Re: Condenser lens choice for a given objective

Posted by Michael Model on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Condenser-lens-choice-for-a-given-objective-tp7584901p7584934.html

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As I understand, the effect of condenser on theoretical resolution comes
from the fact that its opening makes illumination less coherent and closing
makes it more coherent. There is no simple formula for that. There was a
paper that from the 1950s where this was explained and calculated,
 Unfortunately I don't have the reference with me

Mike

On Mon, Mar 21, 2016 at 11:47 AM, Stanislav Vitha <[hidden email]> wrote:

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>
> My understanding is that in brightfield mode with axial light (condenser NA
> = 0), resolution d=lambda/NA
>
> With strictly oblique illumination where the angle of illumination equals
> the
> acceptance angle of the objective (0th order light travels through one edge
> of the lens, while the 1st order light travels through the opposite edge),
> the
> resolution is doubled: d=0.5*lambda/NA.
>
> With Kohler illumination, i.e. illuminating with a solid cone of light at a
> variety of angles, where the condenser NA = objective NA, the resolution is
> somewhere in between:
> 0.5*lambda /NA < d < lambda/NA
> So for this setup, the Rayleigh formula (0.61*lambda/NA) is actually closer
> to reality than the Abbe formula (0.5*lambda/NA), in my opinion.
>
> For a standard brightfield setup, lateral resolution depends on the total
> NA
> of the system, i.e. the average of the objective NA and the condenser NA,
> where the effective condenser NA is equal or less than the objective NA.
>
> This is what Guy was indicating in his earlier post, I think.
>
> Since the effective NA of illumination is only as large as the NA of the
> objective, increasing the condenser NA beyond the NA of the objective
> (e.g.,  using a 20x/0.5 objective, condenser aperture opened to NA=0.9) is
> not going to increase resolution.
>
> Source:
> R. Wayne: Light and Video Microscopy. Academic Press, New York, 2009.
> ISBN 978-0-12-374234-6
>
>
>
> Stan Vitha
> Texas A&M University
> Microscopy and Imaging Center
>
>