limit of accuracy by pixelpitch

[nj]

is it correct that the pixelpitch determines the smallest feature detected on an image?

given an image scale of 1:200 and a desired accuracy of 1mm, this millimeter will be 5micron on the sensor. if the pixelpitch of the camera is larger than 5 micron would the claim to accuracy of 1mm still be given ?

what defines the limit of accuracy concerning resolution? … if all conditions and specs of optics, light geometry and texture would be just ideal?

[bigben]

If you can't resolve it on the sensor, you can't resolve it in the image

[nj]

If you can't resolve it on the sensor, you can't resolve it in the image

sure, for a single spot, but what happens at an edge (perfect geometrical intersection of two surfaces) ?
the exact geometric information of that edge would get lost but the intersection of this surfaces ( different shades ) would still be there and visible on the pictures … given the stated example of 1mm accuracy … one couldn't fulfill this demand of accuracy?!

[photogrammetrix]

Hi all,
 <pixel-pitch> is commonly defined as the direct distance of the photosensitive detector elements on your imaging sensor. It is one of the factors that influences the performance of your imaging system but there are a lot more. I also was wondering about all the facts influncingt he process of imaging with digital sensors some time ago and digged a bit into it. Other important aspects are:

- numerical aperture
- aperture  /  f-stop
- ratio of wavelenth  / diameter of aperture
- light diffraction / Airy disks
- Rayileigh criterion
- Modular transfer function (MTF), image contrast, object contrast
- signal to noise ratio of your sensor
- distortion characteristics of your lens
- etc, etc, etc,

here is one "rule of thumb" to get a number for distance of the objects to ge them resolved with an optical system


for common cameras, separation distance of
objects can be approximated:
                         f                           f        1
x = 1.22 * L * ­­­ ---          with      --- ­­­ = ----    ­­­ =  f-­number
                         D                         D      2NA
x = distance between two objects
L = wavelength       f = focal length     
D = apertur diameter  NA = numerical aperture

Some conclusion from all that stuff to consider:

diffraction sets fundamental resolution
limit independent of number of megapixels

depends only on the f­number of lens, and
on the wavelength of light being imaged

it reduces small­scale contrast by
causing airy disks to partially overlap

tiny pixel sizes of high megapixel point­
and ­shot cameras can only be exploitet
with high­ quality lenses and f­number < 2

Or in other words: the sensor in your camera body is one thing to consider but there is another one in frontt of it - the lens with it' aperture, which is not of minor importance . Without a good lens  the best sensor will only yield average image quality.

There is a saying amongst photographers: "Invest in glass!" :-)

Cheers and have fun