Re: Digital Reflex on microscope

From: Tom Knight (tk_at_csail.mit.edu)
Date: 07/02/04 

Date: 01 Jul 2004 20:30:25 -0400

Richard J Kinch <nobody@nowhere.com> writes:
> The only point of interest for me here was my original statement that more
> resolution (defined in the digital-camera-advertising sense, as total
> quantity of resolved pixels, not spatial resolution, perhaps another
> confusion?) requires bigger lenses, aside from improvements in sensor
> technology. If that contradicts "basic principles", then go ahead and hold
> me and my ignorance in contempt.

One source of confusion here is the issue of what is done when more
pixels are added to the sensor. If the pixel size is held constant,
then a physically larger lens is needed to illuminate the larger sensor
with the same light per unit area. That lens will have (likely) the
same F-number as the smaller lens required for a smaller sensor.

But another possibility for increasing resolution is to shrink the
pixel size, maintaining the *same* sensor area. The identical lens
will now provide the identical illumination *per unit area* to the
sensor. But *each pixel* will receive less light.

As the pixels get smaller, they need less light, just as a smaller
area of film needs less light. The reason for this is that the
capacitance of the pixel is going down at the same time as the amount
of light is going down, and the two factors cancel one another. Now,
each of the pixels will exhibit greater noise, due to quantization of
photons captured, but this is not the same thing as having the
exposure incorrect.

Most cameras use very high density, small sensors. Very expensive
35mm SLR compatible systems use sensors the same size as a 35mm film,
but these are out of the range of amateurs. When camera makers
increase the pixel count, it is almost always done by making the
pixels smaller, and keeping the sensor area approximately the same.
This raises the noise level, but such is life.

Relevant Pages

  • Re: Low cost image sensor
    ... >I have been searching the web for a low cost image sensor. ... read to 0.1mm resolution which actually means a minimum of 200 pixels ... realistically 400 pixels would be better to ensure the resolution. ... Ideally I would like no moving parts, and no lens. ...
    (comp.arch.embedded)
  • Re: Low cost image sensor
    ... >>I have been searching the web for a low cost image sensor. ... > read to 0.1mm resolution which actually means a minimum of 200 pixels ... > realistically 400 pixels would be better to ensure the resolution. ... Ideally I would like no moving parts, and no lens. ...
    (comp.arch.embedded)
  • Re: More pixels are better, much of the time
    ... so a sensor the size of the 20D with pixels the size of the F828 ... But what you did is shoot the 828 tests with the 828 lens, ... not a medium telephoto (WA lenses are difficult to design due to ...
    (rec.photo.digital)
  • Re: Why full-frame?
    ... >>The other has to do with the actual size of the pixels, ... > larger pixels on a bigger sensor which can hold more of them, and a lens ... > to compete with MF film? ... >>sensor size is the image circle of the lenses in question, ...
    (rec.photo.equipment.35mm)
  • Re: Resolution question
    ... That really is an insane number of pixels per mm. ... (The limit on lens performance is diffraction. ... sensor, giving you larger pixels. ... People with more sense than money who own cameras like the 1Dsmk2 or 5D will ...
    (rec.photo.digital)