Re: immersion objectives with NA <1.0 - useable dry?

From: Dr. Georg N.Nyman (gnnyman_at_swissonline.ch)
Date: 01/31/05 

Date: Mon, 31 Jan 2005 09:56:27 -0700

justbeats wrote:
> If an oil immersion lens has an iris that allows the N.A. to be reduced
> below 1.0 - can it be used without oil?
>
> Similarly - if an immersion lens without an iris is rated with an N.A.
> of (say) 0.9 or less - then can it too be used dry?
>
> I'm finding oil to be a messy deterrent to using high powers.
>
> Incidentally - who supplies xylol in the UK? Or is there a "safe"
> substitute these days?
>
> Thanks
> Beats
>
You should not use these lenses without immersion liquid as these lenses
  base their imaging performance on a medium between front lens and
specimen cover glass. If you use them dry, you get an image but it is
very very hazy and not at all good. Besides this you loose the
correction quality as well. Replacing the immersion oil with something
different is possible but tricky because the refractive indext of the
replacement liquid needs to be as close as possible to the one of the
immersion oil.
Reducing the nA - well possible but you loose resolving power of the
lens and deteriorate the image quality as well. The immersion lenses
have a higher nA to get to a higher resolution as well.
Yes it is messy but there is not really an other way to close the
optical path between the cover glass and the front lens as the
refractive index of air is about 1 and the one of immersion liquids
around 1.5 or sometimes even much higher ( for mineralogical specimen up
to over 1.8 )
rgds George

Relevant Pages

  • Re: Question re Olympus Universal Condenser
    ... indeed any immersion lens, when used without oil. ... You showed us before an Ap image of yours made WITH immersed condenser ...
    (sci.techniques.microscopy)
  • Re: Zeiss Lens nomenclature/relative merit
    ... while others apparently do not require oil. ... Would a lens which does not require oil be more desirable, ... One point to watch out for: the more complex lenses of the 160mm era are generally excellent value on the second hand market, but do watch out for delamination. ... Note that, whatever tube length and class of objectives you use, pairing them with the correct eyepieces is important. ...
    (sci.techniques.microscopy)
  • Re: Is This Microscope a good deal?
    ... I would make SURE that any 100X lens advertised is oil immersion. ... All the scopes I've ever worked with were 100X oil but I know microscope makers can put any number of different lenses on a scope so I don't know what is available in the marketplace. ... Staining at home is an extremely messy proposition unless you have a sink and area around the sink dedicated to being ruined by stains. ...
    (sci.bio.microbiology)
  • Re: 100X oil/non oil affordable objectives
    ... unreachable to microscopy amateurs. ... Do you think that a 100X oil objective at that price can be ... One alternative to oil is water immersion, with NA up to 1.22, about as ... stuff along a range of optical depth, with or w/o cover slip. ...
    (sci.techniques.microscopy)
  • Re: immersion objectives with NA <1.0 - useable dry?
    ... This is because your lens is corrected for an NA of 1.25 or higher. ... Water immersion objectives require water. ...
    (sci.techniques.microscopy)