>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
 
 
You put your slide with the coverslip DOWNWARD on
an inverted scope.  It's a good idea to make sure
it is sealed on ....
                                Guy Cox