Re: [ATM] Re: [atm_free] The zonal Foucault test is free ofinherentcorrection bias - some supporting graphs

[Ken Hunter <atm_ken_hunter@yahoo.com>]

A simple MicroScope cover glass is close enough to a
Pellicle for ATM use. Works fine.

Ken Hunter


--- Guy Brandenburg <gfbrandenburg@yahoo.com> wrote:
> The book by Strong does recommend use of a pellicle
> made of lacquer on glass, removed by water. I didn't
> know what a pellicle was, so I just looked it up and
> found this at 
> 
>
http://optical-components.globalspec.com/LearnMore/Optics_Optical_Components/Optical_Components/Pellicle_Beamsplitters
> 
> "About Pellicle Beamsplitters
> 
> "Pellicle beamsplitters are constructed from thin,
> nitrocellulose films that are stretched and cemented
> to rigid supporting rings. Pellicles are very
> delicate
> and liable to resonate to certain vibration
> frequencies.  Unlike thicker beamsplitters, pellicle
> beamsplitters have the major advantage of
> eliminating
> second surface reflections by making them coincident
> with the original beam. 
> 
> "Pellicle beamsplitters are available either coated
> or
> uncoated.  Uncoated pellicles yield an average
> reflectivity of 8% from 375–2400 nm. Uncoated
> pellicles reflect 10% of the incident light when
> used
> at 45 degrees, thus providing a useful,
> low-intensity
> side beam, thus they are often used in beam sampling
> applications. Coated pellicle beamsplitters provide
> equal reflectance and transmission over the same
> range.  Coated pellicles are generally manufactured
> with two different coatings, dielectric and
> Inconel®. 
> Dielectric coatings are designed for a specific
> wavelength.  Inconel coating contains nickel,
> chromium, cobalt, and iron. A thin Inconel film
> balances the transmission of each element, resulting
> in a wavelength neutral coating.
> 
> "Pellicle beamsplitters have several advantages over
> plate beamsplitters.  Unlike plates, the thinness of
> pellicle beamsplitters causes very little ghosting. 
> Additionally, they foster a very low incidence of
> chromatic and spherical aberrations.  Finally, they
> cause only negligible alterations in the optical
> path.
> 
> 
> "However, pellicle beamsplitters are very fragile
> devices and are sensitive to environmental factors. 
> They are easily damaged, and should never be
> touched. 
> When cleaned, pellicles should never be wiped or
> bushed.  They should simply be allowed to dry in
> clean, moving air.  Their drum-like design (film
> stretched over a frame) makes them susceptible to
> acoustic interference.  Care should be taken to
> minimize this type of disturbance while they are in
> use.
> ...
> "Related keywords: pellicle beamsplitter, pellicle
> beam splitter, beamsplitter pellicle"
> 
> --- "Richard F.L.R. Snashall" <rflrs@rcn.com> wrote:
> > Guy Brandenburg wrote:
> > 
> > > I am currently browsing a newly-acquired copy of
> > John
> > > Strong's book on laboratory physical techniques
> > > (formerly out of print but available from
> Lindsay
> > > Books as a reprint). He points out that Foucault
> > tests
> > > are sensitive to parallax, and has a method of
> > working
> > > around that by using a half-silvered mirror so
> > that
> > > the examiner's eye and the ray of light coming
> out
> > > towards the mirror are in exactly the same spot.
> > > I know that I always have about an inch or two
> of
> > > parallax when I use a Couder mask.
> > >
> > > Guy
> > 
> > I had always heard that one of the difficulties
> here
> > was the aberration
> > introduced in the transmission through.  That was
> > reduced by using
> > a pellicle (sp?).
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
> > 
> 
> Guy  Brandenburg
> Washington, DC
> My home page:
>
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


		
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