Posted by
Lutz Schaefer on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Southeastern-Microscopy-Society-meeting-tp4640594p4643246.html
Michael,
spherical aberration (SA) is mostly caused by refractive index mismatches
between immersion and embedding. Also, using cover slips and immersion media
that are different from the manufacturers recommendations will cause more or
less SA. Often we model the system between front element and sample with 3
parallel layers of RI. Optimally, the manufacturer has corrected the
objective with aberrations of the opposite sign, so your induced SA cancels
out. Still, for example whenever the embedding has different RI than the
immersion, the best way to have the least amount of SA is to stay close to
the cover slip with your sample. Now, if you have no ICS optics (older
microscopes) you may have a chance to do some SA compensation by changing
that tube length, which will also slightly change the working distance. The
same is true for changing other parameters in the 3 layer system. In an ICS
you can only do the latter. Although SA depends linear on some of the model
parameters, you cant really say that the wave front generally diverges or
converges in presence of SA, because that could rather somewhat better
explain defocus. Because it is hard to describe in a few simple words how a
wave front behaves, one usually uses diffraction theory (e.g. "Principles of
optics", Born & Wolf). This is a very well understood, rigorous theory,
enabling to quantify complex amplitudes and their polarization, or if you
wish just intensities. I would understand, when not all aspects of
diffraction theory are detailed in a book that focuses on general
microscopy, but then I am not sure what books you were referring to.
Regards
Lutz
____________________________________
Lutz Schaefer
Advanced Imaging Methodology Consultation
16-715 Doon Village Rd.
Kitchener, Ontario, N2P 2A2
Phone/Fax: (519) 894 8870
Email:
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Website:
http://home.golden.net/~lschafer/____________________________________
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From: "MODEL, MICHAEL" <
[hidden email]>
Sent: Friday, February 26, 2010 3:54 PM
To: <
[hidden email]>
Subject: tube lens and spherical aberration
> (I apologize if this is a second post, I got some strange errors from the
> first one)
>
> Dear List
>
> It's not a confocal question, it's strictly a wide-field question... When
> people talk about spherical aberration they typically start with a
> parallel beam falling on an objective, and then, for whatever reason, the
> objective fails to bring all the rays into a common focus. In wide-field,
> one has a luminous spot in the object space, and the effect of spherical
> aberration would be a failure of the objective to collect all the rays
> into a single parallel beam. Some rays will form a converging (or
> diverging) cone instead. Then, this cone will be received (I suspect that
> in the case of a diverging cone, some light may even get lost on its way)
> by a tube lens and form a blurry spot on the image plane. My question is,
> Is this situation really equivalent to the standard one considered in all
> books? (I suspect, it's not because even the distance to the tube lens
> should make a difference). But I would be very interested in the opinion
> of those who understand optics better than I do. Thanks!
>
> Mike Model
>
> Michael Model, Ph.D.
> Confocal Microscopy,
> Dpt Biological Sciences,
> 1275 University Esplanade,
> Kent State University, Kent, OH 44242
> tel. 330-672-2874