Re: Optical artefact removal

Posted by Stanislav Vitha on Jul 19, 2006; 5:03pm
URL: http://imagej.273.s1.nabble.com/Optical-artefact-removal-tp3702076p3702078.html

Dear Jacqui,
I have used the Coolpix 995 and Coolpix4500 on different compound
microscopes and was able to suppress the ring artefact to reasonable
levels. The severity of the artefact may vary from camera to camera,
but it is apparently caused by the spin-cast manufacturing process of
Coolpix lenses:
http://www.couger.com/microscope/shootout/shootout.html

I found that the ring artefact is less obvious if I zoom out with the
Coolpix as much as possible. People sometimes make the mistake of
zooming in all the way to maximum to gain (useless) magnification -
the rings are then pretty visible. So zoom in only enough to remove
the vignetting - it depends on your adapter (eyepiece) how much zoom
is necessary - the closer is the eyepiece to the front of the coolpix
lens, the better - in my adapter the lenses were only about 1 mm
apart, so not much zoom was needed. Some of the genuine Nikon
adapters had the front element recessed too much and a lot of zoom
was needed to remove vignetting.

Of course, if you need reproducible magnification, it would be nice
to set the zoom to the same numerical value each time the camera is
used. There is some free software that can be used for this purpose
and also can be used as a remote shutter. I can provide more detail off-list.

On my Olympus BH2 microscope the artefact was also less severe with
lower magnification objectives than with the oil 100x/1.3.

Regards,
Stan

At 01:40 AM 7/18/2006, you wrote:

>Dear All,
>
>
>
>I have had an enquiry from someone from another Department who has an
>artefact affecting their imaging which looks like a diffraction effect
>(e.g. Newton rings) when doing transmitted light microscopy.
>
>
>
>I had a look at their microscope and camera system and even when Koehler
>illumination is set up properly, you still get this effect. The
>microscope is a rather old Nikon inverted microscope with a Coolpix
>attached. The objectives, (phase contrast), are not infinity corrected
>and I'm assuming that there is also a problem with the tube length for
>the camera. The rings are there irrespective whether specimens are on
>glass or in plastic dishes. I don't think much can be done optically
>(correct me if I'm wrong) but I wondered if some image processing could
>help.
>
>
>
>My ImageJ question is this:
>
>
>
>Is it possible to use some kind of image processing (e.g. image
>subtraction) to remove this artifact? I have tried a few things out
>(e.g. Image calculator, rolling ball) without much success so far.
>
>
>
>I have posted 2 images at the following address:
>http://www.health.auckland.ac.nz/biru/exptal_images/index.html There are
>also links to larger images although the original images are even larger
>than these.
>
>
>
>Please note that I do know that these images are appalling! I asked one
>of the students to send me one image with tissue (glass slide) and one
>without at the same focal plane and this is what I got! I don't think
>they set up the microscope very well. However, you can see the rings
>clearly on both images so I hope they will inspire someone to suggest a
>solution.
>
>
>
>I would be very pleased to hear of any potential solutions.
>
>
>
>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/
><http://www.health.auckland.ac.nz/biru/>
>
>

Dr. Stanislav Vitha      [hidden email]
Microscopy and Imaging Center
Texas A&M University
BSBW 119
College Station, TX 77843-2257

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