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It is normal but irritating.

The lasers cannot be completely switched off - the LSM700 is a budget  
confocal.
However although you can see the laser light its level is very low -  
but with a bright specimen and pushing the detection limits it can be  
produce a detectabe image - scanning with the lasers nominally off.

There is therefore a risk of bleaching part of the specimen in a  
timeseries. A solution is to use the multiposition acquisition and  
sacrifice one position.
However we have not noticed a photobleaching problem - but it is easy to test.





Quoting "Z.J. Zhang" <[log in to unmask]>:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Hi everyone:
>
> I am having a weird problem with my Zeiss LSM 700 confocal  
> microscope and hope you could shed light on it -
>
> When I tried to scan with the lasers off (turning the lasers off via  
> the ZEN software), I can literally see a relatively bright light  
> coming from the objective! The light looks white, which I assume is  
> the combination of the blue, green and red lasers. Although the  
> detected fluorescence signal is 'minimal', it still worries that 1).  
> It might photobleach my sample; and 2). When I scan with one laser,  
> the other lasers might be on as well, so I wouldn't know what  
> exactly I am scanning with!
>
> I was told by Zeiss that this is "normal" because there are no  
> mechanical shutters in the scan head. I have a hard time to believe  
> it and here are my questions:
>
> 1). Does anyone experience the same/similar problem?
> 2). What could be the possible cause?
> 3). How am I supposed to fix it?
>
> Thank you,
>
> Zhaojie
>
> Zhaojie Zhang, Ph. D.
> Director, Jenkins Microscopy Facility
> University of Wyoming
> Laramie, WY 82071
> PHONE: 307-766-3038
> FAX: 307-766-5625
>



Jeremy Adler
IGP
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