I have a question with regard to Dr. M Cannell's post of
Mon, 29 Jan 1996, Dr M Cannell wrote:
 
> Dear Ralph
> We have used a water immersion lens from Zeiss. It works perfectly
> well in the inverted mode (surface tension keeps the water there). I
> must disagree with the comment by Dr. Kamair (see below) that oil
> immersion lenses are preferable. The water immersion lens has three
> benefits: 1) a reduction in spherical aberration which 2) allows you
> to focus deeper into thick aqeous specimens. 3) This lens will remove
> the  axial foreshortening of the image due to the refractive index
> mismatch. As a note, you should use this lens with the correct
> thickness coverslip, without the coverslip you will not achieve
> diffraction limited performance so focussing into deep petri dishes
> without a coverslip is not the correct way to use this lens.
>
Is the last statement true in the inverted mode? Since the coverslip (now
on top between the illumination and the specimen) is not in the image
path, is the refractive index important. And relatedly, since the petri
dish or slide does not match the refractive index of the lens, is not the
image degraded?
 
Thanks-
 
Jay Jerome
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