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<!-- comment -->
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Microscope objectives: Immersion</title>
<link rel="stylesheet" href="stylesheets/style.css">
<link rel="stylesheet" href="stylesheets/prism.css">
<script src="javascript/python-highlighting/prism.js"></script>
<script async src="javascript/Minimal-MathJax/MathJax.js?config=TeX-AMS_CHTML"></script>
<script src="javascript/update_figures.js"></script>
<script src="javascript/reference_list/reference_list.js"></script>
</head>
<body>
<section>
<a href="https://amsikking.github.io/">Home page</a>
<h1>amsikking: Microscope objectives</h1>
<a href="./index.html">Index</a>
<h2>Immersion</h2>
<p>
The space between the front of an objective and the image plane
is an important part of the system, where the shape and
refractive index matter. So objectives are designed to account
for this space, and 'expect' an <em>immersion</em> medium of
known refractive index \(n_i\) (and sometimes a coverslip of
very particular specification). Filling the space with a
substantially different refractive index (or coverslip) causes
spherical aberration and produces blurry images at high
numerical aperture
(<a class="citation" href="https://doi.org/10.1007/978-0-387-45524-2"
title="Handbook of Biological Confocal Microscopy, third edition;
J. Pawley; p157 , Springer US, ISBN 978-0-387-25921-5,
eBook ISBN 978-0-387-45524-2, (2006)">Pawley 2006</a>).
</p>
<p>
When imaging a sample of refractive index \(n_s\) beyond the
depth 'zero' image plane (i.e. focusing into the sample at some
finite depth), slabs of immersion (with the correct refractive
index) are effectively exchanged for slabs of sample.
If the sample and immersion are <em>refractive index matched</em>
then this is a 'null' operation and the objective will image as
designed. However, if the sample and immersion refractive index
are substantially different, then the images get blurrier with
depth. So, in general, we require the condition:
\[n_i = n_s \tag{1}\]
</p>
<figure>
<img src="figures/immersion.png" alt="immersion.png">
<figcaption>
(<a href="figures/objective_sketches.odp">.odp sketch</a>)
</figcaption>
</figure>
</section>
</body>
</html>