Need help in calculating digital camera's MP

On Sun, 11 Jan 2009 07:45:48 -0800 (PST), Scott W
wrote in
:

On Jan 10, 10:07*am, John Navas wrote:
On Sat, 10 Jan 2009 10:07:18 -0000, "Trev" trevbowdenAT.dsl.pipex.COM
wrote in :

,
John Navas bashed on *keyboard and typed:
Simplified math:

The Canon sensor has a resolution of 5,616 x 3,744 pixels
on a sensor size of 36 x 24 mm.
That's 156 pixels/mm, which needs minimum resolving power of 78 li/mm.
There are very few lenses with that kind of resolving power.
Good zoom lenses are on the order of 40 li/mm.
More resolving power (contrast) is needed for pixel-level crispness.

Ah but the lens can resolve the 40 lpm ( x2 = 80 a sq millimeter) on to one
sq pixel

Nope. *Doesn't work that way. *
Read the citation from my post that you snipped: *
http://www.luminous-landscape.com/tutorials/resolution.shtml

So there table is saying that you would need 29MP for a FF sensor
using a diffraction limited lens at F/8. lens at F/8. And this
ignores much of the issues with bayer sensors so the real number would
have to be higher yet, see note [10] at the bottom of the article.

You seem to have a serious selective perception problem.

--
Best regards,
John
Panasonic DMC-FZ8, DMC-FZ20, and several others

On Sat, 10 Jan 2009 22:37:49 -0000, "Roger Blackwell"
wrote in
:

"John Navas" wrote in message
.. .

Simplified math:

The Canon sensor has a resolution of 5,616 x 3,744 pixels
on a sensor size of 36 x 24 mm.
That's 156 pixels/mm, which needs minimum resolving power of 78 li/mm.
There are very few lenses with that kind of resolving power.
Good zoom lenses are on the order of 40 li/mm.
More resolving power (contrast) is needed for pixel-level crispness.

More complete math:

http://www.luminous-landscape.com/tutorials/resolution.shtml

Consider a 35mm system with a lens at f/11. At best, the maximum
resolution you will get is equivalent to 16 MP, even if your camera
has 22 or 25 MP. In the case of an APS-C based system the limit goes
to 7 MP, and 4 MP considering a Four Thirds format. Stopping down to
f/22 the limit of the effective resolution of the 35mm based system
goes to 4 MP!

Only for highly corrected lenses (with better performance at f/5.6
than f/8) do higher sensor resolutions make sense. For instance, you
can put 60 million of pixels into a 35mm sensor, but only a
diffraction-limited lens at f/5.6 would take advantage of it.

Sensors for larger formats are approaching the diffraction limit of
real lenses, and it is more difficult to get high levels of
aberration suppression for them. THE POINT IS THAT YOU CANNOT FULLY
EXPLOIT THE RESOLUTION POTENTIAL OF HIGH-RESOLUTION SENSORS WITH
REGULAR MASS-PRODUCED LENSES, PARTICULARLY FOR LARGER FORMATS.
[emphasis added]

Well, having said all that a 60" x 40" print from a dSLR will still be
acceptable (at least to my personal standards) if it is interpolated to 300
dpi and the sharpness is the best that can be obtained. After all, who goes
to art galleries with a magnifying glass looking to see the most detail in
the paintwork?

The maximum viewing distance for a given sharpness can be easily
calculated, and it's much farther away than a magnifying glass unless
you assume ideal conditions and/or a large circle of confusion.

--
Best regards,
John
Panasonic DMC-FZ8, DMC-FZ20, and several others