"Smith reflector"

[Hobbyst46]

Hello all,
In an article from the year 2000, "The use of interference reflection contrast in the examination of diatom valves " by Siver and Hinsch,

I found that epi-illumination through a "Smith reflector" on a Leica microscope enhanced the resolution of diatoms. It seems that the only component required for IRC is that reflector.

I began searching for the "Smith reflector" and found that it is an accessory of (modern) Leica upright microscope. But did not find details about its construction and how exactly it works. Or is it a proprietary Leica accessory ?
Thanks in advance for shedding light (pun) on the reflector.

[PeteM]

I'm curious as well. It appears to be a "cube" that is used in both upright and inverted Leica microscopes able to accept epi cubes (brightfield, darkfield, fluorescence, etc.) - with applications similar to a brightfield cube but somehow improving resolution. Perhaps by eliminating stray light??

Page 25 and 26 of this inverted Leica DM manual have a brief description and photo of the cube. It contains a 22.5 deg. beam spliter, a 22.5 degree mirror, and a compensating lens. The cube also shows up in the Leica DM L upright manuals:

https://content-calpoly-edu.s3.amazonaw ... Manual.pdf

[MichaelG.]

This may be of interest : http://www.minsocam.org/msa/openaccess_ ... ptr_01.pdf

Optical path is illustrated.

The Smith reflector (Figure lAb) involves light entering so as to fall on a mirror at an angle of22.5°, from which it is reflected at the same angle onto a glass plate. This plate functions in the same way as the coated 45° plane-glass reflector, although its efficiency as a reflector is slightly less. However, the incident beam of polarized light is subject to less rotation (see Chapter 4), and an isotropic sample between crossed polars appears uniformly dark.

MichaelG.

.

Ref. http://www.minsocam.org/msa/openaccess_ ... g_vaughan/

[PeteM]

Thanks, Michael. I wonder if the improvement in epi DIC resolution is all that much from what sounds like a slight improvement in control of the polarization?

On the other hand, member Scarodactyl has noted problems with Olympus epi DIC showing a faint double image in some cases. Maybe the fault lies in the polarizers?

[MichaelG.]

Excellent point, Pete

I am not familiar with the device, but I suspect that the improvement in resolution may be attributable to the higher contrast of a ‘Smith’ image.

MichaelG.

.

Although it’s from a different discipline …
Figure1 in this paper nicely illustrates the effect of contrast upon apparent resolution:
https://www.researchgate.net/publicatio ... ts_science

[Scarodactyl]

From glancing at the article I don't know that the smith reflector was even the deciding factor--they seemed to be comparing it to transmitted DIC. From skimming it was unclear to me whether they specified what type of DIC they were using (in terms of high contrast or high resolution--maybe Leica doesn't do that the way Nikon or Olympus do.) I dunno, maybe I should actually read it.

[MichaelG.]

.

Eureka !!

Francis Hughes Smith is our hero

Director of Optical Design, C. Baker Instruments Ltd., Croydon.

and 377782 his US patent

MichaelG.

.

Dr. Smith’s interesting obituary can be found here :
https://archive.org/stream/NewsUK1993UK ... 9_djvu.txt

[MichaelG.]

From glancing at the article I don't know that the smith reflector was even the deciding factor--they seemed to be comparing it to transmitted DIC. From skimming it was unclear to me whether they specified what type of DIC they were using (in terms of high contrast or high resolution--maybe Leica doesn't do that the way Nikon or Olympus do.) I dunno, maybe I should actually read it.

^^^ Agreed

The closing statement reads

Configuring a light microscope that has epi-illumination capabilities for IRC optics is simple and inexpensive, and allows the user to instantly switch between standard transmission and IRC optics. In addition to enhancing our ability to resolve the structure of diatoms, we have also noted significantly improved resolution of siliceous scales from synurophytes. We challenge investigators working on other types of algae to examine their specimens using this technique.

I think the Smith reflector was probably just part of the the standard IRC configuration for that microscope

See __ MATERIALS AND METHODS | Configuration of the microscope.

MichaelG.

.

IRC : https://en.wikipedia.org/wiki/Interfere ... microscopy

[Hobbyst46]

Thanks PeteM, MichaelG, Scarodactyl,

Some reading material !

The subject of IRC makes me curious. It appears that, first of all, the diatom must be in very very close proximity to the coverslip. Within microns or less.
Second, interference reflection differs from DIC.
A polarizer is an option in the IRC setup (not a must) - the idea is that reflected light is polarized (to some extent).

Incidentally, having the diatoms really touch the coverslip means that the chance of success of the IRC with prepared and arranged diatom slides is low - since for preparation, a layer of adhesive must separate the diatoms from the glass. If that layer is reasonably "thick", to hold the diatom strongly, then...

Another point: the authors mounted their diatoms either in Hyrax or in air. I did not see that they compared between air-mounted and resin-mounted.
And they used only the 100/1.3 immersion objective. So the thin layer of air between the diatom and coverslip had no negative effect !?

P.S. the same technique had been used to study fibroblasts on glass...