts. Look through the back issues of Sony's CX-NEWS for articles on
sensors to see what they've been up to over the last five years.

http://www.sony.net/Products/SC-HP/cx_news/

> Better algorithms to process the data?


Somewhat, but the tweaks in the sensors are the most important.

David J. Littleboy
Tokyo, Japan


 
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Bob Williams
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      01-26-2006


David J. Littleboy wrote:
> "Bob Williams" <(E-Mail Removed)> wrote:
>
>>My very first digital camera purchased in early 2000 was a Canon S20.
>>Its sensor size was 1/1.8" and it had 3.3 MP
>>Its sensor Area/MP was 11.6 sq. microns
>>In late 2005, Canon released the S80.
>>Its sensor size was also 1/1.8" but it had 8.0 MP
>>Its sensor Area/MP was 4.8 sq. microns
>>
>>Comparing image quality in Steve Digican Site, the S80's images, as
>>expected, are much better. My question is :
>>What advances in technology allowed Canon to achieve better image quality
>>with no apparent increase in noise level with a much smaller sensel size?
>>
>>Improvement in sensor efficiency?

>
>
> Better sensor design. Better microlenses, lower circuit noise.
>
>
>>Better lens design?

>
>
> Irrelevant to nois.
>
>
>>Lower Noise Amplifiers?

>
>
> Very much so. It's exactly this sort of area that Sony's been busting their
> butts. Look through the back issues of Sony's CX-NEWS for articles on
> sensors to see what they've been up to over the last five years.
>
> http://www.sony.net/Products/SC-HP/cx_news/
>
>
>>Better algorithms to process the data?

>
>
> Somewhat, but the tweaks in the sensors are the most important.
>
> David J. Littleboy
> Tokyo, Japan



Even though lens quality doesn't affect noise, it certainly affects the
sharpness of the image. A sharp lens would allow the smaller sensel to
capture as much or more detail than the larger sensel captured with a
poorer lens.
Bob

 
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frederick
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      01-27-2006
Bob Williams wrote:
>
>
> Even though lens quality doesn't affect noise, it certainly affects the
> sharpness of the image. A sharp lens would allow the smaller sensel to
> capture as much or more detail than the larger sensel captured with a
> poorer lens.
> Bob
>

Making sharp lenses for smaller sensors is much simpler and less
expensive than for lenses as sensor size increases. The entire compact
camera with lens by Zeiss etc, costs a fraction of the price of one
fixed focal length lens for 35mm with the same brand on it.
Forgetting noise performance, and assuming good lens quality then the
largest practical difference between sensor size relates to depth of
field, and the ratio of sensor size, pixel size, pixel count, and
diffraction limitations on resolution.

Some approximate comparisons are that a 1 1/8" sensor at a given focal
length equivalent and focus distance offers a similar depth of field
when the lens is open fully wide - say f2 or so, as a typical dslr
sensor of 6-8mp at the same focal length equivalent set at the smallest
aperture (around f11 or so) above which diffraction effects begin to
limit resolution. But the 8mp compact camera with 1 1/8" sensor will
progressively lose resolution to diffraction at apertures smaller than
about f4 - so there is little scope to use depth of field creatively as
for a larger format camera, as there are only a couple of "usable"
f-stops before resolution is lost to diffraction. Conversely, the dslr
will never be able to provide the huge depth of field of the compact
camera whilst maintaining the resolution obtainable at apertures wider
than the diffraction limit.

The interrelationship between sensor size, pixel count, focal length,
focal length equivalent, depth of field, and diffraction limitation on
resolution is well explained here:
http://www.cambridgeincolour.com/tut...ensor-size.htm

This web site includes several calculators that can be used to make
comparisons between formats. Diffraction effects occur regardless of
lens quality. There are some serious disadvantages to increased sensor
size as well as serious advantages.
 
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