Just to be devil's advocate:  are you sure you're not adjusting the black
level so that the differences are magnified to 50 grey levels?

Maybe something is wrong with the shape of the pinhole(s)?

> ----------
> From:         Aryeh Weiss[SMTP:[log in to unmask]]
> Reply To:     Confocal Microscopy List
> Sent:         Thursday, July 15, 1999 1:22 PM
> To:   [log in to unmask]
> Subject:      Field uniformity on an MRC-1024
>
> I found that when imaging a uniform fluorescent block, the resulting image
> is
> not uniform (even well beyond the acceptance criterion). Even after
> allignment
> of the
> mirrors, there can be a variation of as much as 50 grey level across the
> field
> at zoom=1.
>
> What is worse -- the variation across PMT3 do not track the variations
> across
> PMT1 and PMT2. The variation across PMT1 and PMT2 track reasonably
> closely, but
> not perfectly.
> This means that it is not just nonuniform illumination.
> It also means that comparing relative strengths between channels is
> difficult,
> and in the case of PMT3, probably not possible at zoom=1.
>
> For higher zooms, the results are of course better, but even at zoom=2
> PMT3 is
> not great.
>
> Is there any experience out there -- particularly among MRC-1024 users --
> that
> may
> be useful for me on this problem?
>
> Thanks in advance
> --aryeh
> --
> Aryeh Weiss                          | email: [log in to unmask]
> Department of Electronics            | URL:
> http://optics.jct.ac.il/~aryeh
> Jerusalem College of Technology      | phone: 972-2-6751146
> POB 16031                            | FAX:   972-2-6751275
> Jerusalem, Israel                    | ham radio: 4X1PB/KA1PB
>