Re: Optical artefact removal: reply

Posted by Jacqueline Ross on Jul 19, 2006; 11:31pm
URL: http://imagej.273.s1.nabble.com/Optical-artefact-removal-reply-tp3702090p3702091.html

Hi Aryeh,

Thanks for your comments. The field diaphragm and condenser aperture are
set up for Koehler so as to match the NA of the objective lens. The
consistency of the pattern and its central location do seem to indicate
a systemic fault.

Cheers,

Jacqui.

Jacqueline Ross
Biomedical Imaging Research Unit
School of Medical Sciences
Faculty of Medical & Health Sciences
The University of Auckland
Private Bag 92019
Auckland, NEW ZEALAND

Tel: [phone] Ext 87438
Fax: [phone]

http://www.health.auckland.ac.nz/biru/ 
-----Original Message-----
From: ImageJ Interest Group [mailto:[hidden email]] On Behalf Of
Aryeh Weiss
Sent: 19 July 2006 19:13
To: [hidden email]
Subject: Re: Optical artefact removal: reply

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]