Posted by
Joel Sheffield on
Jul 18, 2006; 7:06pm
URL: http://imagej.273.s1.nabble.com/Optical-artefact-removal-tp3702076p3702084.html
It is not at all clear where the artifact comes from. We have had
the same effect with infinity corrected lenses. The size of the
rings is independent of the objective magnification. It is unaffected
by microscope focus.
I like Joachim's suggestions about the structure of the camera. It
could easily be an internal reflection problem of some sort. It does
not appear to be a function of the camera focal length --at least
within the zoom ranges that are used for microphotography.
If the sample is complex, and fills the field, i.e. a tissue section,
the effect of the artifact is minimal. However, if there is an
extensive area of background, or if the illumination is dim, the
artifact becomes prominent.
Interestingly, it is sufficiently consistent that it can be removed
by background subtraction procedures that use a "no sample" image, as
long as intensity is kept constant.
Joel
> Hi all,
>
> >It is right that this is a specific coolpix artefact, it is present
> >for models after CP-995 (4500, 5000) It is due to the photosites size
> >(usually for digital cameras the improvements for general
> >photography are bad things for microscope microphotography).
>
> Hmm, are you referring to some kind of moire effect? However, I could
> not understand how this should show up on a presumed homogeneous
> (resp. non-periodic) background!?
>
> As I understand they are using non-infinity objectives in some kind of
> infinity position, I would assume (the order of this effect depends
> greatly on the focal length of the objctive used) that they need to
> defocus so much that a normally unnoticed (becaused totally out of
> focus) internal reflex becomes near focus and noticeable, maybe this
> is even a bad coincidence with the reflection from the "cover glass"
> (or whatever, I don´t know the layout of coolpix cameras) in front of
> the chip, so it might disappear with other cameras, because they have
> that glass in another position!
>
> Joachim
>
>
>
>
>
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Joel B. Sheffield, Ph.D.
Biology Department, Temple University
1900 North 12th Street
Philadelphia, PA 19122
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