Re: Optical artefact removal: reply

Posted by Aryeh Weiss on Jul 19, 2006; 8:13am
URL: http://imagej.273.s1.nabble.com/Optical-artefact-removal-reply-tp3702090p3702095.html

Jacqui Ross wrote:

>
> The artifact is seen with all objectives and I have cleaned them myself to
> make sure it is not due to any film on the lens. It is not visible down the
> eyepieces but only apparent on the images from the camera.
>
>
>
> As Joel also commented, the size of the artifact is consistent through all
> objectives and is visible at different focal planes.
>
>
>

You should check whether the ring pattern changes (or disappears) when you
change the condenser diaphragm. If the condenser diaphragm is too small, then
you are providing partially coherent illumination, and this allows a speck of
dust in a non-image plane along the light path to produce that kind of pattern.
If you increase the NA of the condenser, this may remove the artifact, but then
be sure to cut down the camera gain (exposure) to avoid saturation.

A corollary of this is that the entire light path may need to be cleaned, but
the dust generally returns as fast as you can clean it off.

--aryeh
--
Aryeh Weiss
School of Engineering
Bar Ilan University
Ramat Gan 52900 Israel

Ph:  972-3-5317638
FAX: [phone]