Brad Sanborne wrote:
On Thu, 27 Aug 2009 00:40:50 +0200, Wolfgang Weisselberg
Brad Sanborne wrote:
On Sat, 22 Aug 2009 04:44:31 -0500, Brad Sanborne
wrote:

Do the math on how much magnification you are
seeing by viewing a 3648 pixel-width image from a 10-megapixel camera on an
average 96-dpi LCD monitor at 1:1 resolution. That's like looking at a
negative with a 38x-power dissecting microscope.

Correction.

Let's for the sake of argument take a 10-megapixel P&S camera at 3648
pixels wide and a sensor width of 5.75mm. That's 634.5 pixels per mm.
That's 16,116 pixels per inch. On a 96-dpi monitor viewed at 1:1 that's
like looking at a negative with a 168x microscope.

Let's for the sake of the argument not forget that the standard
size one looks at through the loupe is not a 4.31x5.75mm,
but a 24x36mm frame (for common compact P&S cameras), if not
larger (for less P&Ssy cameras). So it's 101.3 pixels per mm
equivalent and thus 2574 pixels per inch equivalent. On a
96-ppi monitor: 27x equivalent.

Or how about a 15.1 megapixel dSLR at 4752 pixels wide and a sensor width
of 22.3mm. That's 213 pixels per mm. That's 5,410 pixels per inch. On a
96-dpi monitor viewed at 1:1 that's like looking at a negative with a 56x
microscope.

Nope: 132 p/mm = 3.353 p/in = 35x --- assuming a 35mm would
have held 15MPix of data and little enough grain for a matching
enlargement.


Now why on earth did you do all that math over when the same calculations
were already done in the last paragraph?

Because your's were wrong.
29x != 27x (actually 26.8111...x) and 36x != 35x (actually 34.952x).

Only you did them in error.

I did? Really?

The width of a 35mm film frame is 36mm.

That must be the reason why I wrote "24x36mm frame".
That must be the reason why I calculated
3648 p / 36 mm ~= 101.3 p/mm
^^^^^
4752 p / 36 mm = 132 p/mm
.. ^^^^^

Oh, did you think "assuming a 35mm [negative] would have held
15MPix of data [...]" had to be "assuming a 35mm [width] would
have held 15MPix [...]".
Why on earth would one think a one-dimensional *length* could
hold 15MPix?
Why on earth didn't even check the math?
How on earth did you come up with the wrong answers --- and
differently wrong answers for each calculation?

Do you always like making a fool of yourself so publicly?

Yes, I love doing that, especially as it turns out you're
wrong and I am right.

Maybe you just have an OCD involving mathematical masturbation.

Maybe you just don't grasp math.

On Sat, 22 Aug 2009 05:13:32 -0500, Brad Sanborne wrote:

Even if we take a 36mm width as a standard 35mm-film frame for a virtual
equivalent negative-size for both, then the P&S image is being viewed with
a 29x magnifier and the dSLR image is being viewed with a 36x magnifier
when viewed at 1:1 on a 96-dpi monitor.

Yep, wrong as it comes.

-Wolfgang