Re: How many pixels?

On Thu, 20 Apr 2006 02:26:31 GMT, "NoSpam" <NoSpam@xxxxxxxxxxx> wrote:




What about final magnification at the camera sensor? I.e., if the
oculars are 10X and the objective is 100X, the final mag is 1,000X.
This assumes that the camera is parfocal with the oculars (which can
be done).



Gary Gaugler, Ph.D.
Microtechnics, Inc.
Granite Bay, CA 95746
916.791.8191
gary@microtechnics dot com

Final magnification of the image in the exit pupil, whether it is by an
eyepiece
for the observer's eye of by a lens projecting the image upon the CCD array
can not increase the number of elements into which the microscope objective
has resolved the object.

The lens relaying the image formed in the exit pupil merely serves to
match the size of the resolution elements formed in that pupil to the
properties
of the detector. In the case of the human eye, the image must be enlarged
enough
so that each element subtends the angle of resolution of the eye. In the
case of a
CCD array each resolved element (pixel) in the exit pupil must be adjusted
to
the physical size of a pixel in that array.

If excessive magnification is used, then for the case of the eye, the image
will
just be larger but will not contain additional detail. This is referred to
as empty
magnification. If too little magnification is used then the image seen by
the
eye will miss some of the information contained in the exit pupil.

Similarly excessive magnification for a CCD will lead to one resolution
element
illuminating two or more array pixels in the camera. No additional inform-
mation is gained, while array pixels are used up. If not enough
magnification
is used two or more resolution elements will illuminate one CCD pixel and
information will be lost.

There are of course other considerations in imaging, such as the number of
shades
of grey or of color which are rendered by the final medium, the strength of
the signal
compared to noise and others. While they may affect the extent to which the
elements
resolved at the level of the exit pupil of the objective may be discerned in
the final
product, be it vision or image, they can't improve upon the performance of
the
objective.

I am reasonably sure that this explanation is correct, but I would
appreciate
further comments.

G.R.



So a 10X factor at the CCD makes no difference?


Gary Gaugler, Ph.D.
Microtechnics, Inc.
Granite Bay, CA 95746
916.791.8191
gary@microtechnics dot com
.

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