On Fri, 15 Apr 1994, Ulrich Seydel wrote:
 
> A request for help...
> We are using a MRC-1000 confocal microscope. This instrument displays a
> signal of pixel intensity 7, even after the dark current has been
> completely subtracted by the offset (black level). Changes of the offset
> (black level) will not alter this signal
> and thus we have to use this pixel
> intensity as the zero point of the instrument. Has anybody an idea where
> this signal comes from and how to correct it? Thank you very much in
> advance.
 
The adjustments of the black level control the dc output of the PMT. The
pixel intensity you see is the "interpretation", if you like, of this
voltage level by the A/D converter on the scan card.
I suspect that the A/D converter needs to be calibrated (usually by
turning a small screw at the edge of the board) to show 0 for 0 input.
 
 
Stamatis Pagakis
University of Oxford, Dept. of Zoology
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