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I'm not really familiar with the details of the
Zeiss but if it's zooming both images to the same
screen size it's not surprising that 444x444 looks
awful.  One also needs to bear in mind that if pixels
are above ~0.2mm in a display they will become visible.

The Nyquist criterion is 2.3 pixels per minimum resolved
distance (not 2 as some have suggested).  It can often be
worth going to 3 to have some margin of error - especially
since this allows one to use a median filter to reduce noise
without using resolution.

There are also times - such as when plotting the profile of
a bead image to get FWHM - when sampling well above Nyquist
are justified, but this isn't regular imaging.

These topics are covered in Chapter 6 – The digital image in
my book Optical Imaging Techniques in Cell Biology (shameless
plug but if Jim can do it why can't I).

                                                     Guy


> Search the CONFOCAL archive at
> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
>
> I have been following this thread and I understand the Nyquist theorem
> and why it has to be followed.
>
> We have a Zeiss LSM 510 and when you apply digital zoom and then click
> on the "Optimal" button it sets the frame size so that the pixel
> dimensions meet the Nyquist sampling rate (approximately).  So if you're
> using the 40x water objective with a zoom factor of 1 it tells you the
> optimal frame size is 2048 x 2048 but when you zoom to 4x and click
> optimal it sets the frame size to 444 x 444, which keeps the pixel size
> at about .12um (approximately Nyquist based on the resolution of the
> scope).  That makes sense to me, but what I don't get is why at 4x zoom
> my picture looks a whole lot better if I set the frame size to 2048 x
> 2048.  At this point each pixel is 0.027um, which is way beyond the
> resolving power of the scope and Nyquist, but it's a much better looking
> image if I go to 2048.
> Can anyone explain this to me?
>
> Thanks,
> Ben Troutwine
>


-- 
Associate Professor Guy Cox
Electron Microscope Unit,
University of Sydney,
NSW 2006, Australia

Phone:+61 2 9351 3176    Fax:+61 2 9351 7682
http://www.guycox.net