Thank you very much for your response! 
I scanned slides with 4um beads and the stretching seems to be at least 20% 
of the bead. It is hard to say precisely because of blurring. 
I checked beads mounted with vectasshield, water and immersion oil. The 
biggest extension was in the water, and there was almost no extension in oil 
(the spheres looked almost round in xz and yz). I know that it is not anything 
new, but I think that it confirms that refraction index is in huge part 
responsible for this aberration if not alone.

Best regards,

Michal Gdula


Subject: Re: Correction of Z-axis distortion- request for opinion 
From: Guy Cox <[log in to unmask]> 
Reply-To: Confocal Microscopy List 
<[log in to unmask]> 
Date: Sat, 4 Apr 2009 03:10:11 +1100 
Content-Type: text/plain 

Well, the stretching should be 1.518 / 1.457 if simple RI difference is the 
cause - ie about 4%.  If you are seeing more than that you'd better look 
elsewhere - maybe a dodgy Z drive?  I suppose changes in SA with depth 
would add to the discrepancy, but that depends a lot on how great a depth 
you are measuring through.  Also, though it's true oil and coverslip should 
have the same RI, oil changes with temperature whereas glass doesn't (much) 
so if you  can use #1.5 and still have enough working distance it might be 
better.   

                                       Guy