One thought that occurs to me, (also using a 1024 scan head), is that vibration can cause a problem with any optical system. Normally these appear as lines across the image but could show in other forms. We have never traced the exact source of the problem in our lab but when I floated the optical table the images were  significantly improved. The laser we were using at the time was fibre coupled but I have also used a free space beam into the scan head when small displacements can cause significant variations across the image. 

These problems will vary depending on your position within the building, the time of day, (traffic can cause significant problems in some buildings), and if other equipment is operating, even in other rooms. One way to help to determine if this is the problem is to tap the table top, causing vibrations, and to see if the images are distorted in the way you are experiencing.

All the best

John Girkin

Dr John M Girkin
Institute of Photonics
University of Strathclyde               Tel 44 (0)141 553 4120
Wolfson Centre                  Fax 44 (0)141 552 1575
Glasgow G4 0NW                  e-mail [log in to unmask]
UK



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From:   Dr Pedro J Camello[SMTP:[log in to unmask]]
Sent:   06 May 1999 17:49
To:     [log in to unmask]
Subject:        Bio-Rad photomultiplier

Hi all,
I work (well, I try to) with a laser scanning confocal microscope, a
1024 Bio-rad equipped with two lasers (Ar 100 mW and He-Ne 547) and
two detectors. For 2-3 months the technical service has been unable
to resolve the following problem: I was "reading" DHDCFA-labelled
cells when I realised the signal displayed suspicious  changes. When
I used a slide with fluorescent beads I also got an ugly noise. Is
not a fast and broad noise but slow deviations from the theoretical
mean which should be the "center" of the noise. These changes in the
baseline are sometimes related to other electrical equipment,
sometimes not (I also got this noise using the electric supply of
a patch-clamper, the best of my Faculty), and they go up and down
without any apparent reason. Only a part can be attributed to
temperature changes in my opinion. Bio-Rad engineers blame the
electric supply, but the problem was also present using an isolated
line. Has anybody in the list experienced this kind of problems with
Bio-Rad or any other made? Any suggestions (apart from
cursing Bio-Rad)?

Dr Pedro J Camello
Dpt Physiology
Fac Veterinary Sciences
Univ of Extremadura
PO Box 643
10071 Caceres
SPAIN