On Fri, 26 Jan 2007 14:34:44 GMT, Paul D. Sullivan wrote:
>> 5 or 6MP would be a better match for the sensor size.
>>
>> David
>
> The Canon A640 does 10mp on its sensor. Is that not a good match
> either?
If 7mp is too many pixels for the SP-550's 1/2.5" sensor, then 10mp
is also too many for the A640's larger 1/1.8" sensor. The A640
doesn't cram the pixels quite as tightly, but it's pretty close,
with less than a 10% difference. If you want to work it out for
yourself, dpreview gives these dimensions for the sensors, including
for comparison APS-C, which is roughly comparable to the size of
most DSLR sensors:
> 1/2.5" == 5.760mm x 4.290mm == 24.71 sq.mm
> 1/1.8" == 7.176mm x 5.319mm == 38.17 sq.mm
> 1.8" (APS-C) == 23.7mm x 15.7mm == 372 sq.mm
Comparing the 10mp A640 with the 7mp A620, the increased number of
pixels doesn't translate to the same increase in resolution. The
horizontal and vertical absolute resolution increased from 1,550 and
1,600 LPH to 1,775 and 1,850 LPH. This is very close to what you'd
expect from an increase of 7mp to 8mp. If the A640's resolution
increased in proportion to its 10 mp, it would have achieved 2,214
(hor) and 2,286 (vert) LPH. Along with its very modest improvement
over the A620, the A640 is probably a bit noisier at the high ISOs.
(see
http://www.dpreview.com/reviews/canona640/page15.asp )
How does my old Fuji S5100 with its small 1/2.5" 4mp compare?
According to dpreview, absolute resolution is 1,200 and 1,250 LPH.
Not too bad, and the diminishing returns gotten from the higher mp
count sensors is apparent. If the S5100's sensor was enlarged in
its physical dimensions to provide an increase from 4mp to 7mp and
10mp (assuming a perfect lens to match), its resolution would
increase to 2,100 and 2,188 LPH (7mp) and 3,000 and 3,125 LPH
(10mp). The A620 (which I also own) and the A640 don't come close
to matching these resolutions. In other words, as most people here
have long recognized, the megapixel race is mainly a numbers game
devised by the camera manufacturers' marketing departments. It
helps sell cameras, but doesn't help make good purchasing decisions.
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